Microbiology
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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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Microbiology

Microbiology


Microbiology is the study of

Microbiology is the study of:

  • Bacteria

  • Viruses

  • Protozoa

  • Fungi


Importance of studying microbiology

Importance of studying microbiology

  • Welfare

    • Morbidity and mortality

  • Economics

    • Productivity

  • Public health

    • Transmission to humans

  • Genetic engineering

    • Cloning


  • Microbiology

    Procaryote v Eucaryote


    Bacterial morphology structure and function

    Bacterial morphology, structure and function


    Morphology

    Morphology

    Bacteria come in all shapes and sizes


    Morphology1

    Morphology


    Bacterial structure

    Bacterial Structure


    Bacterial nucleoid

    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)


    Ribosomes

    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


    Bacterial cytoplasmic membrane

    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


    Peptidoglycan

    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.


    Peptidoglycan1

    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


    Gram stain

    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


    Microbiology

    Gram Stain

    Gram positive

    Gram negative

    Outer membrane

    Cell wall

    Cell (inner) membrane


    Gram positive cell wall

    Gram positive cell wall


    Gram negative cell wall

    Gram negative cell wall


    Outer membrane

    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.


    Lipopolysaccharide

    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


    Not all bacteria stain by the gram stain

    Not all bacteria stain by the Gram Stain

    Mycoplasma

    No cell wall

    Mycobacteria

    Waxy coat


    Acid fast bacteria

    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


    Mycobacterial cell envelope

    Mycobacterial cell envelope


    Mycoplasmas

    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


    Important structures

    Important Structures

    Spores

    Flagella

    Pili (Fimbriae)

    Capsules


    Capsules

    Capsules

    Usually acidic polysaccharides

    B.anthracis – Poly D-glutamic acid

    Anti-phagocytic. Anti-capsular antibodies V.imp in immunity

    Prevents dessication


    Flagellated bacterium

    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


    Arrangement of flagella

    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


    Fimbriae pili

    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


    Endospores

    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


    Endospore structure

    Cortex

    Exosporium

    Core wall

    Spore coat

    DNA

    Ribosomes

    Core

    Endospore structure


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