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Introduction to Microbiology

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Introduction to Microbiology Introduction to microbiology Prof. dr hab. Beata M. Sobieszczańska Department of Microbiology University of Medicine • http://www.lekarski.umed.wroc.pl/mikrobiologia • schedules, rules, important information • Consulting hours – teachers are always available for students during consulting hours or classes – apart from consulting hours – you must chase ! • Sick leaves (original) must be shown to the teacher just after an absence but not longer than after two weeks otherwise a sick note will not be honored - a copy of the sick note must be delivered to the secretary office • Class tests – 10 open questions • Terms: 1st, 2nd – if failed commission test from the whole material at the end of semester • Students with the average 4.8 will be released from the final exam • Presence on lectures and classes are obligatory • The final grade from classes is the average of all grades during semester Your best friend in this year: Medical Microbiology by Patrick R. Murray, Ken S. Rosenthal, Michael A. Pfaller Answer questions: • Name important cell wall structures of GP and GN bacteria • What is a role of these structures in human diseases? • Name other than bacterial cell wall structures and explain their role in bacterial pathogenicity • Do you understand the term pathogenicity? • Name five different genera GP and GN bacteria and indicate the colour they have after Gram staining Answer questions: • Name clinically important bacteria producing endospores – why endospores are important? • What is the difference between capsule and glycocalyx layer on GP bacteria? • What is axial filament? What role it plays? What bacteria produce axial filaments? • Name two types of pili and their role in bacterial pathogenicity Most bacteria come in one of three basic shapes: coccus, rod or bacillus & spiral MURRAY 7th ed. chapters: 12 – 16 Immunology: section 3 The COCCI Spherical or oval bacteria having one of several distinct arrangements based on their planes of division The rods and bacilli • rod-shaped bacteria • divide in one plane The spiral Spirals come in one of three forms: • vibrio - a curved or comma-shaped rod • spirillum - a thick, rigid spiral • spirochete - a thin, flexible spiral Spirillum The spirochete Borrelia (arrows) in a blood smear Spirochete Bacteria :unicellular, microscopic, prokaryotic organisms that reproduce by binary fission Prokaryotic cell Simple structure: a) The nuclear body (nucleoid) is not bounded by a nuclear membrane b) It contains one circular chromosome composed of DNA associated with histone- like proteins - prokaryotic cells are haploid c) There is no nucleolus Structurally a typical bacterium usually consists of: • a cytoplasmic membrane surrounded by a peptidoglycan cell wall & maybe an outer membrane • a fluid cytoplasm containing a nuclear region (nucleoid) & numerous ribosomes • often various external structures such as a glycocalyx, capsule, flagella & pili Cytoplasmic membrane Is a fluid phospholipid bilayer imbedded with proteins & usually lacking sterols – exception: mycoplasmas The electron transport system is located in the cytoplasmic membrane Bacterial cell wall • Contains a semirigid, tightknit molecular complex called peptidoglycan • Mycoplasmas & ureaplasmas are the only bacteria that naturally lack a cell wall Peptidoglycan A peptidoglycan monomer consists of two joined amino sugars: N-acetylglucosamine (NAG) N-acetylmuramic acid (NAM) with a pentapeptide coming off of the NAM The types & the order of amino acids in the pentapeptide are almost identical in most bacteria The peptidoglycan The peptidoglycan monomer of monomer of Escherichia coli Staphylococcus aureus Most bacteria can be placed into one of three groups based on their colour after specific staining procedures performed: gram-positive (GP) gram-negative (GN) acid-fast These staining reactions are due to fundamental differences in their cell wall Gram-positive (GP) bacteria They retain the initial dye during the Gram stain procedure & appear purple Common GP bacteria of medical importance include: Streptococcus pyogenes, Streptococcus pneumoniae, Staphylococcus aureus, Enterococcus faecalis & Clostridium species Gram-positive bacteria cell wall structure Gram-negative bacteria (GN) They decolorize during the Gram stain procedure & appear red Common GN bacteria of medical importance include: Salmonella species, Shigella species, Neisseria species, Haemophilus influenzae, Escherichia coli, Klebsiella pneumoniae, Proteus species & Pseudomonas aeruginosa Gram-negative bacteria cell wall structure Endospores: Clostridium and Bacillus Structures on the cell wall a) Glycocalyx - is usually a viscous polysaccharide or polypeptide slime layer in GP cocci (Staphylococci & Streptococci) b) Capsule - a viscous thick covering surrounding a cell composed of polysaccharides Structures outside the cell wall Flagella - a rotating appendages arising from the bacterial surface and used for locomotion (axial filaments in spiral bacteria) c) Pili (fimbria) - a tubular protein structure extending from a bacterial surface used for attachment to environmental surfaces or cells Flagellar Arrangements Pili (fimbria) They are found in: - virtually all Gram-negative bacteria - not in many Gram-positive bacteria Adhesive tip of bacterial The pilus has: pili binding to host cell receptors • a shaft composed of a protein called pilin • adhesive tip structure having a shape corresponding to that of specific glycoprotein or glycolipids receptors on a host cell Pili (fimbriae) There are two basic types of pili: 1) short attachment pili (fimbria) - quite numerous 2) long conjugation pili ("F" or sex pili) - very few in number Conjugation (sex) pilus Effect of oxygen on bacteria Culture media Hemolytic activity on blood agar Summary • Shapes and arrangements of bacteria: cocci, rods/bacilli, spiral. These may grow singly, in clusters or in chains • Gram-positive bacteria are dark violet and Gram- negative bacteria are pink /red • The Gram reaction is related to the structure of the cell envelope • Peptidoglycan: responsible for shape and strength of the cell wall of bacterium • Teichoic acids in Gram-positives • Lipopolysaccharide (endotoxin, LPS) in Gram- negative outer membrane • Capsules, slime layers, glycocalyx: role in adhesion/biofilm and in protection (anti-phagocytic) • Surface appendages: flagella = motile, fimbriae/pili = attachment • Sporulation in Bacillus and Clostrdium (spores) survival in hostile environment Pathogenesis of infections • Adhesion (pili, proteins)/invasion (invasins) = spreading in tissues • Immune system evasion (e.g. survival in macrophages) • Toxin & enzymes production (cells & tissue damage) • Multiplication at the site of infection (biofilm formation) • Stimulation of the immune response Next lecture and classes: staphylococci and streptococci – prepare from Murray chapters: 18, 19, 20 Thank you for your attention .
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