Viruses and Prions Lecture Notes PDF

Viruses and Prions Viruses Obligate intracellular parasites: Require living host cells to multiply Have few to no enzymes for metabolism No ATP-generating mechanism Definitive features: Contain DNA or RNA; not both Contain a protein coat that protects the nucleic acid...

Viruses and Prions Viruses Obligate intracellular parasites: Require living host cells to multiply Have few to no enzymes for metabolism No ATP-generating mechanism Definitive features: Contain DNA or RNA; not both Contain a protein coat that protects the nucleic acid Multiply inside living cells using host cell machinery Hinders antiviral drug development Produce structures to transfer viral nucleic acid to other cells Viruses Host range: the spectrum of host 65 nm cells a virus can infect Capsid (head) Host range varies depending on the DN A virus (very specific to broad) Shea Many viruses infect only specific th types of cells in one species of host Tail organism fiber Determined by specific host attachment Pi sites and cellular factors n Basepl ate For example, bacteriophages are Bacteriop hage viruses that only infect bacteria Viruses Range from 20 nm to 1000 nm in length Bacteriophage 800 × 10 nm M13 970 Bacteriophages f2, 24 nm MS2 nm Ebola Poliovir 30 virus us nm Rhinovir 30 us nm Adenovir 90 Chlamydia 300 us nm bacterium E. coli nm Rabies 170 × 70 bacterium elementary body virus nm 3000 × 1000 Prio 200 × 20 nm n nm Human red blood Bacteriophage 225 cell T4 nm 10,000 nm in diameter Tobacco mosaic 250 × 18 Plasma virus nm membrane Viroi 300 × 10 of red blood d nm cell 10 nm thick Vaccinia 300 × 200 × virus 100 nm Viruses Virion: complete, fully developed viral particle, capable of causing infection Virion Structure All virions possess Nucleic acid—DNA or RNA can be single- or double- stranded; linear or circular Capsid—protein coat made of capsomeres (subunits) Together, these two structures compose the nucleocapsid Viruses Virion Structure All virions possess Spikes—projections on outer surface used for entry into the host cell Some virions also possess Envelope—lipid, protein, and carbohydrate coating on some viruses Taken from the host membrane when virus exits Virus Multiplication – Animal Viruses 1. Adsorption: virus attaches to receptors on host cell membrane 2. Penetration and Uncoating: virus enters cell in a vacuole by membrane fusion (enveloped viruses) or receptor- mediated endocytosis (naked viruses). Enzymes in vacuole dissolve membrane and capsid to release DNA 3. Synthesis: nucleic acid replication and protein production 4. Assembly: nucleic acid and capsid proteins come together to form nucleocapsid 5. Release: by budding (enveloped viruses) or rupture (naked viruses) Virus Multiplication – Animal Viruses 1. Adsorption: virus attaches to receptors on host cell membrane 2. Penetration and Uncoating: virus enters cell in a vacuole by membrane fusion (enveloped viruses) or receptor-mediated endocytosis (naked viruses). Enzymes in vacuole dissolve membrane and capsid to release DNA Entr y Host plasma membrane Fusion of viral proteins at site of receptor- envelope and plasma mediated endocytosis membrane Virus Multiplication – Animal Viruses 3. Synthesis: nucleic acid replication and protein production DNA viruses DNA replication – nucleus Protein synthesis – cytoplasm RNA viruses RNA replication and protein synthesis – cytoplasm  Virus Multiplication – Animal Viruses 4. Assembly: nucleic acid and capsid proteins come together to form nucleocapsid 5. Release: by budding (enveloped viruses) or rupture (naked viruses) Viral capsid Budding – virus acquires portion of host cell Host cell plasma membrane membrane; cell may live Viral Rupture – Nonenveloped viruses escape protein through holes in membrane; host cell Bu typically dies d Bu d Release by budding Envelo pe Pathogenic Properties of Viruses Evade host defenses by growing inside host cells Immune cells can not reach them Cytopathic Effects of Viruses (CPE) Visible effects of infection Often cytocidal: result in cell death May be used to diagnose infection Vary with virus Key difference is point in infection when they occur Pathogenic Properties of Viruses Cytopathic Effects of Viruses (CPE) Stopping cell synthesis Causing cell lysosomes to release enzymes Creating inclusion bodies in the cell cytoplasm Typically contain aggregated proteins and may represent sites of virus replication Very diagnostic; can help identify causative agent Fusing cells to create a syncytium Cytoplasmic mass Inclusion (syncytium) body Nuc lei Pathogenic Properties of Viruses Pathogenic Properties of Viruses CPE and Cancer Changing host cell function or inducing chromosomal changes Activating oncogenes Loss of contact inhibition in the cell, leading to cancer Viruses and Cancer Integration of oncogenic viruses can activate oncogenes Oncogenes Involved in cell growth and proliferation or inhibition of apoptosis Dozens have been identified Activated oncogenes allow cells designated for apoptosis to survive and proliferate Normal cells transform into tumor cells Acquire properties of cancer Altered growth from normal cells Cells may express tumor-specific antigens on the cell surface and in the nucleus Viruses and Cancer Oncogenic viruses (oncoviruses) can become integrated into the host cell’s DNA and induce tumors ~10% of cancers are virus-induced Oncoviruses often go undetected until cancer formation because: Most virions do not induce cancer Cancers may develop long after initial infection Cancers caused by viruses are not contagious  Persistent Viral Infections Latent infection: periods with no infectious virus; reactivation may occur due to changes in immunity Chronic infection: infectious virus present at all times; occurs gradually over a long period Chro nic Chroni c Chro nic Virus Multiplication in Bacteriophage Lytic cycle (lysis) Phage causes lysis and death of the host cell Lysogenic cycle (latency) Phage DNA is incorporated into the host DNA Virus Bacter Bacterial Caps DN Multiplication in ial chromoso id A cell me Capsid wall (head) Shea Adsorption: Bacteriophage th Tail Phage attaches fiber Basepl Tai l to host cell. ate Pi n Cell wall Plasma Penetration: membrane Phage penetrates host cell and Lytic cycle injects its DNA. Sheath Synthesis: Results in cell death contracted Phage DNA Tail by lysis directs synthesis core of viral (disintegration of cell components Tai DN by disruption of cell (DNA, proteins, l A wall or membrane) etc.) by the host Assembly: Viral cell. components are assembled into Caps virions. id Release: Host cell lyses, and new virions are released. Tail fibers Virus Multiplication in Bacteriophage Lysogeny: phage remains latent (dormant or inactive) Phage DNA incorporates into host cell DNA Called a prophage When the host cell replicates, prophage is replicated Lysogenic phages can reproduce using both the lytic and lysogenic cycles  Virus Multiplication in Bacteriophage The Lysogenic Cycle: phage remains latent (dormant or inactive) Phage DNA incorporates into host cell DNA Phage attaches to host cell and Occasionally, the prophage may excise from the bacterial chromosome Phage DNA Called a prophage (double-stranded) injects DNA. by another recombination event, initiating a lytic cycle. Prophage is replicated Bacterial chromosome when the host cell replicates Many cell divisions Lytic Lysogenic cycle cycle Cell lyses, releasing Phage DNA circularizes and enters Lysogenic bacterium phage virions. lytic cycle or lysogenic cycle. reproduces normally. Prophage OR New phage DNA and Phage DNA integrates within the proteins are synthesized bacterial chromosome by recombination, and assembled into virions. becoming a prophage. © 2016 Pearson Education, Inc. Virus Multiplication Propha gal ge gene Prophage exists in galactose-using host – Bacteriophage Galactose- (containing the gal Positive gene). donor cell gal gene Phage genome excises, carrying with it the Outcomes of lysogeny adjacent gal gene from the host. Immunity to infection by gal Phage matures and same phage gene cell lyses, releasing phage carrying gal gene. Specialized transduction Galactose- negative Phage infects a cell recipient cell that cannot Specific bacterial genes utilize galactose (lacking gal transferred to other bacteria gene). by phage Along with the Changes genetic properties prophage, the bacterial gal gene of the bacteria becomes integrated into the new host's DNA. Lysogenic cell can now metabolize galactose. Galactose- positive recombinant Virus Growth Viruses must be grown in living cells Bacteriophages are grown in bacteria Phages form plaques, which are clearings on a lawn of bacteria on the surface of agar Each plaque corresponds to a single virus; can be expressed as plaque- forming units (PFU) Plaques Virus Growth Growing animal viruses In living animals In embryonated eggs Virus injected into egg growth signaled by changes or death of embryo In cell cultures Tissues are treated with enzymes to separate cells Virally infected cells are detected via their deterioration, known as the cytopathic effect (CPE)  PrPSc Prions PrPSc Proteinaceous infectious particles PrPc produced by PrPSc may be cells acquired or is secreted to the produced by an cell altered PrPc gene. Cause of nine animal neurological surface. diseases Spongiform encephalopathies – large vacuoles develop in the brain PrPSc reacts with PrPSc converts the PrPc PrPc on the cell to PrPSc. surface. Inherited and transmissible by ingestion, transplant, and surgical instruments The new PrPSc The new PrPSc is converts taken Cause of cell damage not yet known more PrPc. in, possibly by receptor- Lysoso mediated me PrPC: normal cellular prion protein, on the endocytosis. cell surface PrPSc: scrapie protein; accumulates in brain Endoso cells, forming plaques PrPSc accumulates me PrPSc continues to in accumulate endosomes. Some as the endosome may contents are be transferred back returned to the cell to the cell surface. surface or are transferred to Microbial Nutrition and Growth Microbial Nutrition Essential nutrient: required chemicals that microbes cannot make on their own; must be provided to the organism Macronutrients: required in relatively large quantities and play principal roles in cell structure and metabolism i.e. carbon, hydrogen, and oxygen Micronutrients: present in much smaller amounts; involved in enzyme function and maintenance of protein structure Also known as trace elements i.e. manganese, zinc, nickel Microbial Nutrition Chemical Analysis of the Microbial Cytoplasm Water — 70% of cytoplasm Proteins Organic compounds — 97% of dry cell weight Elements (C, H, N, O, P, S) — 96% of dry cell weight Most chemical elements are available to the cell as compounds, not as pure elements Only a few types of nutrients needed to synthesize over 5,000 different compounds Microbial Nutrition Elements % Dry Weight Chemical Composition of E. coli Carbon (C) 50 Oxygen (O) 20 Organic % Dry Weight Nitrogen (N) 14 Compounds Hydrogen (H) 8 Proteins 50 Phosphorus (P) 3 Nucleic Acids– 20 RNA Sulfur (S) 1 Nucleic Acids– 3 Potassium (K) 1 DNA Sodium (Na) 1 Carbohydrates 10 Calcium (Ca) 0.5 Lipids 10 Magnesium 0.5 Miscellaneous (Mg) Inorganic % Dry4Weight Compounds Chlorine (Cl) 0.5 Water (none in dry Iron (Fe) 0.2 weight) Trace metals 0.3 All others 3 Microbial Nutrition How organisms obtain carbon Heterotroph: must obtain carbon from organic sources i.e. glucose metabolism Autotroph: uses inorganic CO2 as its carbon source Can convert CO2 into organic compounds Not nutritionally dependent on other living things How organisms obtain energy Chemotroph: obtains energy from chemical compounds Phototroph: uses photosynthesis Microbial Nutrition Category Energy Source Carbo Example n Sourc e Autotroph Photoautotroph Sunlight CO2 Photosynthetic organisms, such as algae, plants, cyanobacteria Chemoautotroph: Organic compounds CO2 Methanogens Chemoorganic autotrophs Chemoautotroph: Inorganic CO2 Thiobacillus, “rock-eating” Chemolithoautotrop compounds bacteria (minerals) hs Heterotro Photoheterotroph Sunlight Organi Purple and green ph c photosynthetic bacteria Chemoheterotroph Metabolic Organi Protozoa, fungi, many conversion of the c bacteria, animals nutrients from other organisms Chemoheterotroph: Metabolizing the Organi Fungi, bacteria Saprobe organic matter of c (decomposers) Microbial Nutrition Heterotrophs and Their Energy Sources Chemoheterotrophs derive carbon and energy from organic compounds Process these molecules through cellular respiration or fermentation Saprobes Decomposers of plant litter, animal matter, and dead microbes Recycle organic nutrients Parasites Derive nutrients from the cells or tissues of a living host Many are pathogens cause damage to tissues or even death; cause disease Microbial Nutrition – Transport Mechanisms Transport of necessary nutrients occurs across the cytoplasmic membrane, even in organisms with cell walls The driving force of transport is atomic and molecular movement Diffusion: the phenomenon of molecular movement, in which atoms or molecules move in a gradient from an area of higher density or concentration to an area of lower density or concentration  Microbial Nutrition – Transport Mechanisms Osmosis: the diffusion of water through a selectively permeable membrane: Membrane pores allow free diffusion of water, but block certain other dissolved molecules (solutes) Water moves in relation to the solute concentration The osmotic relationship between cells and the environment is determined by the solute concentration on either side of the plasma membrane Microbial Nutrition – Transport Mechanisms Osmosis Isotonic solutions: solute concentrations equal inside and outside of cell; water is at equilibrium Solut Plasma Cytopla e membrane sm Cel Isotonic l solution wa No net ll movement of Wat water occurs er Microbial Nutrition – Transport Mechanisms Osmosis Hypertonic solutions contain a higher concentration of solutes (i.e. NaCl) than inside the cell Causes plasmolysis (cell cytoplasm shrinks) due to high osmotic pressure Foods preservation (i.e. salted fish and honey) Plasma Plasma membr Cell membr H2 ane wall ane Cell in O Cell isotonic Cytopl plasmolysis Cytopl solution asm in hypertonic asm solution NaCl NaCl 0.85% 10% Microbial Nutrition – Transport Mechanisms Osmosis Hypotonic solutions: solute concentration is lower outside than inside the cell; water moves into cell Rigid cell wall prevents osmotic lysis in bacteria Plasma membrane rupture due to excess water moving into cell Hypotonic solution Water moves into the cell Strong cell walls contain the swelling Weak or damaged cell walls burst (osmotic lysis) Microbial Nutrition – Transport Mechanisms Microbial Nutrition – Transport Mechanisms Movement of materials across membranes Passive processes substances move from high concentration to low concentration no energy used Active processes Nutrients transported against or with the natural diffusion gradient, but faster than diffusion alone Use specific membrane proteins (permeases and pumps) Require energy These processes occur in both prokaryotes and eukaryotes Microbial Nutrition – Transport Mechanisms Movement of materials across membranes – Passive processes Outsid e Simple diffusion: molecules move from an area of high concentration to an area of low concentration Plasma Continues until molecules reach equilibrium membra ne Insid e Simple diffusion through the lipid bilayer  Microbial Nutrition – Transport Mechanisms Movement of materials across Transpo membranes – Passive processes Nonspe rted Specific cific substan transpo Facilitated diffusion: transport transpo ce rter proteins move molecules from areas rter of high concentration to areas of low concentration Gluc ose Facilitated diffusion Facilitated diffusion through a through a specific nonspecific transporter transporter  Microbial Nutrition – Transport Mechanisms Movement of materials across membranes – Passive processes Aquapo rin Osmosis: movement of water across membrane from an area of high water concentration to an area of lower water concentration Through lipid layer or Aquaporins (water channels) Osmosis through the lipid bilayer (left) and an aquaporin (right) Microbial Nutrition – Transport Mechanisms Movement of materials across membranes – Active processes Carrier-mediated active transport Atoms or molecules pumped into or out of cell by specialized receptors. Requires energy Microbial Nutrition – Transport Mechanisms Movement of materials across membranes – Active processes Endocytosis Cell encloses the substance in its membrane Simultaneously forms a vacuole and engulfs the substance Phagocytosis Accomplished by amoebas and white blood cells Ingest whole cells or large solid matter Pinocytosis Ingestion of liquids such as oils or molecules in solution Environmental Factors that Influence Microbes Most research relevant and medically relevant microbes can only live when specific physical and chemical conditions are met Physical factors Temperature pH Osmotic pressure Chemical factors Oxygen (required element for nutrition) Environmental Factors that Influence Microbes Extremophiles – microbes that thrive in physical or chemical conditions that typically kill most microbes Dhakar, K., Pandey, A. Wide pH range tolerance in extremophiles: towards understanding an important phenomenon for future biotechnology. Appl Microbiol Biotechnol 100, 2499–2510 (2016). https://doi.org/10.1007/s00253-016-7285-2  Environmental Factors that Influence Microbes - Temperature Microbes grow well within a limited temperature range Growth temperatures Minimum – lowest temperature that supports growth Optimum – best temperature for fastest growth Maximum – highest temperature that supports growth Min and max growth temps Typically ~30oC/86oF apart Poor growth at these temps http://www.uwyo.edu/virtual_edge/images/  Environmental Factors that Influence Microbes - Temperature Three primary groups based on preferred temperature range Mesophiles – moderate-temperature-loving (25-40oC/77- 104oF) Psychrophiles Most common type – cold- of microbe loving (-20-15oC/4- 59oF) Polar regions or deep in ocean Thermophiles – heat- loving (50-60oC/122-  Environmental Factors that Influence Microbes - Temperature Two additional classifications Psychrotolerant (Psychrotrophs) – Optimal temp @ 20-30oC/68-86oF, but can grow @ 0oC/32oF and spoil food Extreme thermophiles (hyperthermophiles) – very high temps (≥80oC/176oF)  Environmental Factors that Influence Microbes - pH Most bacteria grow near neutral pH Acids produced during bacterial fermentation inhibit growth Food preservation (i.e. sauerkraut, cheese) Molds and yeasts grow between pH 5 and 6 https://sciencenotes.org/the-ph-scale-of-comm Environmental Factors that Influence Microbes – Osmotic Pressure Environmental Factors that Influence Microbes - Oxygen Microbes that use molecular oxygen (O2) obtain more energy from nutrients than those that do not However, O2 is very toxic depending on its form O2 radicals “steal” electrons from other molecules, converting them to dangerous forms and disrupting essential cellular processes. Superoxide radicals: O2− Peroxide anion: O22− Phagocytic white blood cells use radical forms of O 2 to destroy pathogens Environmental Factors that Influence Microbes - Oxygen Bacteria that grow in the presence of O2 produce superoxide dismutase (SOD) Enzyme that converts superoxide radicals (O2−) into molecular oxygen (O2) and hydrogen peroxide (H2O2) Environmental Factors that Influence Microbes - Oxygen The peroxide anion (O22-) of hydrogen peroxide is also toxic Principle for use in wound treatment Converted by catalase or peroxidase Catalase Peroxidase reaction reaction Environmental Factors that Influence Microbes - Oxygen Obligate aerobes — require oxygen Facultative anaerobes — grow via fermentation when oxygen is not available Anaerobes — unable to use oxygen and most are harmed by it Aerotolerant anaerobes — tolerate but cannot use oxygen Microaerophiles — require oxygen concentration lower than air  Environmental Factors that Influence Microbes - Oxygen Microbes can be classified based on their ability to use O2 and how O2 affects their growth The Study of Bacterial Growth – Binary Fission Bacterial growth = increase in cell Cell Plasma wall membrane number, not cell size Cell elongates Bacteria typically reproduce and DNA is replicated. DNA through binary fission (nucleoid ) Parent cell splits into two new cells Cell wall and plasma membrane begin to Cell constrict. wall Partially Cross-wall formed forms, cross-wall completely separating DNA the (nucleoid) two DNA copies. Cells Plasma separ membra ate. ne Bacterial Division and Generation Time Binary fission doubles the cell number every generation Total number of cells = 2number of generations Generation time - time required for a cell to divide Ranges from 20min to 24hr  Bacterial Division and Generation Time Exponential growth results in enormous increases in bacterial cell numbers between later generations For example, E. coli doubles every 20min 21 generations (7hr) – Over 1 million cells 30 generations (10hr) – 1 billion cells 72 generations (24hr) – 1021 cells Growth curves are represented logarithmically Arithmetic graphs are not meaningful Bacterial Division and Generation Time (Log10 = 6.02) Plot type Logarith (Log10 = mic Arithmet 4.52) ic (524,2 (Log10 = 88) 3.01) (Log10 = 1.51) (262,1 44) (131,0 72) (65,5 36) (32,7 (3 (102 2) 4) 68) Bacterial Phases of Growth Bacterial growth curves Display growth on logarithmic scale over time Four main phases Both the stationary and death phases may be due to factors such as the accumulation of waste, depletion of available nutrients, pH changes, etc. Direct Measurement of Bacterial Growth Bacterial populations are typically very large Methods rely on counting small samples of the larger population Calculations are then used to determine cell number in original sample Direct measurements – counting microbial cells 1. Plate count 2. Filtration 3. Most probable number (MPN) method 4. Direct microscopic count Direct Measurement of Bacterial Growth Plate Counts Plate bacteria and count the resulting colonies or colony-forming units (CFUs) Count plates with 30 to 300 colonies (CFUs) US FDA recommends 25-250 colonies/plate Serial dilutions of original sample provide plates with colonies in this range https://fankhauserblog.files.wordpress.com/1988/06/  Direct Measurement of Bacterial Growth Plate Counts Serial dilution of samples provide plates with 30-300 colonies for accurate measurement  Direct 1.0 or 0.1 Measurement of Inoculat e empty 0.1 ml ml Inoculate plate containin Bacterial Growth plate. g solid Bacte medium. rial Plate Counts diluti on Spread inoculum Counts are performed on Add over surface melted bacteria mixed into a dish nutrient evenly. agar. with agar (pour plate method) or spread on the surface of a plate (spread Swirl to mix. plate method) Colonies grow Colonies only on grow on surface and of in medium. solidifie d medium. Microbial Metabolism Chapter 7 Metabolism and the Role of Enzymes Metabolism: cellular chemical reactions that buildup and breakdown nutrients Provides energy and creates substances that sustain life Anabolism: the synthesis of cell molecules and structures; uses energy Catabolism: Breaks the bonds of larger molecules into smaller molecules; releases energy Metabolism and the Role of Enzymes Simplified model of metabolism Metabolism and the Role of Enzymes Bacterial metabolism can have positive and negative effects Positive – Nitrogen cycle, food production, sewage treatment Negative – Disease and food spoilage The ability of bacteria to grow and thrive in certain environments is directly related to their metabolism Differences in metabolism between bacterial species are based on differences in the enzymes expressed by bacteria Type and amount of expressed enzymes is based in the bacterial genome How do Enzymes Work Enzymes are biological catalysts Catalysts: Increase the rate of chemical reactions Do not become part of the products Are not consumed in the process Do not create a reaction Enzymes Have unique active sites that match and bind specific substrates Play a direct role in changing the substrate to products Can function over and over again https://www.scientificamerican.com/article/exploring-enzy  How do Enzymes Work Enzymes drastically speed up chemical reactions by lowering the activation energy Enzyme Structure Simple enzymes consist of protein alone Conjugated enzymes contain protein and nonprotein molecules Holoenzyme: a combination of a protein and one or more cofactors Apoenzyme: protein portion of a holoenzyme Cofactors: organic molecules (coenzymes) or inorganic elements (metal ions) Enzyme-Substrate Interactions Temporary enzyme-substrate union must occur at active site Fit is specific; “lock-and-key” Designated reaction occurs on the substrate may require a cofactor Product is formed and released Enzymes is unchanged and can repeat process Cofactors: Supporting the Work of Enzymes Trace elements are often cofactors for enzymes Iron, copper, magnesium, manganese, zinc, etc. Participate in precise functions between the enzyme and substrate Coenzymes are a type of cofactor Organic compounds; work with apoenzyme Remove chemical groups from one substrate and add to another substrate i.e. hydrogen atoms, electrons, carbon dioxide, and amino groups Many derived from vitamins Regulation of Enzyme Action Enzyme activity is influenced by cell’s environment Natural temperature, pH, osmotic pressure Changes in the normal conditions cause enzymes to be unstable Denaturation Breaking of weak bonds that maintain native shape of apoenzyme Causes distortion of enzyme’s shape and prevents substrate from attaching to active site Regulation of Enzyme Action Constitutive enzymes Always present in relatively constant amounts no matter how much substrate is present i.e. glucose metabolism enzymes Regulation of Enzyme Action Regulated enzymes Turned on (induced) or turned off (repressed) based on amount of substrate available Enzyme induction: Enzymes are made (induced) only when substrate is present Enables organism to use a variety of nutrients Prevents wasted energy on enzymes that aren’t needed (when no substrate is present) Direct Controls on the Action of Enzymes Competitive inhibition Uses a molecule that resembles the enzyme’s normal substrate “Mimic” occupies active site, preventing binding of actual substrate  Direct Controls on the Action of Enzymes Noncompetitive inhibition Some enzymes have two binding sites Active site Regulatory site Molecules bind to regulatory site Slows down enzymatic activity when a certain concentration of product is reached Controls on Enzyme Synthesis Enzyme repression Stops transcription and translation of new enzymes from DNA Metabolic Pathways Usually multistep pathways, with each step catalyzed by an enzyme Products of one step are often reactants in the next step Do not stand alone; interconnected and merge at many sites May have branches for alternate methods of nutrient processing Others have a cyclic form; starting molecule is regenerated to initiate another cycle  Metabolic Pathways Series of enzymatically catalyzed chemical reactions Oxidation – electrons removed Reduction – electrons gained Oxidation and reduction reactions are always coupled Electron Transport Chain (System) Energy Production Adenosine triphosphate (ATP) “Energy carrier” of living cells Possesses unstable bonds that can easily be formed/broken to store/provide energy for the cell Energy Production Microbes can catabolize carbs, lipids, and proteins Most microorganisms use carbs as their primary energy source Carbohydrate Catabolism Breakdown of carb molecules to produce energy Glucose is the most common energy source Glycolysis Oxidation of glucose to pyruvic acid Energy Production After glycolysis, energy production continues by cellular respiration or fermentation  Energy Production Cellular respiration Krebs cycle Oxidation of acetyl CoA produces NADH, FADH2, and 2 molecules of ATP, and liberates CO2 as waste Electron transport chain (system) Series of carrier molecules are oxidized and reduced as electrons are passed down the chain Energy released is used to produce ATP in process called chemiosmosis Energy Production Chemiosmotic generation of ATP  Energy Production Overview of aerobic cellular respiration Energy Production Anaerobic cellular respiration The final electron acceptor in the electron transport chain is not O 2 Anaerobic respiration using nitrate and sulfate as final electron acceptors is essential for nitrogen and sulfur cycles in nature Yields less energy than aerobic respiration Electron Products Acceptor NO3- NO2- , N2 + H2O SO42- H2S + H2O CO32- CH4 + H2O Energy Production After glycolysis, energy production continues by cellular respiration or fermentation Energy Production Fermentation Does not require oxygen Produces ATP quickly Produces 1-2 molecules of ATP Microbes can ferment various substances End products are useful for identification Biochemical Tests Biochemical tests identify bacteria by detecting enzymes Fermentation test: bacteria that catabolize carbohydrates or protein produce acid, causing a pH indicator to change color Can also be used with a Durham tube to detect gas production during fermentation Oxidase test: identifies bacteria that have cytochrome c oxidase Energy Production Energy Production Energy Production Energy Production Lipid and Protein Catabolism Lipids are degraded by extracellular lipases into fatty acids and glycerol Proteins are degraded by extracellular proteases and peptidases into amino acids Metabolic Pathways of Energy Use Most energy given off as heat ~45% of energy from glucose Energy in ATP Transport across plasma membranes – Active transport Movement – flagella Most used in production of new compounds Metabolic Pathways of Energy Use Polysaccharide s Lipids Metabolic Pathways of Energy Use Amino Acids Nucleotides Integration of Metabolism Amphibolic pathways function in both anabolism and catabolism Many pathways function simultaneously with common intermediates Direct Measurement of Bacterial Growth Filtration Solution passed through a filter that collects bacteria Filter is transferred to a Petri dish and grows as colonies on the surface  Direct Measurement of Bacterial Growth Grid with 25 large squares Cover Direct microscopic count glass Volume of a bacterial Sli suspension placed on a de slide Average number of bacteria per viewing field is calculated Bacterial suspension is added here and fills the shallow volume over the squares Bacteria l Microscopic suspens count. ion Cover glass Sli de Location of Perform calculations to squares determine cells per mL Cross section of a cell counter. Indirect Measurement of Bacterial Growth Light source Spectrophot Lig ometer ht Turbidity— measurement of Bla Light-sensitive cloudiness with a Scattered light nk detector that does spectrophotometer not reach detector Bacterial suspension Microbial Genetics and Genetic Engineering Introduction to Genetics and Genes Genetics – the study of inheritance (heredity) of living things; it is wide-ranging and explores: The transmission of biological traits from parent to offspring How those traits are expressed in an organism The structure and function of the genetic material How this material changes The Nature of Genetic Material Genome – the sum total of genetic material of an organism Most of the genome exists as chromosomes Some may be plasmids Cell genomes – DNA Virus genomes – either DNA or RNA The Nature of Genetic Material Chromosome – a distinct cellular structure composed of a neatly packaged DNA molecule Eukaryotic chromosomes: DNA wound around histone proteins Located in the nucleus Diploid (in pairs) or haploid (single) Linear and double-stranded The Nature of Genetic Material Chromosome – a distinct cellular structure composed of a neatly packaged DNA molecule Bacterial chromosomes: DNA condensed into a packet by histone-like proteins One, two, or sometimes several chromosomes DNA is circular and double-stranded The Nature of Genetic Material Chromosomes contain DNA which carries hereditary information within genes Genes – provide information for certain cell functions; encode for protein and RNA molecules Three categories of genes: Structural genes that code for proteins Genes that code for RNA machinery used in protein production Regulatory genes that control gene expression The Nature of Genetic Material Genotype: the sum of all gene types; an organism’s distinctive genetic makeup Phenotype: the expression of the genotype creates traits (structures or functions) https://stamper-geneticshelp.weebly.com/uploads/ The DNA Code Nucleotide – basic unit of DNA structure Phosphate, deoxyribose, and nitrogenous base Nucleotides covalently bond to each other creating a sugar-phosphate backbone Sugars attach in a repetitive pattern to two phosphates One of the bonds is to the number 5′ (“five prime”) carbon on deoxyribose, and other to 3′ carbon The DNA Code Bases between strands interact Purines (A/G) bind pyrimidines (T/C) Adenine (A) always pairs with thymine (T) Guanine (G) always pairs with cytosine (C) Bases interact using weak hydrogen bonds Molecules are easily unzipped to gain access to the information encoded by bases The DNA Code Antiparallel arrangement: one strand runs in opposite direction of other One side runs 5′ to 3′, the other side runs 3′ to 5′ Important factor in DNA synthesis and protein production DNA Replication Enzymes separate existing DNA strands and copy them to create two daughter molecules Daughter molecules are identical to parent in composition Process is semiconservative Each daughter molecule has one new strand and one parent strand Transcription and Translation Transcription: production of RNA from a DNA template Translation: transcribed RNA used to produce protein Exceptions: Some viruses convert RNA → RNA or RNA → DNA A wide variety of RNAs are used to regulate gene function Transcription and Translation Steps in Transcription  Transcription and Translation RNA has structural differences vs DNA Single-stranded, helical molecule Can form secondary and tertiary structures Makes specialized forms (tRNA and rRNA) Contains uracil (U) instead of thymine A pairs with U; G pairs with C Contains ribose rather than deoxyribose The Differences Between DNA and RNA Explained With Diagrams. Owlcation. SHERRY HAYNES (UPDATED: DEC 12, 2023 6:03 PM EST)  Transcription and Translation Many RNA varieties Translational RNAs – ribosomal RNA, transfer RNA, messenger RNA Function in translation (protein production) Regulatory RNAs – micro RNA, anti-sense RNA, riboswitches, small interfering RNA, primer RNA, ribozymes Function in regulating protein production  Transcription and Translation Ribosomes – align mRNA with tRNA during translation Ribosomes in bacteria, mitochondria, and chloroplasts – 70S size Eukaryotic ribosomes – 80S size Small subunit binds mRNA Large subunit supplies enzymes for making peptide bonds  Transcription and Translation Codon: groups of 3 nucleotides Determine which amino acid is added to growing peptide chain 64 triplet codes, but only 20 amino acids Redundancy – Same amino acid represented by several codons Transcription and Translation Redundancy Some amino acids are represented by several codons If mistakes occur (in replication or transcription) the correct amino acid may still be inserted Genetic Regulation of Protein Synthesis Control mechanisms ensure genes are active only when required Enzymes only produced when needed Bacteria, archaea, and eukaryotes use regulatory RNAs (micro RNAs, antisense RNAs, etc.) to control protein production Operons Groups of genes regulated as a single unit Only in bacteria and archaea Genetic Regulation of Protein Synthesis Operons Inducible operons Induced (turned on) by enzyme substrate Often catabolic enzymes (needed when substrate is present) Repressible operons Repressed (turned off) by enzyme product Often anabolic enzymes (stopped when enough product is made) Genetic Regulation of Protein Synthesis Phase variation - bacteria turn on/off genes that lead to obvious phenotypic changes Mediated by regulatory proteins Usually applied to traits affecting surface of bacterial cell Neisseria gonorrhoeae: produce attachment fimbriae Streptococcus pneumoniae: produce a capsule Tan A, Atack JM, Jennings MP, Seib KL. The Capricious Nature of Bacterial Pathogens: Phasevarions and Vaccine Development. Front Immunol. 2016 Dec 12;7:586. doi: 10.3389/fimmu.2016.00586. PMID: DNA Recombination Events Bacteria have no exact equivalent to sexual reproduction Recombination One bacterium donates DNA to another Results in new strain different from DNA donor and recipient Plasmids are adept at interchanging genes Provides genes for antimicrobial resistance, new metabolic capabilities, increased virulence, and adaptation to the environment Recombinant: an organism containing genes originating from another organism Horizontal Gene Transfer in Bacteria Vertical gene transfer: flow of genetic information from one generation to the next Occurs during replication Horizontal gene transfer: transfer of genes between cells of the same generation; new genes did not come from parent organisms Jayashantha, Eranga - Archaea Morphology,  Horizontal Gene Transfer in Bacteria Plasmids: Small, circular pieces of DNA Contain their own origin of replication Replicate independently Not necessary for survival Can carry useful traits Chromosomal fragments: Must integrate into the bacterial chromosome in order to be replicated Plasmids- Definition, Properties, Structure, Types, Functions, Examples. March 13, 2022 by Nidhi Abhay Kulkarni. Edited By: Sagar Aryal. https://microbenotes.com/plasmids/  Horizontal Gene Transfer in Bacteria Conjugation: genetic material transferred from one bacterium to another through direct contact Gram-negative conjugation – genetic material transferred by pilus Fertility (F factor) creates pilus Pilus Gram-positive conjugation – genetic material passes from one cell to another through openings in cell envelope F+ F– cel ce l ll Horizontal Gene Transfer in Bacteria Resistance (R) plasmids Origin Mercur Commonly shared by conjugation of y replicat resista Sulfonam ion nce ide Can transfer genes for: resistanc Streptom e Resistance to multiple antibiotics ycin Pilus resistanc Resistance to heavy metals and e Virulence factors such as toxins, enzymes, conjugat RT Chlorampheni F ion and adhesion molecules proteins col resistance Origin Tetracycl of ine transf resistanc er e R100 plasmid Horizontal Gene Transfer in Recipien t cell Bacteria a b D c A d B C Transformation: Uptake of small DNA fragments from environment (from lysed cells) DNA Chromosoma Aided by DNA-binding proteins on cell wall fragments l DNA Recipient from donor Competent cells can accept genetic material cells cell takes up donor DNA. 53 Requires no special appendages; donor and recipient cells do ' 'a b A D Donor DNA aligns not have to be in direct contact c B C with d complementar y Useful for recombinant DNA technology bases. 5 3 ' ' A D Recombination b occurs c B C d between donor DNA and recipient Degraded DNA. unrecombine d DNA a D B C Genetically transformed cell  Horizontal Gene Transfer in Bacteria Transduction: DNA transfer from donor cell to recipient by a bacteriophage Generalized transduction: Random fragments of disintegrating host DNA are taken up by the bacteriophage During phage assembly, pieces of bacterial DNA may be packaged in a phage capsid. Phage RECOMBINATI protein ON Phage coat Phage DNA DNA Bacteri al A phage carrying Bacterial DNA bacterial DNA infects a chromosome Recipie new host cell. nt Dono A phage infects cell r the Recipie cell donor bacterial Donor nt cell. bacterial bacteri Recombination can occur, DNA al Phage DNA and proteins are producing a recombinant made, Recombinant DNA cell with a genotype and the bacterial cell different from both the chromosome is reproduces donor and recipient cells. broken into pieces. normally Many cell divisions  Horizontal Gene Transfer in Bacteria Specialized transduction: – specific part of host genome transferred by a lysogenic phage Prophage DNA separates from bacterial chromosome, carrying a small segment of host genes with it In lytic cycle, viral and host genes are incorporated into virions and carried to another bacterial cell  Horizontal Gene Transfer in Bacteria Examples of Factors Involved Direct or Genes Commonly Transferred in Mode Indirect* Nature Conjugation Donor cell with pilus Direct Drug resistance; resistance to Fertility plasmid in donor metals; toxin production; Both donor and recipient alive enzymes; adherence molecules Bridge forms between cells to transfer DNA Transformation Free donor DNA (fragment) Indirect Polysaccharide capsule Live; competent recipient cell Transduction Donor is lysed bacterial cell; Defective Indirect Toxins; enzymes for sugar bacteriophage is carrier of donor fermentation; drug resistance DNA; Live recipient cell of same species as donor *Direct means the donor and recipient are in contact during exchange; indirect means they are not.  Horizontal Gene Transfer in Bacteria Transposons (“jumping genes”) Pieces of DNA capable of shifting from one part of genome to another Can move from a chromosome to a plasmid, or vice versa; or from one cell to another Involved in: Trait changes (colony morphology, pigmentation, etc.) Transfer of drug resistance (in bacteria) Infectious Diseases Affecting the Eyes Surface of the Eye and Its Defenses Conjunctiva Thin, membrane-like tissue Covers outer surface of eye (except cornea) and lines the eyelids Secretes oil- and mucus-containing fluid Lubricates and protects eye surface https://www.allaboutvision.com/resources/ Surface of the Eye and Its Defenses Cornea Dome-shaped central portion of eye; located over iris Has 5-6 layers of epithelial cells that regenerate quickly if damaged Called “the windshield of the eye”  Surface of the Eye and Its Defenses Tears are primary defense Consists of aqueous fluid, oil, and mucus Contain lysozyme and lactoferrin Have antimicrobial properties Formed in the lacrimal gland and drain into the lacrimal duct Flow of tears prevents attachment of microorganisms to eye surface  Surface of the Eye and Its Defenses The eye immune response Inflammation does not occur in the eye as readily as it does elsewhere in the body Flooding the eye with light-diffracting objects such as lymphocytes and phagocytes would blur vision Effect of obstructed vision could be worse than effect of microbes or other substances in the eye Immune privilege: vertebrate eye evolution favored reduced immunity Normal Biota of the Eye Previously thought to be only sparsely populated by microbiota 16s rRNA analysis revealed a robust population of diverse bacterial species Corynebacterium is often the dominant genus Eye microbiome resembles skin microbiome Defenses Normal Biota Eye Mucus in conjunctiva and Corynebacterium species s in tears, lysozyme and and other skin colonizers lactoferrin in tears  Conjunctivitis Signs and symptoms Waking with eye(s) “glued” shut by Infection of the conjunctiva secretions that accumulate and Also called red eye or pinkeye solidify overnight Relatively common; numerous causes Bacterial infections – milky Microbes adapted for growth in eye tissues discharge Microbes exposed to eye by contact Viral infections – clear, watery lenses exudate Accidental inoculation by injury Allergic response – clear, watery Allergies fluid is formed Centers for Disease Control and Prevention's Public Conjunctivitis Neonatal eye infections caused by Neisseria gonorrhoeae or Chlamydia trachomatis Transmitted vertically from a genital tract infection in the mother Can lead to serious eye damage if not treated promptly Herpes simplex can also cause neonatal conjunctivitis, but is accompanied by a generalized herpes infection Medical-on-Line/Alamy Conjunctivitis Conjunctivitis in other age groups has numerous causes: Staphylococcus epidermidis, Streptococcus pyogenes, Streptococcus pneumoniae, Haemophilus influenzae N. gonorrhoeae and C. trachomatis – autoinoculation from a genital infection or sexual activity Numerous bacteria, fungi, and protozoa – can contaminate contact lenses and be transferred to eye Viral conjunctivitis – commonly adenoviruses, but others may be responsible Both bacterial and viral conjunctivitis are transmissible by direct contact and are usually highly contagious Keratitis Signs and symptoms: Infection of deeper eye tissues Can lead to complete corneal destruction Causative agents: Miscellaneous bacteria Herpes simplex virus Acanthamoeba Keratitis Herpetic keratitis “Misdirected” reactivation of (oral) herpes simplex virus type 1 (HSV-1) Blindness due to herpes is the leading infectious cause of blindness in the United States Infections with HSV-2 can result from a sexual encounter or transfer of the virus from the genital to the eye area Fluorescein-stained corneal ulcer (green) By Hee K Yang, Young K Han, Won R Wee, Jin H Lee and Ji W Kwon; Department of Ophthalmology, Seoul National  Keratitis Acanthamoeba keratitis Amoeba live in tap water, freshwater lakes, etc. Associated with less-than-rigorous contact lens hygiene or previous trauma to the eye Mild inflammation followed by severe pain May require a corneal transplant ISM/Phototake Infectious Diseases Affecting the Eyes Infectious Diseases Affecting the Nervous System Structure and Function of the Nervous System Two divisions: central and peripheral nervous systems 1. Central nervous system (CNS): brain and spinal cord Control center for body Detects sensory info from environment Interprets info Sends impulses to coordinate body’s activities  Structure and Function of the Nervous System Neurons: cells that make up tissues of brain and spinal cord Receive and transmit signals to and from CNS and PNS Meninges: three layers of continuous membranes Protects the brain and spinal cord  Structure and Function of the Nervous System Cerebrospinal fluid (CSF) Located between layers of meninges Provides Nutrition to CNS Liquid cushion for brain and spinal cord Microbes can be found within the CSF during meningitis Structure and Function of the Nervous System Two divisions: central and peripheral nervous systems 2. Peripheral nervous system (PNS): nerves that branch from CNS The communication lines between CNS, other parts of body, and external environment Consists of nerves and ganglia: Nerves: bundles of axons that receive and transmit nerve signals Ganglion: where cell bodies of neurons aggregate Defenses of the Nervous System Mainly structural: Bony casings of brain and spinal cord protect from traumatic injury CSF provides cushioning Blood-brain barrier Cell layer that prevent solutes in blood from non- selectively crossing into CNS Regulates what can and can not access brain cells Prohibits most microbes and antibiotics from entering the nervous system https://s3.cad.rit.edu/cadgallery_production/images/uploads/faculty-f-projects/ Defenses of the Nervous System CNS is “immunologically privileged”: Partial immune response when exposed to an immunologic challenge CNS functions are vital; temporary damage/inflammation from normal immune responses could be detrimental CSF has low levels of: Circulating antibodies Phagocytic cells Complement (proteins that help immune system destroy microbes) Normal Biota of the Nervous System Believed that there is no normal biota in either the CNS or PNS: Microbes in these tissues indicates disease Of note, latent herpesviruses in the nervous system are not normal microbiota Defenses Normal biota Nervous Bony structures, blood-brain barrier, None System microglial cells, and macrophages Diseases of the Nervous System Meningitis: inflammation of the meninges Encephalitis: inflammation of the brain Meningoencephalitis: inflammation of both Most common routes of CNS invasion are through the bloodstream and lymphatic system Inflammation can alter permeability of blood-brain barrier Meningitis Meningitis: inflammation of the meninges https://www.headway.org.uk/media/6538/diagram-showing-how-meningitis-affects-the-brain-including-the-meninges-around-the-brain-copyright-  Meningitis Caused by a variety of pathogens Bacteria, viruses, fungi, protozoa Viral meningitis is more common but usually mild Symptoms Triad of fever, headache, and stiff neck Followed by nausea and vomiting May progress to convulsions and coma https://pmpediatrics.com/wp-content/uploads/iStock- Meningitis Bacterial meningitis ~50 species cause disease as opportunistic pathogens Typically caused by three species (all 3 possess a capsule) Neisseria meningitides Streptococcus pneumoniae Haemophilus influenzae type b Progression Microbes access bloodstream Travel to and enter CNS Death from shock and inflammation Survival often results in neurological damage  Meningitis – Neisseria meningitidis meningitis Also called meningococcal meningitis Caused by Neisseria meningitidis Gram-negative diplococcus with capsule Microbiota of nose and throat in ~40% of people Begins as a throat infection, rash, and bacteremia Symptoms mostly from endotoxin (outer membrane) Death can occur within hours after fever onset https://medchrome.com/wp-content/uploads/2010/08/ https://www.microbiologyinpictures.com/bacteria N.meningitidis.jpeg %20photos/neisseria%20meningitidis%20photos/ https://microbewiki.kenyon.edu/images/thumb/4/43/Meni_mt002.jpeg/300px-  Meningitis – Neisseria meningitidis meningitis Typically in children under 2yr old Highest incidence in “meningitis belt” in sub- Saharan Africa Mortality of 9–12% with antibiotic therapy; 80% without Vaccination protects against 5 out of 6 strains https://www.cdc.gov/travel-static/yellowbook/2020/map_4-10-small.png Meningitis – Streptococcus pneumoniae meningitis Also called pneumococcal meningitis Caused by Streptococcus pneumoniae Gram-positive, diplococcus with capsule 70% of people are healthy nasopharyngeal carriers Most common in children (1 mo – 4 yr) High mortality: 8% in children, 22% in the elderly Prevented by vaccine https://microbenotes.com/wp-content/uploads/2018/02/Biochemical-Test-of- Meningitis – Haemophilus influenzae meningitis Caused by Haemophilus influenzae type b (Hib) Gram-negative, possesses capsule Normal throat microbiota Occurs mostly in children (6 mo to 4 yr) Prevented by the Hib vaccine Incidence decreasing due to vaccine https://i1.wp.com/medicoapps.org/wp- content/uploads/2018/10/1489312093.jpeg? w=1020&ssl=1 http://www.bacteriainphotos.com/photo%20gallery/Haemophilus Meningitis – Cryptococcus neoformans meningitis Caused by Cryptococcus neoformans Soil fungus found in pigeon and chicken droppings Produces very thick capsule Respiratory transmission through dried, contaminated droppings Affects immunocompromised Spreads through blood to the CNS Mortality up to 30% Treatment with antifungals Meningitis – Listeria monocytogenes meningitis Caused by Listeria monocytogenes Gram-positive rod Excreted in animal feces Wide distribution in soil and water Common food contaminant Psychrophile – foodborne illness https://ars.els-cdn.com/content/image/3-s2.0-B9780123847317000398-f00039-01- Meningitis – Listeria monocytogenes meningitis Initial infection is called listeriosis Usually mild or symptomless Typical foodborne illness symptoms (fever and diarrhea) During an adult infection, bacteria can invade the bloodstream and reach CNS Meningitis more common in the immunocompromised https://www.pnas.org/content/  Neonatal Meningitis – Listeria monocytogenes meningitis If listeriosis occurs in pregnant women, bacteria can cross placenta May lead to stillbirth Disease typically manifests as meningitis weeks after birth Infant mortality rate ~60% https://www.pnas.org/content/  Meningitis – Diagnosis and Treatment CSF samples taken by spinal tap or lumbar puncture Requires prompt and careful handling CSF pathogens do not survive well outside of body Immediate Gram staining, culturing, and other tests Chemotherapy initiated before diagnosis Due to rapid disease progression and threat of mortality Broad-spectrum antibiotics More specific treatment after identification Zika Virus Disease Causative agent: Zika virus Signs and symptoms Adults: none to skin rash, conjunctivitis, and muscle/joint pain Congenital Zika virus syndrome Acquired by fetus during gestation Microcephaly: babies born with abnormally small heads Small head, vision problems, involuntary movements, seizures, and irritability  Zika Virus Disease Transmission and epidemiology Mosquito bite, sex with infected individuals, and vertical transmission 80% of infections are asymptomatic Congenital Zika virus syndrome occurs in 5-10% of infected mothers Prevention and treatment No vaccine currently available Provide supportive measures Poliomyelitis Causative agent: Poliovirus Nonenveloped virus: can survive gastric environment after ingestion Spreads through food, water, hands, objects contaminated with feces Most cases Initial symptoms – sore throat and nausea Virus moves to tonsils and lymph nodes Transient viremia may occur; no clinical disease Poliomyelitis Causative agent: Poliovirus ~1% of cases Viremia persists and virus enters CNS Infects and destroys motor nerve cells Results in paralysis; death from respiratory failure https://images.medindia.net/infographics/article-images/950_400/symptoms-of- Poliomyelitis No cure; can only be prevented Vaccine available Polio cases fell 99% from 1988 to 2000 Persistent reservoirs of polio remain in Pakistan and Afghanistan Meningoencephalitis Meningoencephalitis: inflammation of the brain and meninges Caused by amoebas (protozoa): Naegleria fowleri Acanthamoeba Accidental parasites that invade the body only under unusual circumstances  Meningoencephalitis – Naegleria fowleri Caused by Naegleria fowleri Protozoan infects nasal mucosa from swimming water Penetrates the brain and feeds on brain tissues Primary amebic meningoencephalitis (PAM) Destruction of brain and spinal tissue Results in hemorrhage and coma Death occurs within a week https://els-jbs-prod-cdn.jbs.elsevierhealth.com/cms/attachment/48e227e8-63ff-4636- Meningoencephalitis – Acanthamoeba Caused by Acanthamoeba Invades broken skin, conjunctiva, lungs, and urogenital epithelia At risk are people with traumatic eye injuries, contact lens wearers, and AIDS patients Granulomatous amoebic meningoencephalitis (GAM) Meningoencephalitis similar to Naegleria but a longer infection Acute Encephalitis – Arboviruses Arbovirus: arthropod-borne virus Most often carried by mosquitoes Caused by several different viruses from several families Symptoms range from subclinical to severe Often chills, headache, and fever Progress to mental confusion and coma Prevention: controlling mosquitoes  Acute Encephalitis – Arboviruses West Nile virus Maintained in bird–mosquito–bird cycle Can cause polio-like paralysis and fatal encephalitis West Nile Arbovirus Cases: 2016 https://www.ncbi.nlm.nih.gov/books/NBK544246/bin/transmissionWestNile.jpg  Acute Encephalitis – Arboviruses There are many other viral causes of arboviral encephalitis Eastern equine encephalitis Western equine encephalitis St. Louis encephalitis California encephalitis Heartland virus disease Powassan virus Japanese encephalitis  Subacute Encephalitis – Prions Prion: abnormally folded protein Causes normal proteins (PrPC) in brain tissue to become abnormally folded (PrPSc) Leads to spongiform degeneration Brain becomes porous; spongelike Chronic and fatal Prions are difficult to destroy using standard methods Sterilization of surgical instruments by NaOH with extended autoclaving at 134°C No PrPSc detection test exists for live animals  Subacute Encephalitis – Prions Transmissable spongiform encephalopathies Scrapie – Sheep Chronic wasting disease – Deer and elk Creutzfeldt-Jakob disease – Humans Kuru – Humans (caused by cannibalism) Bovine spongiform encephalopathy (mad cow disease) – Cows https://microbewiki.kenyon.edu/images/3/31/ Rabies Caused by the rabies virus Usually transmitted by saliva of animal bites Rabies virus https://veteriankey.com/wp-content/uploads/2016/08/B9781416061304000203_f020-  Rabies Disease progression Average incubation – 30-50 days Initial symptoms: muscle spasms of mouth and pharynx related to swallowing; hydrophobia Virus multiplies in skeletal muscles and travels through PNS to brain cells, causing encephalitis Almost always fatal; 99.9% mortality rate Rabies Positive Diagnosed from bodily fluids direct using direct fluorescent- fluorescent antibody test -antibody test Prevention Postexposure prophylaxis: vaccine plus immune globulin Vaccine – series of 4 injections over 14 days Immune globulin – antibodies taken from immunized individuals Very little effective treatment Milwaukee protocol – induced coma; minimizes excitability during antiviral drug treatment  Rabies Found globally; mostly due to dog bites In U.S., occurs in bats, skunks, foxes, raccoons, and domestic animals Cases in US Animals – 7000-8000 Humans – 1-6  Tetanus Caused by Clostridium tetani Gram-positive, endospore-forming, obligate anaerobe Grows in deep wounds with anaerobic conditions http://services.epnet.com/getimage.aspx? imageiid=7591  Tetanus Disease Infection causes no inflammation; bacteria do not leave infection site Tetanospasmin neurotoxin Released from killed bacterial cells Enters CNS via blood or peripheral nerves Blocks the relaxation pathway in muscles, causing muscle spasms Jaw muscles affected early (lockjaw) Death occurs from spasms of respiratory muscles https://www.findatopdoc.com/var/fatd/storage/images/_aliases/article_main/media/ images/tetanussymptoms/445546-1-eng-US/TetanusSymptoms.jpg  Tetanus Prevented by vaccination with a tetanus toxoid Stimulates antibodies that neutralize the toxin Booster required every 10 years 40% of US adult population not protected Fewer than 10 cases per year Mortality of 25–50% Treatment with tetanus immune globulin Antibody against toxin Infected tissue removed (debridement) https://www.cdc.gov/tetanus/images/tetanus-  Botulism Caused by Clostridium botulinum Gram-positive, endospore-forming, obligate anaerobe Intoxication comes from ingesting the botulinal exotoxin. Toxin is specific for the synaptic end of the nerve Blocks release of the neurotransmitter acetylcholine, causin