Promotion of the translocation of enteric bacteria from the gastrointestinal tracts of mice by oral treatment with penicillin, clindamycin, or metronidazole.

Specific pathogen-free mice were treated orally with antibiotics to determine whether the resulting disruption of the normal flora ecology would allow certain gram-negative enteric bacteria to overpopulate the ceca, thereby promoting the translocation of these bacteria from the gastrointestinal tract. The mice were treated orally with penicillin, clindamycin, or metronidazole for 4 days, and then the antibiotic was discontinued. The mice were tested at various intervals for viable enteric bacilli translocating from the gastrointestinal tract to the mesenteric lymph nodes. Penicillin treatment decreased the total anaerobe population levels in the ceca an average of 1,000-fold, whereas clindamycin treatment decreased these anaerobe levels only 10-fold, and metronidazole treatment slightly increased the anaerobe levels. Penicillin or metronidazole treatment slightly increased the anaerobe levels. Penicillin or metronidazole treatment increased the enteric bacilli populations in the ceca an average of 1,000-fold, whereas clindamycin treatment increased the enteric bacilli populations 100,000-fold. The peak incidence of translocation of the enteric bacilli to the mesenteric lymph nodes averaged 100% after penicillin treatment, 97% after clindamycin treatment, and 62% after metronidazole treatment. Thus, oral treatment of mice with penicillin, clindamycin, or metronidazole for only 4 days disrupts the normal flora ecology, allowing an overgrowth in the ceca of the gram-negative enteric bacilli and promoting their translocation to the mesenteric lymph nodes.