Identification of Bacteria
- Starts w/ knowledge of colony appearance on plates & growth requirements
- appearance of individual bacterial cells
- staining characteristics
Gram staining - what is it
-how does it work
- Gram staining differentiates bacteria by chem. & physical properties of their cell walls - detects peptidoglycan
- Gram positive retains crystal violet due to thick layer of peptioglycan
- Gram negative lose crystal violet (are stained with counter stain safranin [pink]) due to v. thin peptoglycan wall
*is first step in identifying bacteria
Gram staining - what is it
-how does it work
- Gram staining differentiates bacteria by chem. & physical properties of their cell walls - detects peptidoglycan
- Gram positive retains crystal violet due to thick layer of peptioglycan
- Gram negative lose crystal violet (are stained with counter stain safranin [pink]) due to v. thin peptoglycan wall
To get a good gram stain (3)
- Use young cultural bacteria - gram positive bacteria that is old can leach out crystal violet (gives false impressions as to what’s in sample)
- Very thin smear of cells
- If staining unknown bact., use controls
Unique features of prokaryotes
-They don’t have a nucleus
Components of Bacteria; Ribosomes
- site of protein synthesis
- composed of RNA and protein
- abundant in bacteria due to fact they are continuously producing proteins (many of their genes are inducible)
Components of Bacteria; Nucleoid
-Features of Bacterial DNA
- Is a region in the cell where the chromosome is (usually single chromosome)
- composed of DNA (usu. ds) in circular formation (although are cases where it’s linear)
- Does not have introns
Components of Bacteria; Plasmid
- extra chromosomal DNA free in cytoplasm which encodes genetic information - usu. provide bacteria w/ extra proteins and abilities (i.e. toxins, cell adhesion proteins & enzymes)
- Can share DNA plasmids amongst bacterial cells (via conjugation using pili)
Components of Bacteria; Nucleoid
-C+G content
- Is a region in the cell where the chromosome is (usually single chromosome)
- composed of DNA (usu. ds) in circular formation (although are cases where it’s linear)
- Does not have introns
-Chromosome: C+G content varies from 24% to 70% depending on genus and species
Components of Bacteria; Plasma Membrane
- Bilipid membrane, fluid mosaic structure w/ proteins embedded (transport)
- Retains cytoplasm
- semi-permeable
- Location of metabolic processes (ATP generation requires electrons flowing across membrane)
- contains receptor molecules that can assist w/ gene regulation w/in cell
Components of Bacteria; Cell Wall
- Chemically complex, rigid structure
- is what gives bacteria shape*
- protects it from osmotic lysis
- has a role in pathogenicity
- Is a site of action for antibiotics (i.e. penicillin - inhibits enzymes involved in cell wall synthesis)
-Most bacteria have one - not mycoplasmas
Cell wall - peptidoglycan subunit
- Sugar based molecule w/ a.a. linked to it
- contains unusual a.a. not found in proteins (have different structure)
- Is a major component of cell walls
- aka murein
- is a large polymer
Gram Positive vs Gram negative envelope - structure
- Gram positive = large peptidoglycan layer w/ lipteichoic & telchoic acid embedded w/in
- periplasmic space between layer and plasma membrane
- Gram negative: outer membrane (has lipopolysaccharides), thin layer of peptidoglycan w/in periplasmic space and has another plasma membrane
-Gram positive sensitive to penicillin and lysozyme (gram negative isn’t)
Cell wall - peptidoglycan subunit
- Sugar based molecule w/ a.a. linked to it
- contains unusual a.a. not found in proteins (have different structure)
- Is a major component of cell walls
- aka murein
- is a large polymer
- made of N-acetylglucosamine & N-acetylmuramic acid
Cell wall - Lipopolysaccharide
- found in gram negative bacteria. Has 3 import. regions:
1. O polysaccharide (outer portion): repeats of 4-5 sequences of sugars - may be branched
- antigenic, generates specific immune response
- highly specific, gives the serotype to bacterium
2. Core polysaccharide (R=rough)
3. Lipid A: endotoxin made of fatty acids and N-acetylglucosamine - is the toxic element of LPS
Components of Bacteria; Capsule
- only found in some bacteria
- Surrounds cell
- composed of polysaccharides and sometimes polypeptides
- seen by negative staining
- roles in pathogenicity and cell protection - may confer ability to survive longer in body and evade immune system
Components of Bacteria; Glycocalyx
- slimy outer layer produced by some bacteria
- is a TYPE OF CAPSULE formed by thin layer of tangled polysaccharide fibers - occurs on surface of cells growing in nature
- involved in adhesion, clumping and biofilm formation
Biofilms - what it is
-e.g.
- Bacteria may attach to surface, produce slime, divide and produce microcolonies w/in slime layer = biofilm
- becomes an enriched & protected enviro for themselves and other bacteria
e.g. dental plaque
Components of Bacteria; Pili or Fimbriae
-Sex pilus
- short, proteinaceous rod-like structures extending from cell wall of certain types
- enable specialised bacteria to bind to sites of infection so they are not flushed away
Pili: antigenically distinct from each other - bind to specific cell receptors on cell
-longer than fimbriae - only a few per cell
Sex pilus: used for transferring DNA between bacteria
Components of Bacteria; Flagellum
- composed of protein flagellin
- located in cell wall & membrane
- Organs of motility
- Require energy - driven by rotary engine at anchoring point in inner cell membrane (pumps protons)
- rotates 200-1000rpm
*allows bacteria to move through aqueous soln. - move away from toxic substances or towards good substances
4 types of flagella
- Monotrichous (1 tail at polar end)
- Lophotrichous (many tails at one end)
- Amphitrichous (Tails at both ends)
- Peritrichous flagella (tails all around - i.e. E. coli) - need synchronisation for unidirectional movement)
*flagella usually 5-10 x longer than cell
Components of Bacteria; Endospores
- what they are for
- what they are not
- how to kill them
- Produced in poor growth conditions - enables long term survival in enviro. until conditions become favourable again
- Can be killed by hot air, autoclaving, formaldehyde and ethylene oxide, but not by boiling
*ARE NOT A REPRODUCTIVE STRUCTURE
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Bacteria Structure & Function22
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Bacterial Metabolism & Growth18
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Disinfection, Sterilisation & Antibiotics46
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Symbionts and Pathogens25
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Bacterial Identification, growth, gene exchange & Isolation25
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Bacterial Pathogenesis and Transmission21
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Enterobacteriacaea18
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Purulent and bacteraemic infections23
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Toxaemic and Respiratory Tract Infections18
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Granulomatous and Reproductive Tract Infections20
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Spirochaetaceae19
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Mycoplasmas11
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Rickettsias & Chlamydias28
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Opportunistic Pathogen: Pseudomonas aeruginosa14
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Antimicrobial Resistance14
