Antimicrobial drug susceptibility and treatment efficacy in mice against Escherichia coli and Salmonella spp isolated from feces of diarrheal animals

가축의 설사변에서 분리한 대장균과 살모넬라균의 항균물질 감수성과 마우스에서의 치료효과

Survey on MIC of antimicrobial drugs and its treatment efficacy in mice were conducted for the strains of Escherichia coli and Salmonella spp isolated from feces of young domestic animals with diarrhea in 1996. A total of 338 strains of E coli and 61 strains of Salmonella spp were examined for the susceptibility to 20 antibiotics and 7 synthetic antimicrobial drugs. The results indicated that the majority of strains were susceptible to amikacin(93.5%), cefoperazone/sulbactam(93.5%), cefotaxim(93.3%), cefomandole(92.8%), cefoperazone(91.6%) and ciprofloxacin(85.1%), in order. Although gentamicin, ciprofloxacin and norfloxacin showed the relatively low MIC distributions, erythromycin, doxycycline, sulfamethoxazole and oxytetracycline revealed the high MIC distributions to most of isolates. The $MIC_{90}$ of antimicrobials for E coli were > $62.5{\mu}g/ml$ in gentamicin, $2.0{\mu}g/ml$ in ciprofloxacin, $1.0{\mu}g/ml$ in norfloxacin, > $500{\mu}g/ml$ in erythromycin, $125{\mu}g/ml$ in doxycycline, > $1000{\mu}g/ml$ in sulfamethoxazole and > $250{\mu}/ml$ in oxytetracycline. In general, the MIC of E coli isolates was higher than that of Salmonella spp isolates. Although variation in synergism or additivity of antibiotic combinations were demonstrated, ampicillin-gentamicin was the most efficacious combination both against E coli and Salmonella spp with the fluctuation of 7.7-77.5%. In the experiment of treatment efficacy in mice, the highest survival ratio(83.3%) after challenge with pathogenic E coli and Salmonella typhimurium was detected in the group treated with gentamicin.