General Bacteriology Past Paper PDF 2023-2024

General Bacteriology MDP 10208 Siti Fairouz Ibrahim, PhD 2023/2024 Specific instructional objective Students should be able to: 1. define bacteria 2. describe briefly the major structures and their functions 3. list and describe briefly their morphological forms 4. describe br...

General Bacteriology MDP 10208 Siti Fairouz Ibrahim, PhD 2023/2024 Specific instructional objective Students should be able to: 1. define bacteria 2. describe briefly the major structures and their functions 3. list and describe briefly their morphological forms 4. describe briefly bacterial metabolism, growth, and reproduction 5. list common diseases and the bacterial agent causing them Bacteria A microscopic unicellular organism of various shapes and sizes a procaryotic cell Carry metabolic activities to increase its size One cell enlarges, divide into 2 equal parts Replication precedes division Reproduce by binary fission Size o 0.5 – 1um broad o 0.5 – 8um long The sizes of microorganisms Bacterial distribution in the environment Bacteria are procaryotic organisms Procaryotes are found in: the habitats where eucaryotes live natural environments considered too extreme or inhospitable (hottest, coldest, driest, etc.) for eucaryotic cells where eucaryotes and procaryotes live together, there may be mutualistic / symbiotic associations that allow both to survive the organelles of eucaryotes (mitochondria and chloroplasts) are thought to be remnants of bacteria that are invaded by primitive eucaryotes in the evolutionary past numerous types of eucaryotic cells that exist today are inhabited by endosymbiotic procaryotes only a few bacteria are agents of disease Normal flora bacteria and fungi that are permanent residents of certain body sites especially: o Skin o Oropharynx o Colon o vagina viruses and parasites are usually not considered normal flora o although they can be present in asymptomatic individuals often referred to as commensals o organisms that derive benefit from another host but do not damage that host Remember at least 3 Medically Important Normal Flora Location Important Organisms Less important organisms Staphylococcus aureus, Corynebacterium, streptococci, Skin Staphylococcus epidermidis Pseudomonas aeruginosa, Propionibacterium, Candida albicans Nose Staphylococcus aureus S. epidermidis, Corynebacterium (diphtheroids), streptococci Mouth Viridans streptococci Streptococci, Eikenella corrodens Dental Streptococcus mutans Prevotella intermedia, Porphyromonas gingivalis plaque Gingival Bacteroides, Fusobacterium, crevices streptococci, Actinomyces Streptococcus pyogenes, Streptococcus pneumoniae, Neisseria Throat Viridans streptococci species, Haemophilus influenza, S. epidermidis Bifidobacterium, Eubacterium, Fusobacterium, Lactobacillus, Bacteroides fragilis, Colon aerobic gram-negative rods, Enterococcus faecalis, streptococci, Escherichia coli Clostridium Lactobacillus, E. coli, group B Streptococci, gram-negative rods, B. fragilis, Corynebacterium, C. Vagina streptococci albicans Urethra S. epidermidis, Corynebacterium, streptococci, E. coli Importance in medicine provide convenient laboratory models for infectious diseases production of antibiotics against infectious diseases bacterial components for vaccine identification microbial pathogen will permit the selection of pharmacologic treatment specifically directed toward their eradication Koch’s postulate (1884) The organism must be 1. constantly found in every case of the disease and absent from healthy hosts 2. isolated and grown outside the host eg in pure culture on artificial media 3. able to reproduce the disease in healthy but susceptible hosts 4. re-isolated from the susceptible hosts in no.3 Demonstrating the pathogenicity of a microorganism via Koch’s postulate Structures of bacteria Cell Envelope made up of two or three layers: 1. the interior cytoplasmic membrane 2. the cell wall 3. in some species of bacteria -- an outer capsule Bacterial capsule Capsule Found in some bacteria made up of polysaccharides (complex carbohydrates) prevent the bacterium from drying out protect from phagocytosis (engulfing) a major virulence factor in the major disease-causing bacteria o eg in Escherichia coli and Streptococcus pneumoniae Structures of bacteria Cell Wall contain peptidoglycan, a protein-polysaccharide molecule gives the cell its shape and protects it from the environment. helps to anchor appendages like the pili and flagella, prevent the cell from bursting due to the osmotic pressure is one of the most important factors in bacterial species analysis and differentiation Other components include: differences between -mcq o Lipoteichoic acids (LTA) - only in Gram-positive bacteria -seq o Lipopolysaccharides (LPS) - only in Gram-negative bacteria Peptidoglycan Glycan portion - alternating NAM and NAG molecules Peptide linkage - rows of NAG and NAM are linked by polypeptides polypeptide cross-bridges may vary but they always have a tetrapeptide sidechain penicillin interferes with peptidoglycan synthesis Gram positive bacteria Gram negative bacteria Structures of bacteria Cytoplasmic Membrane a layer of phospholipids and proteins encloses the interior part regulates the flow of materials in and out of the cell is highly organized and asymmetric; having two sides o each side is different and has different function is dynamic, constantly adapting to different conditions. Cytoplasm is where the functions for cell growth, metabolism, and replication are carried out is a gel-like matrix composed of water, enzymes, nutrients, wastes, and gases contains cell structures such as ribosomes, a chromosome, and plasmids and other cellular components Structures of bacteria Nucleoid not a membrane bound nucleus a region of the cytoplasm where the strands of chromosomal DNA are found. most bacteria have a single, circular chromosome that is responsible for replication chromosome a single, continuous strand of DNA Only the chromosome has the genetic instructions for initiating and carrying out cell division, or binary fission Structures of bacteria plasmids are small, genetic structures made of a circular piece of DNA replicate independently of the chromosome are not involved in reproduction not essential for survival, but give bacteria a selective advantage Plasmids are passed on to other bacteria through two means: production of antibiotic 1. Most types - passed on to daughter cells during binary fission 2. Other types - form a tubelike structure called pilus passes copies of the plasmid to other bacteria during conjugation allow transmission of special properties, such as o antibiotic drug resistance o resistance to heavy metals o virulence factors necessary for infection of animal or plant hosts useful tools in molecular biology and genetic engineering Structures of bacteria Flagella (singular, flagellum) made up of protein are hairlike structures that provide a means of locomotion not all bacteria have them the flagella beat in a propeller-like motion to help the bacterium move: 1. toward nutrients Monotrichous 2. away from toxic chemicals 3. in the case of the photosynthetic Lophotrichous cyanobacteria; toward the light. Amphitrichous Peritrichous  Structures of bacteria (made up proteins) Pili (singular, pilus) small hair-like projections emerging from the outside cell surface fimbriae and pili are interchangeable terms made up of protein Many bacterial species have pili o assist in attachment to host cells and surfaces, such as teeth, intestines, and rocks o without pili, many bacteria lose their specialized pili are used for ability to infect because they're conjugation unable to attach to host tissue o two bacteria can exchange fragments of plasmid DNA Structures of bacteria Ribosomes Made up of proteins and rRNA translate the genetic code from the molecular language of nucleic acid to that of amino acids (proteins) o Proteins perform all the functions of cells and living organisms bacterial ribosomes are similar to those of eukaryotes o but are smaller and have a slightly different composition and molecular structure never bound to other organelles free-standing structures distributed throughout the cytoplasm sufficient differences between bacterial and eukaryotic ribosomes o some antibiotics will inhibit the functioning of only bacterial ribosomes, but not of eukaryote's Structures of bacteria Endospore made up of mainly chromosomal nucleic acid and spore coat found almost exclusively in Gram-positive bacteria o however, only some species of Gram-positive bacteria can form endospore two important pathogenic genera that are capable of endospore formation are Bacillus and Clostridium allows the bacteria to survive harsh environmental conditions the process of sporulation begins when vegetative (or actively growing) cells exhaust their source of nutrients in the spore form, the organisms are very resistant to heat, radiation and drying and can remain dormant for hundreds of years once conditions are favorable for growth, the spores can germinate and return to the vegetative state micro.magnet.fsu.edu/cells/bacteriacell.html Metabolism the total sum of the chemical processes that occur in living organisms, resulting in growth, production of energy, elimination of waste material bacteria exhibit an extremely wide variety of metabolic types the metabolic traits has been used to define their taxonomy o but these traits often do not correspond with modern genetic classifications bacterial metabolism is classified into nutritional groups on the basis of three major criteria: o the kind of energy used o the source of carbon o the electron donors used Mechanisms of generating metabolic energy for bacterial growth Heterotrophy is the use of an organic compound as a source of carbon (food source) and energy o animals, fungi, protozoa, many bacteria are heterotrophs Lithotrophy is the use of an inorganic compound as a source of energy eg Nitrobacter, Sulfolobulus Phototrophy – light driven ATP synthesis eg Cyanobacteria Autotrophic CO2 fixation is self-feeding in that CO2 is converted (fixed) and used as a source of carbon for growth eg photosynthetic bacteria Metabolism Respiration results in the complete oxidation of the substrate by an outside electron acceptor. Metabolic components needed: o Glycolysis o tricarboxylic acid (TCA) cycle (citric acid cycle or Kreb's cycle) o electron transport system (ETS) o outside electron acceptor ("outside” - not internal to the pathway) o ATPase enzyme (ATP synthetase) Fermentation is metabolism in which energy is derived from the partial oxidation of an organic compound using organic intermediates as electron donors and electron acceptors o No outside electron acceptors are involved o no membrane or electron transport system is required o all ATP is produced by substrate level phosphorylation Model of Aerobic Respiration Metabolism respiratory organisms use chemical compounds to synthesize ATP and drive metabolism many microorganisms produce their energy using aerobic respiration where oxygen is used as the electron acceptor o aerobic microorganisms / aerobes other microorganisms are able to survive in environments lacking oxygen by performing anaerobic respiration (eg in fermentation) o anaerobic microorganisms / anaerobes anaerobes use other inorganic compounds, such as nitrate or sulfate as electron acceptors Metabolism anaerobic respiration/fermentation is typically slower and less efficient than aerobic respiration o fermentation process generates metabolic by-products (such as ethanol in brewing) as waste facultative anaerobes are able to perform either aerobic respiration or anaerobic respiration depending on the oxygen content of their environment o since aerobic respiration is more efficient, facultative anaerobes will perform aerobic respiration in the presence of oxygen in their environment Oxygen Requirements of Bacteria anaerobic bacteria little amount of oxygen phagotetif anaerob aerobic bacteria erogoterant bacteria -req oxygen Atmospheric growth requirements A. Strict/obligate aerobes requires atmospheric oxygen eg Pseud. aeruginosa, Mycobacterium tuberculosis, Norcadia B. Strict/obligate anaerobes will not tolerate oxygen eg Bacteroides fragilis, most Clostridium species C. Facultative anaerobe grows best aerobically but can grow anaerobically eg. Staphylococcus spp., E. coli, K. pneumoniae, etc Atmospheric growth requirements D. Aerotolerant anaerobe anaerobic but tolerates exposure to oxygen eg Clostridium perfringens E. Microaerophilic requires or prefers reduced oxygen levels eg. Campylobacter spp., Helicobacter spp. F. Capnophilic requires or prefers increased CO2 levels eg. Neisseria spp. Growth and reproduction the size increase of bacteria (cell growth) and their reproduction by cell division are tightly linked bacteria grow to a fixed size and then reproduce through binary fission, a form of asexual reproduction under optimal conditions, bacteria can grow and divide extremely rapidly, and bacterial population can double as quickly as every 9.8 minutes in cell division, two identical clone daughter cells are produced Binary fission of a bacterial cell replication of the chromosome starts at the origin attached to the cell wall, near the midpoint of the cell Replication occurs bidirectionally around the chromosome, as the cell elongates New replicating forks can start before the first cell division takes place o this phenomenon allows an extremely rapid rate of reproduction Growth and reproduction In the laboratory, bacteria are usually grown using solid or liquid media Solid growth media such as agar plates are used to isolate pure cultures of a bacterial strain liquid growth media are used when measurement of growth or large volumes of cells are required stirred liquid media is used to grow an even cell suspension, making the cultures easy to divide and transfer o however, isolating single bacteria from liquid media is difficult the use of selective media (media with specific nutrients added or deficient, or with antibiotics added) can help identify specific organism  Bacterial colonies Various bacterial colonies growing in a petri dish containing nutrients. Hans Knoll Institute, Jena, Germany Bacterial colonies on blood agar Bacteria was cultured for 24 hours, 37°C in an aerobic atmosphere Escherichia coli Pseudomonas aeruginosa Staphylococcus aureus (colony surrounded by a zone of beta- hemolysis) Staphylococcus epidermidis Growth and reproduction in natural environments nutrients are limited o bacteria cannot continue to reproduce indefinitely Some organisms can grow extremely rapidly when nutrients become available o algal and cyanobacterial blooms occur in lakes in summer Other organisms have adaptations to harsh environments o antibiotics produced by Streptomyces inhibit the growth of competing organisms in nature, many organisms live in communities eg biofilms o allow for increased supply of nutrients and protection from environmental stresses o allow for syntrophy: phenomenon involving one species living off the metabolic products of another species Bacterial growth curve has high biosynthesis rates, as proteins necessary for rapid growth are produced Four phases of bacterial growth curve 1. lag phase - slow growth period has high biosynthesis rates, as proteins necessary for rapid growth are produced 2. logarithmic (log) / exponential phase nutrients are metabolised at max. speed until nutrient is depleted Varies as doubling time of different bacteria differs eg S. typhi – 20 min 3. stationary phase - caused by depleted nutrients the cells reduce their metabolic activity and consume non-essential cellular proteins a transition from rapid growth to a stress response state increased expression of genes involved in DNA repair, antioxidant metabolism and nutrient transport 4. death phase death > growth Tocxin build up: harmful for bacterial the lack of nutrients or accumulation of waste products kills the cells Common diseases pathogenic bacteria are parasites o a major cause of human death and disease o cause infections such as tetanus, typhoid fever, diphtheria, syphilis, cholera, foodborne illness, leprosy and tuberculosis a pathogenic cause for a known medical disease may only be discovered many years after o eg Helicobacter pylori and peptic ulcer disease also important in agriculture o cause leaf spot, fire blight and wilts in plant o mastitis, salmonella and anthrax in farm animals each species of pathogen has a characteristic spectrum of interactions with its human hosts o some organisms eg Staphylococcus or Streptococcus, can cause skin infections, pneumonia, meningitis or even sepsis that can result in death o yet these organisms are part of the normal human flora Common diseases Other organisms invariably cause disease in humans, such as the Rickettsia o obligate intracellular parasites able to grow and reproduce only within the cells of other organisms o One species of Rickettsia causes typhus, while another causes Rocky Mountain spotted fever Chlamydia, another genus of obligate intracellular parasites, contains species that can cause o pneumonia o urinary tract infection o may be involved in coronary heart disease some species are opportunistic pathogens and cause disease mainly in people suffering from immunosuppression or cystic fibrosis o Pseudomonas aeruginosa o Burkholderia cenocepacia o Mycobacterium avium From Wikipedia Thank you!