Microbiology Flashcards
Draw and label the structure of a prokaryotic cell
Flagellum Pilus Circular DNA Plasma Membrane 70s Ribosome Peptidoglycan Cell Wall Slime Capsule Plasmid
What is the function of the plasma membrane in a prokaryote?
- barrier between the environment and the cytoplasm
- controls entry and exit of substances into and out of the cell
What is the function of the peptidoglycan cell wall in a prokaryote?
- prevents osmotic lysis
- rigidity and cell structure
What is the function of the slime capsule in a prokaryote?
- protect against other cell attack
- prevents cell drying out
What is the function of pili in a prokaryote?
Transferring plasmids (genetic information) by conjugation
What is the function of the flagellum in a prokaryote?
For mobility
What is the function of the plasmid in a prokaryote?
- contains extra bacterial genes, e.g. bacterial resistance
- can be exchanged between bacteria during conjugation allowing spread of resistance
What are the 3 bacterial shapes?
- Bacillus (Rod)
- Coccus (sphere)
- Spirillum (Spiral)
What are prokaryotes?
- no membrane bound nucleus
- no membrane bound organelles
- small ribosomes (70s)
- cell wall made up of peptidoglycan
- small cells, 0.5-5um
- reproduce by binary fission
What is the structure of gram positive bacteria?
- cell wall has a thick layer of peptidoglycan and a plasma membrane
What happens to gram positive bacterium in the Gram stain?
- peptidoglycan holds onto crystal violet dye
- dye is not washed out by ethanol and therefore appears purple in the Gram stain
What is the structure of Gram negative bacterium?
- thick outer layer of lipopolysaccharides with a thin layer of peptidoglycan
- plasma membrane beneath
What happens to Gram negative bacterium in the Gram stain?
- crystal violet dye is removed when rinsed with ethanol (dissolves the stained lipopolysaccharide layer)
- peptidoglycan is stained with the counter-stain and therefore appears pink in the gram stain test
What antibiotics interfere with Gram positive bacterium?
- Penicillin
- prevents bonds interlinking peptidoglycan forming
- when the bacteria divide, the cell walls are weak and collapse
- water uptake by osmosis bursts the cell
What antibiotics interfere with Gram negative bacterium?
- Require antibiotics that interfere with the cell’s metabolism/protein synthesis
- e.g. vancomycin
- penicillin is not effective as the outer layer protects the peptidoglycan
Why are animal cells not damaged by penicillin?
Animal cells do not have a cell wall, not damaged by penicillin
Definition of a Gram Stain
A method of staining the cell walls of bacteria as an aid to their identification
What is the method for the Gram-stain test?
- create a flame-fixed emulsion of bacterial samples on a slide
- flood with crystal violet, leave for 1 min then rinse of excess with sterile distilled water
- Add lugol’s iodine solution, leave for 1 min then rinse
- Flood with decolouriser (ethanol) for 30 seconds until run-off is clear
- Counter-stain with Safranin, leave for 1 min then rinse
- Gently blot dry slide
- Observe slide under oil immersion on a microscope
Why do you add alcohol/ethanol?
Alcohol removes unbound stain and lipopolysaccharide layer
Conditions necessary for growth and bacteria: temperature
- 25-45’c as metabolism is regulated by enzymes.
- mamallian pathogens optimum is 37’c
Conditions necessary for growth and bacteria: pH
- pH 7.4
- slightly alkaline conditions
- fungi prefer neutral to acidic conditions
Conditions necessary for growth and bacteria: oxygen
- some require oxygen
- some require anaerobic conditions
Conditions necessary for growth and bacteria: nutrients
- need a carbon and energy source ususally glucose
- need nitrogen source in organic or inorganic form for amino acid synthesis
- need growth factors; minerals and vitamins
What is the aseptic technique when handling bottles and caps?
Hold bottle cap in little finger and flame the bottle neck beofre and after extracting bacteria
