Food Microbiology Lab Practical.pdf 2026//2027!!
Food Microbiology Lab Practical
Study online at https://quizlet.com/_4nsayr
1. Liquid Medium 0% agar
broths, infusions
used for growing large numbers of bacteria & biochemical testing
2. Semisolid media 0.4% agar
used to determine motility
promotes anaerobic growth
3. Solid media >1.5% agar
used to observe colonies, pure culture isolation, storage, biochemical tests
4. Complex media usually has unknown attributes
usually beef extract, yeast extract, or peptic digests of proteins
used when exact needs of microbe is unknown
used commonly for heterotrophs
5. Chemically de- used to culture autotrophs
fined (minimal) known amounts of pure chemicals
media
6. Selective media allows certain kinds of microbes to grow while inhibiting growth of others
provides only specific carbon sources
selective inhibition with dyes, salt, antibiotics
examples: mannitol salt agar, bile esculin agar
7. Differential me- used to differentiate between closely related microbes or groups of microbes
dia certain dyes or chemicals shows characteristic changes or growth patterns in
microbes used for identification
examples: Eosin methylene blue agar, MacConkey's agar, Blood agar, bile esculin
agar
8. Enriched media
Page 1 of 14 9/15/2026, 7:27:11 AM
, Food Microbiology Lab Practical.pdf 2026//2027!!
Food Microbiology Lab Practical
Study online at https://quizlet.com/_4nsayr
contains growth promoting nutrients, support a wide variety of microorganisms as
well as fastidious ones
examples: blood agar, Mueller hinton agar
9. Gram staining peptidoglycan layer is 20x thicker in gram positive cells, which allows them to retain
the crystal violet dye
problems with gram stains:
over decolorize - gram positive looks like gram negative
under color - gram negative looks like gram positive
gram variable - within a species due to old culture
10. Structure of O-polysaccharide repeat (40 units) -> core polysaccharide -> glucosamine phos-
lipopolysaccha- phate dimer -> fatty acids
ride
11. Decolorizer 95% ethanol + acetone
(gram stain) in gram positive cells, ethanol shrinks pores and increases dye retention, removes
excess stain
in gram negative cells, ethanol increases porosity by removing lipids from cell
envelope
12. Food sampling small sample is used to test large batch of food
aim for ~100g for each sample unit
Steps:
-weigh out food sample
-mix with fluid to homogenize (1:10 ratio)
-homogenize food sample
-plate sample for bacterial counts
13. Fluid for homog- suspension only:
enizing (food -sterile water, sterile saline, or PBS (phosphate buffered saline) is used
samples) growth & suspension:
-buffered peptone water
Page 2 of 14 9/15/2026, 7:27:11 AM
Food Microbiology Lab Practical
Study online at https://quizlet.com/_4nsayr
1. Liquid Medium 0% agar
broths, infusions
used for growing large numbers of bacteria & biochemical testing
2. Semisolid media 0.4% agar
used to determine motility
promotes anaerobic growth
3. Solid media >1.5% agar
used to observe colonies, pure culture isolation, storage, biochemical tests
4. Complex media usually has unknown attributes
usually beef extract, yeast extract, or peptic digests of proteins
used when exact needs of microbe is unknown
used commonly for heterotrophs
5. Chemically de- used to culture autotrophs
fined (minimal) known amounts of pure chemicals
media
6. Selective media allows certain kinds of microbes to grow while inhibiting growth of others
provides only specific carbon sources
selective inhibition with dyes, salt, antibiotics
examples: mannitol salt agar, bile esculin agar
7. Differential me- used to differentiate between closely related microbes or groups of microbes
dia certain dyes or chemicals shows characteristic changes or growth patterns in
microbes used for identification
examples: Eosin methylene blue agar, MacConkey's agar, Blood agar, bile esculin
agar
8. Enriched media
Page 1 of 14 9/15/2026, 7:27:11 AM
, Food Microbiology Lab Practical.pdf 2026//2027!!
Food Microbiology Lab Practical
Study online at https://quizlet.com/_4nsayr
contains growth promoting nutrients, support a wide variety of microorganisms as
well as fastidious ones
examples: blood agar, Mueller hinton agar
9. Gram staining peptidoglycan layer is 20x thicker in gram positive cells, which allows them to retain
the crystal violet dye
problems with gram stains:
over decolorize - gram positive looks like gram negative
under color - gram negative looks like gram positive
gram variable - within a species due to old culture
10. Structure of O-polysaccharide repeat (40 units) -> core polysaccharide -> glucosamine phos-
lipopolysaccha- phate dimer -> fatty acids
ride
11. Decolorizer 95% ethanol + acetone
(gram stain) in gram positive cells, ethanol shrinks pores and increases dye retention, removes
excess stain
in gram negative cells, ethanol increases porosity by removing lipids from cell
envelope
12. Food sampling small sample is used to test large batch of food
aim for ~100g for each sample unit
Steps:
-weigh out food sample
-mix with fluid to homogenize (1:10 ratio)
-homogenize food sample
-plate sample for bacterial counts
13. Fluid for homog- suspension only:
enizing (food -sterile water, sterile saline, or PBS (phosphate buffered saline) is used
samples) growth & suspension:
-buffered peptone water
Page 2 of 14 9/15/2026, 7:27:11 AM
