Microbiology. Flashcards
3 main bacteria shapes.
Coccus-spherical
Bacillus-rod shaped
Spirillum-spiral/corkscrew.
Gram positive bacteria.
Violet or purple under microscope
Thick murein cell wall retains crystal violet
No lipopolysaccharide layer in cell wall.
Gram negative bacteria.
Pink or red from safranin under microscope
Thin peptidoglycan
Lipopolysaccharide layer
Salmonella, E.coli.
Lipopolysaccharide purpose.
Protection from attack by lysozyme and penicillin antibiotics.
Gram staining bacteria technique.
1) Smear glass slide with bacteria and fix with heat
2) Stain with crystal violet(binds to murein)
3) Treat with mordant lugol’s iodine to fix stain to peptidoglycan
4) Decolourise with alcohol to remove unbound crystal violet stain
5) Counter stain with safranin.
Things necessary to culture bacteria in a lab.
Carbon source, glucose
Nitrogen source
Growth factors- water, vitamins, minerals
Temperature
pH
Oxygen.
Obligate aerobes.
Can only reproduce or metabolise in an oxygen rich environment.
Facultative anaerobes.
Thrive in oxygen rich environment but can also respire anaerobically.
Obligate anaerobes.
Unable to reproduce or metabolise when oxygen is present.
Aseptic technique purpose.
Prevent contamination by the microbes being handled
prevent contamination of the cultures by microbes from the environment.
Aseptic technique method.
1) Sterilise all apparatus, surface and media before use with disinfectant
2) Flame necks of cultures vessels before opening/closing
3) Use inoculating loop to transfer bacteria (sterilise in red Bunsen before and after use)
4) Only lift petri dish lid slightly and when necessary
5) Secure petri dish lid with strips of tape, labelled & dated
6) Do not place cap of culture bottle down on a work surface
7) Incubate at 25 degrees Celsius for 24-48 hours
8) Sterilise plates and equipment after use.
What is an autoclave?
Used in a lab to sterilise
Sealed container
Glass and metal heated to 121 degrees
In steam under pressure for 15 mins after required pressure reached.
Viable count meaning.
Living cells only.
Total count meaning.
Living and dead cells.
Serial dilutions use and process.
Used in order to count the microbes more reliably
Original sample is diluted to give 20-200 colonies grown from the original bacteria sample
Multiply the counted colonies by the dilution factor= number of bacteria in 1cm3 of original sample (is a viable count)
Only count if after incubation diluted samples are not clumped/are too many/too few
Plate on sterile agar plates.
