Antibiotic Associated Diarrhea in Horses With special reference to Clostridium difficile

Gustafsson, A. 2004. Antibiotic associated diarrhea in horses, with special reference to Clostridium difficile. Doctor ́s dissertation. ISSN 1401-6257, ISBN 91-576-6652-0 Antibiotic associated diarrhea is a serious illness in horses with high mortality. Affected horses are often hospitalized, with the disease appearing after a few days of antibiotic treatment. Another risk group for developing this acute diarrhea appears to be healthy mares with foals under treatment with oral erythromycin and rifampicin for Rhodococcus equi pneumonia. In humans, C. difficile is the agent most often implicated in antibiotic associated diarrhea. When the present work was initiated this organism was not reported as a pathogen in adult horses. The aim of this thesis was to evaluate the impact of antibiotic treatment on the equine intestinal microflora with focus on the risk for development of antibiotic associated diarrhea and its connection to C. difficile. C. difficile and/or its cytotoxin was demonstrated in 40% of horses with acute colitis developing during antibiotic treatment but not found in other groups. All of these horses were treated with β-lactam antibiotics. The influence of different antibiotics was further evaluated in experimental studies. It was demonstrated that very low oral doses of erythromycin could induce acute colitis associated with C. difficile, thus, suggesting that the fatal colitis affecting the mares with foals under treatment for R. equi pneumonia was due to accidental ingestion of erythromycin. In contrast, very low oral doses of rifampicin and therapeutic doses of both oral and i.v. trimethoprim/sulfadiazine induced neither gastrointestinal disturbances nor major changes in the intestinal flora. In an oral infection model, C. difficile was cultured from faecal samples on significantly more sampling occasions from horses pre-treated with penicillin than from untreated horses indicating that penicillin treatment can predispose to establishment of C. difficile in the horse intestine. This work demonstrates that antibiotic treatment is one of the most important risk factors for development of acute colitis in the horse. Antibiotics known to be associated with a high risk for development of colitis, such as erythromycin should be avoided. However even pencillin poses a risk. As C. difficile is associated with acute colitis in adult horses being treated with antibiotics, routine examination for C. difficile is recommended in cases of antibiotic associated diarrhea.