Lactose Degraded Colon-Aerogenes Organisms in Normal Feces

The type of degradation of lactose-fermentation here considered is that in which bacterial growth in lactose broth produces no fermentation the first few days of incubation. After 2 to 14 days, acidity and gas production may appear. In other strains it is only after repeated subculture on lactose that this sugar is fermented. As a result of lactose-fermenting deficiency, degraded organisms are entirely missed in water analysis. Since dextrose fermentation is normal, degraded strains grow on Endo and Russell's medium like paratyphoids and complicate the examination of suspect material for members of the Salmonella group. Many, but not all, strains ferment saccharose promptly. This led Krumwiede 1 to add saccharose to Russell's medium to exclude these degraded forms designated in Park and Williams as “paratyphoid-like intermediates”. Kennedy et al. 2 have presented data for 22 strains of colon bacilli showing delayed lactose fermentation, in urine, stools and water.

We have been interested in the Escherichia-Citrobacter-Aerobacter ratio in saline suspensions of feces, fresh and after storage at 37° and icebox temperature. Lactose degraded organisms have been encountered. The fecal suspensions were first plated on Endo from which representatives of all colony types were fished to dextrose broth. From these tubes plates were again made on Endo and a well isolated colony picked to lactose broth. From this growth a third Endo plate was made from which again a well isolated colony was fished to lactose. By such technique we were reasonably assured of pure cultures and were able to exclude growth which failed to ferment dextrose. The strains isolated were tested for their gelatin liquefaction, action on litmus milk, growth on Simmons'citrate agar, production of indole and hydrogen sulfide, their methyl red and Voges-Proskauer reactions and for fermentation of saccharose, dulcite, cellobiose, α-methyl-d-glucoside and Levine's boric acid lactose broth.