Monensin, Eimeria tenella infection, and effects on the bacterial populations in the ceca of gnotobiotic chickens.

Bacteria-free chicks in separate plastic film isolators were inoculated orally with single species of bacteria. Within an isolator, half the birds were fed unmedicated feed and half received feed containing 100 ppm monensin. With clostridium perfringens as the established species of monoflora, bacterial counts from the duodenum were 10(4) times lower and counts from the ceca were three times lower in monensin-fed birds compared to unmedicated birds. Infection with Eimeria tenella stimulated an eight-fold increase in the numbers of C. perfringens in the ceca of unmedicated birds but no increase in monensin-fed birds. With Bacteroides sp. or Streptococcus faecalis as monoflora, there was no difference in the cecal or duodenal populations between medicated and unmedicated birds uninfected with coccidia. In contrast to C. perfringens, populations of Bacteroides sp. and S. faecalis in the ceca decreased five to 100-fold in both medicated and unmedicated chicks after infection with E. tenella. Duodenal populations of C. perfringens, Bacteroides sp., and S. faecalis were unaffected by the coccidial infection.