MIC Lecture Notes (3) - Bacterial Morphology, Growth, and Pathogenesis PDF

L1 - Bacterial Morphology Diff types of Microorganisms: Bacteria: small single-celled organisms Viruses: infective agent Fungi: group of spore-producing organisms Protozoa: polyphyletic group of single-celled eukaryotes Archaebacteria: asexual, prokaryotes that live in extr...

L1 - Bacterial Morphology Diff types of Microorganisms: Bacteria: small single-celled organisms Viruses: infective agent Fungi: group of spore-producing organisms Protozoa: polyphyletic group of single-celled eukaryotes Archaebacteria: asexual, prokaryotes that live in extreme environments Prions: protein that can trigger normal proteins in the brain to fold abnormally Algae: diverse group of aquatic organisms that have the ability to conduct photosynthesis Slime moulds: type of protist that aggregates into colonies Prokaryotic vs Eukaryotic cells Bacteria (Prokaryotic): - Unicellular - absence of nucleus - DNA chromosome is circular - Ribosome size is smaller - Absence of mitochondria - Plasmid is present Fungi (Eukaryotic): - Multicellular - Presence of Nucleus - Linear DNA chromosome - Ribosome size is bigger - Presence of Mitochondria - Plasmid present in some Bacterial Morphology Shape: Cocci (Spherical), Bacilli (Rod), Spiral (Flexible) Arrangement: Single, Pairs, Clusters, Chains Size: Width 0.2-1.2 um, Length 0.4-14 um Staining: Gram stain (positive- negative), Acid fast stain, Silver stain Appendages: Flagella/Flagellum : elongated protein filament cylinders, for motility  Pilus/Fimbriae: appear as tiny hairs around a bacterium; mediate adherence of bacteria to cell surface, sex pilus forms during conjugation Capsule: made of polysaccharides, protection against phagocytosis/virulence factors Slime (S) layer: loose polysaccharides; adherence to surfaces & biofilm formation Periplasm: space between cytoplasmic and outer membrane, accumulates components exiting gram negative Cell Wall: rigid structure made up of peptidoglycan, serves as shape, support & protection against osmotic pressure damage Cytoplasmic membrane: phospholipid bilayer sac with embedded proteins, serves as site of oxidative & transport enzymes Plasma Membrane: for respiration, photosynthesis & synthesis of lipids and cell wall constituents L2 - Bacterial Growth & Physiology Kinds/Types of Microorganisms Probiotics: normal bacterial flora that are helpful for human digestion and regularity, examples: Lactobacillus acidophilus, Bifidobacteria, and Bacillus coagulans Symbiotics: require humans to survive but provide biological benefits to humans in return Opportunists: potential pathogens that would not normally inhabit the body but take advantage of opportunity. These opportunities include a weakened immune response etc. example: Pseudomonas aeruginosa and Staphylococcus epidermidis Pathobionts: benign, endogenous microorganism. Potentially pathogenic microorganism that may cause disease when overgrowth occurs. C difficile is an excellent example Bacterial Growth Factors: Temperature Psychrophiles: cold lovers, with an optimum of 15oC or lower and a growth range of -20 C to 20 C Psychrotrophs: cold tolerant microbes have a range of 0-35oC, with an optimum of 16oC or higher. Mesophiles: A group of bacteria that grow and thrive in a moderate temperature range between 68°F (20°C) and 113°F (45°C), growth optima of 37oC Thermophiles: heat lovers, typically have a range of 45-80oC, and a growth optimum of 60oC  Hyperthermophiles: microbes that like very hot things. These microbes have a growth optima of 88-106oC, a minimum of 65oC and a maximum of 120oC Aerobes can only survive in the presence of oxygen through an elaborate system of defenses. Without these defenses, key enzyme systems in the organisms fail to function, and the organisms die. Obligate anaerobes, which live only in the absence of oxygen, do not possess the defenses that make aerobic life possible and, therefore, can not survive in air. The tolerance to oxygen is related to the ability of the bacterium to detoxify superoxide and hydrogen peroxide, produced as a byproduct of aerobic respiration. Obligate Aerobe: need oxygen for growth Obligate Anaerobe: does not need oxygen for growth Facultative Anaerobe: can tolerate anaerobic conditions, but improves with oxygen Microaerophiles: need lower than normal level of oxygen for growth Aerotolerant Anaerobes: can grow in the presence or absence of oxygen, exhibiting no preference.  Bacterial Growth Curve Lag Phase: bacteria mature and adapt to the growth environment, reproduction is slow Exponential growth phase: rapid bacterial growth, proportional creation of new cells, phase continues until bacteria run out of resources (physical space/nutrients) Stationary phase: physiologic limitation to bacteria growth has been reached, number of new bacteria appearing and dying is roughly same Death Phase: period where bacterial population diminishes/dies L3 - Bacterial Pathogenesis Each person contains 23,000 human genes and over 600,000 microbial genes. Therefore, the human component accounts for less than 4% of the whole hologenome. Pathogen: microorganisms that cause disease Reservoir: place in the environment where a pathogen lives, replicates and thrives Portal of Exit: any route that the pathogen can leave the reservoir Mode of Transmission: how a pathogen can be transferred from one person, object, or animal, to another Portal of Entry: any route that pathogen uses to enter the body Susceptible Host: the person who can potentially get infected ex: old age, person who has weak immune system etc. Who is the Carrier of Infection? An apparently healthy individual Harboring a pathogenic organism No clinical manifestations Can transmit this organism to others Not known to public and are not easily detected Not restricted to bed Carry the organism in the interepidemic periods Most host-parasite partnerships have three basic variables that determine their outcome The infectious dose is the number of pathogens that are required to infect a host, and it varies significantly across pathogen species. The infectious dose depends mainly on the bacterial virulence factors Virulence Factors: Adherence factors: - Specialized structures, Pili: (Neisseria gonorrhoeae and E. coli) - Produce adherent substances/biofilm formation: Staphylococcus epidermidis Invasion Factors: - Enzymes: Streptococcus pyogenes  - Antiphagocytic factors: Capsule and cell wall proteins of Gram Positive cocci, such as the M protein of Streptococcus pyogenes Bacterial Toxins - Exotoxins: heat-labile proteins (heat sensitive) - Endotoxin: heat stable lipopolysaccharide produced at the time of cell death L4 - Bacterial Genetics and Virulence Factors CENTRAL DOGMA  Transformation: a bacterium takes in DNA from its environment, often DNA that's been shed by other bacteria viruses that infect bacteria move short pieces of chromosomal DNA from one bacterium to another "by accident." The viruses that infect bacteria are called bacteriophages. Conjugation: how bacteria join together, DNA is transferred from one bacterium to another. After the donor cell pulls itself close to the recipient using a structure called a pilus, DNA is transferred between cells. In most cases, this DNA is in the form of a plasmid.  Transposable elements are chunks of DNA that "jump" from one place to another. They can move bacterial genes that give bacteria antibiotic resistance or make them disease-causing. Generalized Transduction Generalized transduction is swapping of genes, through homologous recombination, into the chromosome of recipient progeny. Specialized Transduction Specialized transduction is an excisional process. A temperate bacteriophage infects a bacterium and transfers viral DNA, which incorporates into the host DNA, forming a prophage. The viral DNA becomes dormant (doesn’t actively replicate or cause lysis of host bacterial DNA) and is passed on to daughter cells