Bacteria: Structure, Growth, Taxonomy

Understanding of the structure of a bacterial cell State the Structural differences between bacteria and Eukaryotes Taxonomy and diagnosis of bacteria Structure/function features of cell envelope Growth conditions for bacterial growth

what are bacteria?

unicellular microorganism (can be free living or host dependant).

What kingdom are bacteria in?

Monera- single cells

difference between Monera and protists?

Monera - prokaryotes, unpaired chromosomes, no nucelus
Protits - eukaryotes, paired chromosomes, nuclear structure.

table comparing Prok vs Euk

What structure do both prokaryotes an eukaryotes have?

Nucleic acid, ribosomes, cell membrane

What structures are in eukaryotes and not prokaryotes ?

Structured nucleus, mitochondria, ER/Golgi

typical bacterial cell structure

Coiled DNA, Ribosomes, pili, inner membrane, cell wall, outer membrane, flagellum in the inner membrane,

Which bacteria has outer memebrane

gram - negative

What is binomial nomenclature?

two word naming system.
Genus then species.

why is bacterial taxonomy important?

- Handling information
- Learning
- Communication
- Identification
- Evolution

methods of classification - phenotypic

morphology - macroscopic/ microscopic
bio typing - biochemical tests
serotyping - differences in antigenic determinants on the outside of the cell

macroscopic morphology (growth on agar medium)

-shape
- margin
- elevation
- size

macroscopic morphology

- texture (smooth/rough)
- appearance (glistening (shiny) or dull)
- pigmentation (none = cream, tan, white/ pigmented = purple, red, yellow)
- optical density (opaque/translucent)

microscopic morphology characteristics?

- shape (rod, club, coccus, etc.)
- size
- staining characteristics (gram stain 'truce bacteria'. acid-fast stain 'mycobacteria')
- arrangements (individual , clusters)

-Optical density

genotypic characteristics?

- %G+C ratios → Amount of bases
- PCR/DNA sequencing → Banding patterns
- ribotyping (classifying based on sequence of ribosomal RNA (16s RNA)

what does a gram stain do?

differentiated bacteria on basis of their cell wall structure.
Generally first line test in diagnosis of bacterial infections.

what does gram positive mean?

thick cell wall

what is gram negative?

thin cell wall

what is added to perform gram staining?

- crystal violet - stains all cells
- gram's iodine - Thickens the crystal violet in the cell wall
- decolouriser (alcohol/acetone) - if gram-positive then can’t remove the crystal violet
- safranin red only applies to gram-negative

examples of morphological characterisation

In terms of cell envelope characteristics. What are the difference between both gram + and - have?

+ = Thicker, teichoic acid on top, sporulation, sensitive to lysozyme, more susceptible to penicillin

- = thiner wall , LPS , less susceptible to penicillin

In terms of cell envelope characteristics. What does both gram + and - have?

capsules

what is the function of porins?

Within the Plasma Membrane, they are proteins that allow certain ions and small polar molecules to pass through the membrane.

functions of cell wall?

- rigidity and cell shape and structure
- maintains osmolarity
- survival
- cell division

how is the bacterial cell wall synthesised?

peptidoglycan precursor synthesised inside the cell.

→
exported across the cell membrane X bacitracin (prevents secretion of the precursor unit of the cell wall)

→
a site is created in the existing wall by enzymes (PBPs).

→
new nucleotide minus the terminal D-ala is incorporated.

→
cell grows.

Different cell wall morphologies - Mycobacterium

- modified peptidoglycan layer
- covalently attached to arabinogalactan
- mycolic acid waxy coat - lipids → causes cells to clump
- poor gram stain
- acid fast - carbolfuchsni.

mycoplasma

- Type of bacteria

-no cell wall
- cell membrane contains steroids (host)

what is the cell membrane like?

- lipid bilayer - hydrophobic
- similar gram +ve and -ve bacteria
- no steroids (except mycoplasmas)

role = ion transport and energy production
- mesosome - cell division
- electron transport (energy production)

What other morphological features : spores?

spores
- cell survival in adverse conditions
- desiccation, heat, starvation
- gram +ve only

what other morphological features like capsule

capsules
- protection against phagocytosis
- both gram +ve/-ve
- gelatinous material, polysaccharide/polypeptide

Flagella + Fimbriae

Flagella:
- cell motility
- coiled in structure
- anchored in bacterial membranes

Fimbriae:
- smaller length and diameter
- not coiled

Main role of flagella and fimbirae ?

flagella =–Chemotaxis , Movement by ATP-driven ‘motor’ membrane potential

fimbirae - Adhesin

morphological virulence factors (What can you find? ) - Gram-negative

LPS
- lipid A/core ploysacc
- shedding - meningos
- inflammatory response
- cytokines/septic shock
Porins
Pili

morphological virulence factors (What can you find? ) - gram positive

Teichoic acids - in the inner membrane
Lipoteichoic acids
Peptido fragments
surface protein
- afimbrial adhesins
- protein F
Inflammatory response
Cytokines/shock

physical growth characteristics

- oxygen/carbon dioxide
- temperature
- water
- pH
- light
- osmolarity

nutrition requirements growth characteristics

- carbon source
- nitrogen source
- inorganic salts (Fe/Na/K/P/Ca/Mg)
- organic compounds (ammino acids?)

Medical relevance?

cell wall synthesis - for antibiotic killing
capsules - vaccines
cell membranes - antibiotics (only negative )/ vaccines
ribosomes - antibiotics that target ribosomes like tetracyclines