Abstract
The composition of intestinal microflora, the fecal concentration of short chain fatty acids (SCFA) and fecal pH were examined in a stallion which had been orally administered with antibiotics (Isoniazid and Rifampicin) for a long period under suspicion of Mycobacterium avium infection. The stallion had had frequent colic attacks and was poorly nourished. To clarify the effect of the administration of antibiotics, specimens of feces were obtained several times in each of three terms, namely antibiotics administration term, non-administration term and re-administration term, and these specimens were analyzed in the respects described above. In addition, to clarify the relationship between the clinical conditions and the composition of intestinal microflora, three healthy stallions (HSs) managed in the same environment were selected as a control group, and their feces were analyzed similarly. Moreover, to clarify whether or not antibiotic resistance had developed in intestinal bacteria against the administered antibiotics, the minimum growth inhibitory concentration (MIC) of each of the antibiotics was determined in individual strains of bacteria isolated from the sick and control stallions. None of the analyses revealed marked differences between the antibiotics non-administered term and the terms during which the antibiotics were administered. With respect to the antibiotics-sensitivity test, all strains isolated from the long-term antibiotics-administered stallion (LS) were found to have higher antibiotic resistance against isoniazid: Values of the MIC of isoniazid were more than 500μg/ml in all strains. Values of the MIC of rifampicin varied from strain to strain. They were not necessarily higher in strains isolated from the LS than those from the HSs. Fecal concentration of SCFAs were markedly higher and levels of fecal pH were significantly lower in the LS than those in the HSs. As for the composition of intestinal microflora, the proportions of Bacteroidaceae and Lactobacillus as well as total bacterial counts were higher in the LS than those in the HSs.The above results and findings at necropsy suggest that the differences between the LS and HSs in composition of intestinal microflora, fecal pH and fecal concentration of SCFAs did not directly result from the administration of antibiotics but resulted from functional disorders in the digestive tract in the LS.
