Differential Reactions in the Colon Group of Bacteria

Abstract

A technique is described for detecting the production of acetyl-methyl-carbinol (V.-P. reaction) in 6 hr. cultures. The test reagent consisted of 0.3% creatine dissolved in 40% KOH. This creatine-KOH solution was employed satisfactorily for 3 weeks when stored at room temp. and for 6 weeks when stored at ice-box temp. A medium containing proteose peptone (Difco), and ferric citrate as an indicator was found to be particularly satisfactory for the detection of H2S production, and this phenomenon served to differentiate the strains which were V. P. negative, methyl red positive and citrate positive (genus Citrobacter) from the other members of the colon-aerogenes group. With an air temp. of 45-46[degree]C, employing the standard lactose broth medium, all (31) strains of Escherichia observed produced gas; all (54) Citrobacter strains failed to produce gas; and of 181 cultures of Aerobacter, 3.9% produced gas. At 45.5-46[degree]C, in the medium proper, marked inhibition of Escherichia was noted (only 38.7% producing gas) and in no instance was gas produced by any of the Citrobacter (54) or Aerobacter (181) strains examined. A medium containing boric acid is described which may be useful for detection of the genus Escherichia and to exclude the genera Citrobacter and Aerobacter. With this medium 97.3% of 150 strains of Escherichia showed gas whereas only 6% of 181 strains of Aerobacter produced gas in 48 hrs. at 37[degree]C. Gas was not produced by any of 57 strains of the genus Citrobacter tested.