Distinguishing Enterobacteriaceae

Large family of bacteria
Gram negative rods
Capable of fermenting various sugars
Many found in the intestines of human or other mammals
Varrying pathogenicity:
Commensals, opportunists or pathogens
Some found in the environment
Example species:
Escherichia coli
Klebsiella pneumoniae
Citrobacter freundii
Enterobacter aerogenes
Proteus mirabilis
Salmonella typhi
Shigella dysenteriae
Yersinia enterocolitica
Large amounts of acid from lactose fermentation cause the dyes to precipitate on the colony surface, producing a black center or a “green metallic sheen” (E. coli)

Smaller amounts of acid production result in pink coloration of the growth (E. aerogenes)

Nonfermenting enterics do not produce acid so their colonies remain colorless or take on the color of the media (P. vulgaris)
Triple Sugar Iron (TSI): fermentation of sugars, sulfur reduction

IMViC:
Indole: Break down the amino acid Tryptophan
Methyl Red: Glucose oxidation
Voges-Proskauer: Production of neutral end products
Citrate: Citrate fermentation

Urease: Hydrolyzation of Urea

Phenylalanine Deaminase: converts the amino acid phenylalanine to phenylpyruvic acid

Nitrate Reductase: Reduction of nitrate (NO3) to nitrite (NO2)