Long-term antimicrobial resistance in Escherichia coli from human intestinal microbiota after administration of clindamycin.

The aim of this study was to gain better knowledge of how the intestinal microbiota are affected over time after administration of an antimicrobial agent. This study monitored the prevalence and frequencies of antibiotic resistance in Enterobacteriaceae against 17 antimicrobial agents, during a 2-y period, in consecutive faecal samples collected from 8 healthy volunteers. Four subjects had received 150 mg clindamycin perorally for 7 d, while 4 non-exposed subjects served as a control group. The samples from both groups were cultured and screened for Enterobacteriaceae. The highest incidence of resistance observed was to ampicillin. The ampicillin resistance is due to production of the beta-lactamase TEM-1. The administration of clindamycin had a prolonged impact on the composition of the microbiota, even though enterobacteria are intrinsically resistant to clindamycin; the level of resistance in Escherichia coli isolates was elevated after administration and persisted up to 9 months after administration. After 9 months the susceptibility levels in the exposed group were similar to those at d 0.