FOOD 4150 Lab MEDIA & RESULTS

Plate Count Agar (PCA)

General-purpose agar with no selective agents; used for Standard Plate Count (SPC); colonies are white/tan and countable between 25–250 CFU.

3M Petrifilm Aerobic Count (AC)

Red colonies indicate viable aerobic bacteria; used for total aerobic plate count.

3M Petrifilm Rapid Yeast & Mold (RYM)

Yeast appear small with defined edges (pink/tan→blue-green) and molds appear large/fuzzy/blue-green; used to enumerate yeasts and molds.

3M Petrifilm E. coli/Coliform

Blue colonies with gas = E. coli (β-glucuronidase positive); red colonies with gas = coliforms; used as sanitation indicator.

MacConkey Agar

Selective for Gram-negatives (bile salts + crystal violet); differential for lactose fermentation; E. coli appears pink/brick-red with bile precipitate.

EMB Agar

Selective for Gram-negatives (eosin + methylene blue); differential for lactose fermentation; E. coli shows metallic green sheen.

Lauryl Sulfate Tryptose Broth (LST)

Selective for coliforms via lauryl sulfate inhibition of Gram-positive bacteria; lactose fermentation producing gas = presumptive coliform.

Brilliant Green Lactose Bile Broth (BGLB)

Selective for coliforms (brilliant green + bile salts); lactose fermentation producing gas = confirmed coliform.

EC Broth

Selective for fecal coliforms at 45°C; gas formation indicates fecal coliforms (typically E. coli).

KF Streptococcus Agar

Selective for Enterococcus spp. (sodium azide inhibits Gram-negatives); differential via TTC reduction; deep red colonies = E. faecalis

BHI Broth (Enterococcus Confirmation)

Used to assess thermotolerance at 46°C and growth in 6.5% NaCl; Enterococcus is Gram-positive

MYP Agar (Mannitol Egg Yolk Polymyxin)

Selective for Bacillus cereus (polymyxin B); differential via mannitol (pink background) and lecithinase halo (white precipitate).

Triple Sugar Iron Agar (TSI)

Differential for glucose/lactose/sucrose fermentation and H₂S; Salmonella shows red slant/yellow butt with possible black precipitate.

Lysine Iron Agar (LIA)

Tests lysine decarboxylation and H₂S; Salmonella gives purple slant/purple butt and may produce black precipitate.

Tryptone Broth (Indole Test)

IMViC test; Kovac’s reagent added; red ring indicates indole production (E. coli positive).

MR-VP Broth (Methyl Red)

Red color after methyl red addition indicates strong acid fermentation of glucose (E. coli positive).

MR-VP Broth (Voges-Proskauer)

Reagents A (α-naphthol) and B (KOH) added; pink color indicates acetoin production (VP positive).

Koser’s Citrate Broth

Tests citrate utilization; turbidity indicates positive result; E. coli is citrate negative.

Staph Express Petrifilm

Red-violet colonies indicate suspect Staphylococcus aureus.

Staph Express Disk

Contains toluidine blue O + DNA; DNase-positive organisms create pink zones confirming S. aureus.

Nutrient Broth (Pre-enrichment)

Used for non-selective pre-enrichment of Salmonella to resuscitate stressed or injured cells.

RVS Broth

Selective enrichment for Salmonella (magnesium chloride + malachite green) incubated at 42°C.

Tetrathionate Broth

Selective enrichment for Salmonella (tetrathionate + iodine + bile salts).

Salmonella Latex Agglutination Test

Serological confirmation test; visible clumping within 1–2 minutes = Salmonella positive.

3M Petrifilm Staph Express (Complete)

Red-violet colonies initially; Express Disk added for DNase-based pink confirmation zones.