Microorganisms in the Intestines of Rats Fed Penicillin

Abstract

Rats were fed penicillin G sodium in a complete synthetic ration or in one low in thiamine, and the numbers of organisms in different parts of the intestinal tract were determined at intervals. Penicillin caused decreases in the concentration of anaerobes in the cecum and in both upper and lower small intestine during the first week of the experiment, and more persistent increases in the numbers of coliforms. The numbers of enterococci or lactobacilli were not altered by the levels of penicillin fed. The level of thiamine in the diet did not appear to affect the numbers of the various types of organisms studied.