Microbiology SWA

Coccus (1), cocci (2+)
Spherical shaped

Bacillus (1), bacilli (2+)
Rod shaped

Spirillium
Spiral / corkscrew shaped

Gram negative (red), gram positive (purple)

• Smear bacteria sample onto glass slide
• Heat to fix sample
• Stain with crystal violet
• Put iodine on to fix stain
• Decolourise with alcohol to remove unbound stain
• Use counter stain Safranin

Only has thick pepticoglycan cell wall so retains crystal violet stain

Has lipopolysaccharide layer to protect thin pepticoglycan wall
Lipopolysaccharide layer doesnt retain crystal violet so washed away by alcohol
Stains red bc of Safranin

Protect thin pepticoglycan gram negative wall
Protects against lysozymes and penicillin
So more difficult to control

Number of alive and dead cells in sample

Number of alive cells only in sample

Viable count, only the living cells can divide to form a colony

inbetween 10-100 colonies

•1cm3 of water in tube
•0.1cm3 of sample
• Put in first tube and mix
• Take 0.1cm3 of first tube sample and repeat
• Repeat until you get to 10,000 dilution factor
• Count no. of colonies seen

Over 100- too many to count, colonies may merge together
Under 10- not enough to reliably estimate

Nutrients- Needs carbon source to grow (eg, glucose)
Optimum pH (7.4)
Optimum Temperature (25°-45°)
Oxygen for metabolism

Obligate anaerobe- needs no oxygen
Obligate aerobe- needs oxygen
Facultative anaerobe- can thrive in both, rathers oxygen

Prevent contamination of environment by sample
Prevent contamination of culture by microbes from environment

• Sterilise equipment b4 and after by heating it on bunsen burner on red flame
• Use inoculation loop to transfer bacteria
• Lift petri dish lid slightly when transfer prevent environment microorganisms contaminating
• Secure lid with tape
• Sterilise

Defined medium
Undefined medium
Selective
Complete

Only known ingredients in the culture

Not all of the ingredients are known

Only allows certain bacteria to grow

Contains all chemicals needed to grow