Microbiology Differential Tests
Starch Agar
Purpose: Differentiate organisms based on their ability to hydrolyze starch via α-amylase and oligo-1,6-glucosidase
Gardnerella vaginalis, Corynebacterium, Clostridium, Bacillus, Bacteroides, Fusobacterium, Enterococcus
Ingredients: beef extract, soluble starch, and agar
Indicator: iodine
Urea Agar
Purpose: Differentiate organisms based on their ability to hydrolyze urea to ammonia and carbon dioxide with urease
Proteus, Morganella, Providencia
Ingredients: urea, yeast extract, potassium phosphate (monobasic & dibasic)
pH Indicator: phenol red
Phenol Red Broths
Purpose: Differentiate organisms based on their ability to ferment sugars via glycolysis
Enterobacteriaceae
Ingredients: peptone, carbohydrate (glucose, lactose, or sucrose)
pH indicator: phenol red
Methyl Red & Voges-Proskauer Test
Purpose
MR: Differentiate organisms based on their ability to produce stable acids via mixed acid fermentation
VP: Differentiate organisms based on their ability to ferment glucose but quickly convert their acid products to acetonin and 2,3-butanediol
Enterobacteriaceae
Ingredients: peptone, glucose, phosphate buffer
Indicators: methyl red, VP reagents A & B
Citrate Test
Purpose: Differentiate organisms based on their ability to use citrate as its sole source of carbon via citrate-permease
Enterobacteriaceae
Ingredients: ammonium dihydrogen phosphate, dipotassium phosphate, sodium citrate, magnesium sulfate
Indicator: bromthymol blue
Nutrient Gelatin
Purpose: Differentiate organisms based on their ability to hydrolyzing gelatin--derived from collagen--for metabolic purposes via gelatinases
Staphylococcus aureus, S. epidermidis, Serratia, Proteus, Bacillus anthracis, B. cereus, Clostridium tetani, & C. perfringens
Ingredients: gelatin, peptone, beef extract
Indicator: liquified medium
Sulfur-Indole-Motility (SIM) Medium
Purpose
S: Differentiate organisms based on their ability to reduce sulfur via cysteine desulfurase or thiosulfate reductase
I: Differentiate organisms based on their ability to produce indole via trytophanase
M: Differentiate organisms based on motility
Enterobacteriaceae, Salmonella, Francisella, Proteus, Morganella morganii, Providencia rettgeri
Ingredients: casein, animal tissue, ferrous ammonium sulfate, sodium thiosulfate
Indicator: Kovacs' reagent
(B) Staphylococcus aureus: Non-motile, hydrogen sulfide (-), indole (-)
(C) Salmonella arizonae: Motile, hydrogen sulfide (+)**, indole (-)
(D) Enterobacter aerogenes: Motile, hydrogen sulfide (-), indole (-)
(E) Proteus vulgaris: Motile, hydrogen sulfide(+), indole (+)
