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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 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
morphology
Morphology

Bacteria come in all shapes and sizes

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
slide17

Gram Stain

Gram positive

Gram negative

Outer membrane

Cell wall

Cell (inner) membrane

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
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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