Effects of enrofloxacin on the human intestinal microbiota in vitro.

An anaerobic, continuous-flow culture method has been developed to assess the effects of different levels of enrofloxacin (ENR) on the human intestinal microbiota. Chemostats containing human faecal flora were exposed to 1.25, 12.5 and 125 μg/mL ENR. Before and during drug exposure, samples aspirated from culture vessels were analysed using viable cell counting and denaturing gradient gel electrophoresis (DGGE). In addition, the colonisation resistance (CR) of the microbiota to Candida albicans SC5314 was evaluated. When exposed to 1.25 μg/mL ENR, total counts of aerobic bacteria, anaerobic bacteria, Lactobacillus, enterococci, Escherichia coli and Bacteroides fragilis were similar to the control group, except for Bifidobacterium; when exposed to 12.5 μg/mL and 125μg/mL ENR, numbers of categorised microorganisms changed significantly, except for B. fragilis. DGGE indicated that although 1.25 μg/mL ENR had little effect on the total number of microbiota, several bands representing dominant bacteria disappeared. The bands disappeared more quickly when exposed to 12.5 μg/mL and 125 μg/mL ENR. In addition to their influence on microbial diversity, different levels of ENR reduced the CR of the intestinal microbiota to C. albicans SC5314.