Effect of in-feed paromomycin supplementation on antimicrobial resistance of enteric bacteria in turkeys.

Histomoniasis in turkeys can be prevented by administering paromomycin sulfate, an aminoglycoside antimicrobial agent, in feed. The aim of this study was to evaluate the impact of in-feed paromomycin sulfate supplementation on the antimicrobial resistance of intestinal bacteria in turkeys. Twelve flocks of breeder turkeys were administered 100 ppm paromomycin sulfate from hatching to day 120; 12 flocks not supplemented with paromomycin were used as controls. Faecal samples were collected monthly from days 0 to 180. The resistance of Escherichia coli, Enterococcus faecium and Staphylococcus aureus to paramomycin and other antimicrobial agents was compared in paromomycin supplemented (PS) and unsupplemented (PNS) flocks. E. coli from PS birds had a significantly higher frequency of resistance to paromomycin, neomycin and kanamycin until 1 month after the end of supplementation compared to PNS birds. Resistance to amoxicillin or trimethoprim-sulfamethoxazole was also more frequent in PS turkeys. Resistance was mainly due to the presence of aph genes, which could be transmitted by conjugation, sometimes with streptomycin, tetracycline, amoxicillin, trimethoprim or sulfonamide resistance genes. Resistance to kanamycin and streptomycin in E. faecium was significantly different in PS and PNS breeders on days 60 and 90. Significantly higher frequencies of resistance to paromomycin, kanamycin, neomycin and tobramycin were observed in S. aureus isolates from PS birds. Paromomycin supplementation resulted in resistance to aminoglycosides in bacteria of PS turkeys. Co-selection for resistance to other antimicrobial agents was observed in E. coli isolates.

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.