Differentiation of B. aerogenes and B. coli of non-fecal origin from B. coli of fecal origin.

Abstract

Koser 1 2 3 has demonstrated with the “colon bacilli” that B. aerogenes and B. coli isolated from soils utilize citrates as a source of carbon and that B. coli of fecal origin does not use it. One of us was interested in isolating iron precipitating bacteria. Harder's 4 medium which consisted of K₂HPO₄ 0.5 gm., MgSO₄ 0.5 gm., (NH₄)₂SO₄, 0.5 gm., CaCl₂, 0.2 gm., NaNO₃, 0.5 gm., Ferric Ammonium citrate 10 gm., H₂O, 1000 gm., Agar 18 gm., was used. The medium is pale yellow in color; when the iron precipitating bacteria grow on this they produce a vivid heavy iron rust streak. It is possible that these bacteria use the citrate and mechanically precipitate the red iron compound. It was thought of interest to try the “colon bacilli” on this medium and compare it with Koser's medium, which consists of NaCl, 5 gm., MgSo₄, 0.2 gm., (NH₄) H₂PO₄, 1 gm., K₂HPO₄, 1 gm., and sodium citrate 2 gm., in 1000 gm. H₂O.

Ninety-one strains of the “colon bacilli” were isolated from sewage, (and in addition a B. coli of fecal origin, a B. coli of non-fecal origin and a B. aerogenes kindly supplied by Dr. KOser) were used. These were streaked on the Harder medium and inoculated into Koser's medium. The Voges-Proskauer test was also carried out. The incubation was 2 to 5 clays at 37½° C. The following results were obtained :

45 (B. coli, Voges-Proskauer negative) did not darken the Harder medium nor produce turbidity in the Koser medium.

47 (B. aerogenes, Voges-Proskauer positive) darkened the Harder medium and produced turbidity in the Koser medium.

2 (B. coli, Voges-Proskauer negative, Intermediate) darkened the Harder medium and produced turbidity in the Koser medium.