Antimicrobial Susceptibility and Resistance Gene Determinants in Clinical Escherichia coli and Salmonella enferica serovar Choleraesuis Swine Isolates

Abstract

Escherichia coli and Salmonellae infection are very common in people and animals worldwide. The emergence of multidrug resistance in these bacteria is increasing significantly in both animal industry and human medicine. The aims of this study were to determine the antimicrobial susceptibility of the isolates to various antimicrobial agents and to identify some of the resistance genes. Sixty clinical isolates of each E. coli and Salmonella enterica serovar Choleraesuis collected during 1997 to 2001 from diseased pigs in Taiwan were evaluated for minimum inhibition concentration (MIC) value to antimicrobial agents. These isolates were analyzed for antibiotic resistance genes such as tem and florR by polymerase chain reaction (PCR). The correlation of virulence factor and integrons to antimicrobial resistance from the Salmonella isolates were also identified by PCR. The MIC values indicated that E. coli and Salmonella isolates had the highest activity in vitro to amikacin and ceftiofur whereas cephalothin, doxycycline, florfenicol, and gentamicin were moderately active. Flumequine was moderately active against isolates of S. enterica serovar Choleraesuis but was inactive against E. coli. Ampicillin, chloramphenicol, chlortetracycline, nalidixic acid, kanamycin, streptomycin, sulfamethoxazole, tetracycline, and trimethoprim were all inactive. The prevalence of integrons in E. coli and S. enterica serovar Choleraesuis were 97% and 95%, respectively. The prevalence of extended-spectrum β-Iactamase (tem) and florfenicol resistance (floR) in E. coli were 38% and 55%, respectively. The prevalence of tem, floR and spvC (Salmonella plasmid virulence C gene) in S. enterica serovar Choleraesuis were 60%, 25%, and 98%, respectively. The study indicated that multidrug resistance in swine E. coli and S. enterica serovar Choleraesuis isolates is predominant, and 95-97% of the isolates possess integron. A surveillance system was suggested to monitor the emergence of multidrug resistant in E. coli and S. enterica serovar Choleraesuis in swine industry.