Influence of chlortetracycline feeding on salmonellosis in calves. I. Rate and duration of shedding. II. Severity of illness.

Studies were conducted to test the influence of the feeding of chlortetracycline (CTC) on the fecal shedding of S. typhimurium subsequent to experimentally induced infection in calves. Levels of 0, 20, 50, and 100 gm CTC per ton of feed were fed to groups of calves for a two-week period before inoculation and the resulting level of shedding of S. typhimurium quantified. At the 50 gm/ton level, the feeding of CTC was associated with a significantly higher level of shedding than in non-CTC fed controls, and the duration of shedding was longer. Calves fed at 50 and 100 gm CTC/ton were affected much more severely by the inoculation than calves receiving no CTC. The same was true to a lesser extent in the calves fed 20 gm/ton. Observations made on each calf included changes in body temperature, time of onset, severity and duration of diarrhea, straining, and anorexia. Since the fecal output of salmonellae is increased at the level of 50 gm/ton, the authors conclude that this commonly used level of CTC feeding in calves contributes to the size of the salmonella reservoir in nature, thus increasing the risk of exposure to both man and animals alike and otherwise complicates the problems of salmonellosis.

Therapeutic responses of piglets to experimentally induced colibacillosis.

The purpose of these experiments was to determine the effects of prior exposure to antimicrobials on subsequent treatment of artificially induced colibacillosis in pigs. One- to two-week-old piglets were given 10(7) multiple antibiotic resistant Escherichia coli orally. Two groups of the piglets received priming doses at different levels of the antimicrobial preparation, ASP-250 before challenge. The remaining group received no antimicrobial. Piglets ill as a result of the challenge were treated with chloramphenicol of chlortetracycline, or received no treatment. Chloramphenicol was significantly more effective than chlortetracycline in terminating colibacillosis in the primed and unprimed groups. There were fewer deaths and relapse cases in those groups which received chloramphenicol treatment. Results in piglets treated with chlortetracycline were not significantly better than those which received no treatment.

Effect of a high-beef diet on the fecal bacterial flora of humans.

Ten human volunteers completed a 4-month diet series consisting of 1 month each of a control diet, a meatless diet, a high-beef diet, and the same control diet. Fat and fiber contents were essentially the same in all four diets, but protein content was doubled during the high-beef diet. During the 4th week on each diet, three stool specimens collected from each volunteer were analyzed for chemical composition and content of facultative, aerobic, and anaerobic bacteria. The bacteriological data are presented in this paper. High beef protein consumption had little effect on the composition of the intestinal flora. There were no significant differences in total counts of facultative and aerobic or anaerobic organisms in the feces when volunteers were on meatless or high-beef diets. At the species level, when counts during the two control diets were comparable, in only three instances did the change from the meatless to a high-beef diet significantly influence the bacterial numbers. The ratio of mean counts of anaerobic to facultative and aerobic organisms was approximately 15:1 during the meatless diet and 34:1 during the high-meat diet. The data indicate that animal protein consumption has little effect on the fecal bacterial profile in humans.

Effect of oral tetracycline on the occurrence of tetracycline-resistant strains of Escherichia coli in the intestinal tract of humans.

Serial samples of feces from normal human subjects were analyzed for tetracycline-resistant strains of Escherichia coli. Subjects were found to be excreting tetracycline-resistant strains in amounts fluctuating with time. Ingestion of tetracycline increased both the number of individuals excreting tetracycline-resistant strains of E. coli and the proportion of the total E. coli isolates resistant to the antibiotic.