Effects of Six Antimicrobial Drugs on Rat Intestinal Flora: Is the Rat Model of Predictive Value in Clinical Practice?

Impact of residual and therapeutic doses of ciprofloxacin in the human-flora-associated mice model

A study was conducted to evaluate the effects of therapeutic and residual doses of ciprofloxacin on the human intestinal flora implanted into germ-free mice. Ciprofloxacin was administered daily via drinking water at concentrations to provide doses of 0, 0.125, 1.25, and 12.5mg/kg b.w. Changes in the intestinal flora composition, alteration in bacterial enzyme activities, fecal short chain fatty acid concentration and bacterial cellular fatty acid profiles, overgrowth of resistant bacteria, and disruption of the colonization barrier were the endpoints evaluated in the feces of human-flora-associated (HFA) mice. Ciprofloxacin at all tested doses decreased significantly the aerobic populations and particularly the population of Enterobacteriaceae. Selection of resistant Bacteroides fragilis group was noticed in HFA mice receiving 12.5mg/kg b.w. In mice challenged with a Salmonella strain, exogenous Salmonella persisted in the feces of all treated mice indicating that the flora responsible for the colonization barrier effect was disturbed by the antibiotic treatment. None of the studied metabolic parameters of the flora were affected by ciprofloxacin at any dose level. Under the experimental conditions of the study, the no-observed-effect level of ciprofloxacin was found to be less than 0.125 mg/kg b.w.

Effects of daily oral administration of rifaximin and neomycin on faecal aerobic flora in rats

The aim of this study was to compare the influence of rifaximin and neomycin on faecal flora in rats. The study was performed on 18 Wistar rats (three groups of six male animals). Group 1 received rifaximin (50 mg kg(-1)/day), group 2, neomycin (50 mg kg(-1)/day) and group 3 was used as control. Drugs were administered orally, once daily for 3 days. Faecal specimens, collected from each rat on day 3, were cultured for the quantitative and qualitative determination of aerobic microorganisms. Rifaximin treatment produced a marked reduction in the number of total aerobic bacteria and Salmonellae; neomycin caused reduction in Salmonellae, but did not cause statistically significant changes in total aerobic bacterial count. The binding of neomycin with faeces could explain this limited activity, which does not correlate with the in vitro susceptibility of the organism affected. These results confirm that rifaximin is suitable for topical treatment to reduce selected bacterial load in the gut intestines.