9. bacteria structure growth and taxonomy Flashcards
Taxonomic ranks
Kingdom
Division
class
family
genus
species
bacteria nomenclature
binomial: genus+species
why is bacterial taxonomy important?
handling info
learning
communication
identification: unknown
evolution
how are bacteria classified
•Phenotypic characteristics
–Morphology: Macroscopic, Microscopic
–Biotyping – biochemical tests
–Serotyping
–Antibiogram patterns
–Pyocin/Phage typing
•Genotypic characteristics
–%G+C ratios
–DNA hybridisation
–Nucleic acid sequence analysis eg MLST
–Chromosomal DNA fragment analysis
–Ribotyping
bacteria classification: macroscopic
growth on agar medium: Shape, Margin, Elevation, Size
–Texture
–Appearance
–Pigmentation
–Optical density
•Opaque/translucent
microscopic classification
morphology of single cells
shape, arrangment, size, staining characteristics
morphology of staphyloccoci
cocci (round), clusters (grapes)
morphology of streptococci
coccus: round
chains
morphology of bacilli
rods
why are gram stains used as a first line for diagnoses of bacterial infections?
the result can be definitive for genus of bacterium
gram +ve: thick cell wall
gram -ve: thin cel wall
function of a cell wall
•Maintain rigidity and cell shape/structure
–Meshlike linked exoskeleton - peptidoglycan
- Maintains osmolarity: prevent osmotic lysis
- Survival: Cell wall interacts with host membranes
•Cell division: Forms cross-wall separating two daughter cells
bacterial cell wall synthesis
•Peptidoglycan precursor synthesised inside the cell
NAG/ NAM linked to lipid carrier- taken through cell membrane to new cell wall X bacitracin
intergrated into wall by enzymes (transpeptidase) create space then linked into existing structure
- The new nucleotide minus the terminal D-ala is encorporated
- Cell ‘grows’
cell wall morphology of mycobacterium
–Modified peptidoglycan layer
–Covalently attached to arabinogalactan polymer
–Mycolic acid waxy coat - lipids
–Poor Gram stain
–Acid fast (Zeihl-Neelsen stain) - carbolfuchsin
cell wall morphology of mycoplasma
–No cell wall
–Cell membrane contains steroids (host)
cell membrane features
- Lipid bilayer - hydrophobic
- Similar Gram +ve and –ve bacteria
- No steroids (except mycoplasmas)
- Ion transport and energy production (mitoch
- Mesosome - cell division
- Electron transport (energy production)
other (special) cell membrane features
•Spores
–Cell survival in adverse conditions
–Desiccation, heat, starvation
–Gram +ve only eg Bacillus spp./All Clostridium spp.
•Capsules
–Protection against phagocytosis
–Both Gram +ve / Gram –ve
–Gelatinous material, polysaccharide/polypeptide
•Flagella: chemotaxis, flagellin protein,
•Fimbriae (pili): pilin and adhesin
–E.coli (UTI)
–N.gonorrhoeae
–Sex pili (F plasmid)
Morphological virulence factors in gram negative
•LPS (LOS)
–Lipid A/core polysacc.
–Shedding – Meningos
–Inflammatory response
–Cytokines/Septic shock
- Porins
- Pili (N. gonorrhea)
Morphological virulence factors in gram positive
- Teichoic acids
- Lipoteichoic acids
- Peptido. Fragments
- Surface protein
–Afimbrial adhesins
–Protein F (Strep. pyogenes)
- Inflammatory response
- Cytokines/shock
growth characteristics: physical
–O2/CO2
–Temperature
–Water
–pH
–Light
–Osmolarity
Growth characteristics: nutritional requirements
–Carbon source
–Nitrogen source
–Inorganic salts (Fe/Na/K/P/Ca/Mg)
–Organic compounds (a-a’s?)
