Lecture 13: Bacteria structure, growth and taxonomy

What are bacteria

• Unicellular, free-living microorganisms

• Taxonomically in bacterial domain: prokaryotes, unpaired chromosome with no nucleus, opposed to eukaryotes

• Kingdom - Protista

Taxonomic ranks of procaryotae (kingdom) to species

Binomial system of bacteria

Genus + Species

Staphylococcus aureus

• Staphule (bunch of grapes)

• Kokkos (berry)

• Aureus (golden)

Why is bacterial taxonomy important?

• Handling information - storage and retrieval

• Learning - diverse organisms

• Communication - of information about bacteria

• Identification - of unknown bacteria

• Evolution - allows epidemiological data to be understood

Prokaryote Vs Eukaryote protist

Typical bacterial cell

Morphological features of Clostridium difficile

• Cell survival in adverse conditions

• Desiccation, heat, starvation

• Gram +ve bacteria

• Capsule/ glycocalyx (loosely bound and amorphous)

Features of flagella

• Cell motility

• 1-20, can be peritrichous or polar

• Coiled in structure

• Protein (flagellin)

• Anchored in bacterial membranes

• Chemotaxis

Fimbriae (pili) features

• Up to 100+

• Perithrichous

• Not coiled

• Protein (pilin)

• Adherence

Bacterial growth requirements

Physical characteristics - Sensitive to gas/ temp./ water/ pH/ light/ osmolarity

Nutritional requirements - carbon source, nitrogen source, inorganic salts, organic compounds

Phenotypic characteristics of bacteria

Macroscopic/ microscopic

Biotyping vs serotyping

Categorising organisms by the way they respond to biochemical tests, grouping by the presence of a specific set of antigens

Antibiogram patterns

Categorise by response to antibiotics (Abx)

Pyocin vs Phage

Pyocin - toxins produced

Phage - ability to be infected by virus (typing)

Macroscopic (growth on agar medium)

Macroscopic : texture, appearance, pigmentation and optical density

Nutrient agar colony morphology

Muller-Hinton agar

Haemolysis on blood agar

Microscopic: Shape/ arrangement/ size and staining characteristics

Shape + Examples

Microscopic morphology - arrangement

Gram staining

Differentiates bacteria on basis of their cell wall structure

Positive - thick cell wall

Negative - thin cell wall

Gram positive vs negative stages

Crystal violet

Grams Iodine

Decolouriser

Safranin red

Staph aureus vs E.coli, which is Gram+ve and -ve?

Common gram negative bacillus

• Escherichia Coli

• Klebsiella pneumoniae

• Pseudomonas aeruginosa

• Haemophilus influenzae

Gram positive coccus

• Staphylococcus aureus

• Streptococcus pyogenes

Gram negative diplococcus

• Neisseria meningitidis

• Neisseria gonorrhea

Gram +ve vs Gram -ve cell envelope

Lipid bilayer

Two parallel phospholipid cell membranes → lipid bilayer, polar phosphate groups are on outisde, non polar lipid chains on inside

Gram +ve vs Gram -ve cell envelope image

What are the functions of the cell wall?

• Maintain rigidity and cell shape/ structure

• Maintain osmoalroty

• Survival

• Cell division

Bacterial cell wall synthesis

• Peptidoglycan precursor synthesised inside cell

• Exported across cell membrane (blocked by Abx bacitracin)

• A site is created in the existing wall by enzymes action

• Cell grows

Cell wall structure

Mycobacterium cell wall

• Covalently attached to arabinogalactan polymer

• Mycolic acid waxy coat - lipids

• Poor gram stain

• Acid fast (zeihl-Neelsen stain) - carbolfuchsin

Mycoplasma cell wall

• No cell wall

• Cell membrane contains steroids

Cell wall synthesis

Antibiotics such as penicillin, vancomycin

Capsules

Vaccines eg strep. Pneumoniae

Cell membranes

Antibiotics such as polymoxin and vaccines

Ribosomes

Antibiotics eg gentamicin/ tetracyclines