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Microbiology

Microbiology. Microbiology is the study of:. Bacteria Viruses Protozoa Fungi. Importance of studying microbiology. Welfare Morbidity and mortality Economics Productivity Public health Transmission to humans Genetic engineering Cloning. Procaryote v Eucaryote.

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Microbiology

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  1. Microbiology

  2. Microbiology is the study of: • Bacteria • Viruses • Protozoa • Fungi

  3. Importance of studying microbiology • Welfare • Morbidity and mortality • Economics • Productivity • Public health • Transmission to humans • Genetic engineering • Cloning

  4. Procaryote v Eucaryote

  5. Bacterial morphology, structure and function

  6. Morphology Bacteria come in all shapes and sizes

  7. Morphology

  8. Bacterial Structure

  9. Bacterial Nucleoid • Single closed circle of DNA ~ 1000 mm in length, some bacteria have 2 nucleoids • Highly condensed • Not enclosed by membrane • Not complexed with histones but associated with histone like proteins • Microscopically appears as amorphous mass roughly at centre of cell • Separation of chromosomes does not involve mitotic apparatus • Plasmids may be present (extrachromosomal DNA)

  10. 30S 40S 50S 60S Ribosomes PROCARYOTES EUCARYOTES Svedberg (S) units (sedimentation coefficient) Polysomes (strings of ribosomes) 70S 80S Composed of proteins and RNA (rRNA). Site of translation (protein synthesis) Sensitivity to antibiotics

  11. Bacterial Cytoplasmic Membrane • Phospholipid bilayer with associated protein • Protein content very high ~ 70% • Usually lack sterols Functions of the Cytoplasmic Membrane • Selectively permeable membrane • Freely permeable to water, gases and small hydrophobic molecules • Specific transport proteins for nutrients and ions • Electron transport and oxidative phosphorylation • Synthesis of macromolecules • Sensing environment • Chromosome segregation

  12. Peptidoglycan • Unique to bacteria. • Provides strength and rigidity to cell. • Protects cells from variations in external osmolarity. • Polymer of NAG-NAM-tetrapeptide. • Unique amino acids D-alanine, D-glutamate, diaminopimelic acid (DAP). • Cross-linked via peptide chain. • Peptidoglycan layer much thicker in gram positive than gram negative bacteria.

  13. NAM NAG NAM NAM NAG NAM NAG NAM NAG NAM NAM NAG NAM NAG NAG NAM NAG NAM NAM NAG NAM L-alanine NAG NAG NAM D-glutamate NAG NAM NAG Diaminopimelic acid NAM D-alanine NAG D-alanine NAG Diaminopimelic acid NAM D-glutamate NAG L-alanine N-acetylglucosamine N-acetylmuramic acid NAM NAG Peptidoglycan

  14. Gram Stain For descriptive purposes bacteria grouped into 4 main characteristics:- • Shape • Atmospheric requirements for respiration • Presence of spores • Gram stain – Important for grouping bacteria of medical and veterinary importance • Gram stain - Depends on cell wall structure, amount of peptidoglycan and presence of teichoic acids • Gram positive and Gram negative bacteria have different susceptibilities to antibiotics

  15. Gram Stain Gram positive Gram negative Outer membrane Cell wall Cell (inner) membrane

  16. Gram positive cell wall

  17. Gram negative cell wall

  18. Outer Membrane • Present outside the cell wall in gram negative bacteria. • Bilayer, phospholipid in inner leaflet and LPS in outer leaflet. • Surface O side chains are charged and provide a barrier to hydrophobic substances. • Lipid membrane excludes hydrophilic compounds. • Outer membrane proteins allow essential nutrients access through outer membrane. • Porins: trimers that form non-specific pores. • Specific receptors for: • Iron complexed to siderophores. • Sugars, eg, maltose. • Vitamins, eg, B12.

  19. Lipopolysaccharide • Unique, found only in Gram negative bacteria • 3 regions: Lipid A; Core, O side chain Lipid A O side-chain LPS LOS Core • O side chain • Long in enteric bacteria, eg, Salmonella. Lipopolysaccharide (LPS) • Short in some respiratory pathogens, eg, Haemophilus. Lipooligosaccharide (LOS) • Long O side chain acts as a barrier to toxic hydrophobic compounds and may shield OMP from bacteriophages, bacteriocins and antibodies • Very immunogenic, highly variable

  20. Not all bacteria stain by the Gram Stain Mycoplasma No cell wall Mycobacteria Waxy coat

  21. Acid Fast Bacteria • Gram positive-like • Tough, waxy cell wall • Resists staining (requires heating) and decolourising (even by acid) • Mycobacteria • Contain mycolic acid and wax D • Very acid fast • Some pathogenic species extremely slow growth rate • Actinomyces, Nocardia, Streptomyces • Filamentous, branching bacteria • Less acid fast

  22. Mycobacterial cell envelope

  23. Mycoplasmas • Mollicutes. Smallest free-living organisms • Lack cell wall, pleomorphic shape • Contain cholesterol in cell membrane • Small genome (600 - 800 genes), E.coli 4,000 genes • Cause infections of mucosal surfaces

  24. Important Structures Spores Flagella Pili (Fimbriae) Capsules

  25. Capsules Usually acidic polysaccharides B.anthracis – Poly D-glutamic acid Anti-phagocytic. Anti-capsular antibodies V.imp in immunity Prevents dessication

  26. Flagellated bacterium • Flagellum main function for bacterial motility • Made of globular protein flagellin • Bound via motor unit, energy provided by ion gradient across the membrane converted into rotary movement • Motility per se is not necessarily a pathogenic determinant but may be very important in pathogenesis for some bacteria e.g. Campylobacter species • Used for antigenic typing – Salmonella

  27. Arrangement of flagella Monotrichous: A single flagellum at one end Ampitrichous: one or more flagella at each end Lophotrichous: two or more flagella at one or both ends Peritrichous: flagella surrounding the cell

  28. Fimbriae\Pili • Long, thin structures • Mediate attachment to eucaryotic cells, eg, K88 of E.coli • Bind carbohydrate residues: Lectins • Composed of protein subunits (pilin) • Specialised pilins at tip may act as adhesin • Expression affected by environmental conditions, eg, not expressed at low temperature • virulence factor • Sex pili: • Involved in conjugation • Conjugative pilus • Present on ‘male’ cells and attach to ‘female cells’ • Genes carried on conjugative plasmids

  29. Endospores • Produced by Bacillus sp and Clostridium sp (Gram positives) • Formed whenconditions are unfavourable for survival of bacteria • Form inside the bacterial cell and released when bacteria lyses • Germinate to vegetative cells when conditions are move favourable • Extremely resistant to heat, desiccation, extremes of pH • Have a low water content

  30. Cortex Exosporium Core wall Spore coat DNA Ribosomes Core Endospore structure

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