Serovar distribution and antimicrobial susceptibility of swineSalmonellaisolates from clinically ill pigs in diagnostic submissions from Indiana in the United States

Abstract

To determine serovar distribution and levels of antimicrobial susceptibility of Salmonella isolated from clinically ill pigs in diagnostic submissions. A total of 197 Salmonella isolates were obtained by the Indiana Animal Disease Diagnostic Laboratory from 2003 to 2005. Minimal inhibitory concentrations (MICs) were determined using the standard microbroth dilution method. The top four serovars identified were Salm. enterica serovar Typhimurium variant Copenhagen, Salm. Derby, Salm. Choleraesuis var. Kunzendorf and Salm. Typhimurium. All isolates were susceptible to the fluoroquinolones tested except that eight isolates were intermediate to difloxacin. The isolates showed a low prevalence of resistance to trimethoprim/sulphadiazine (Sxt), gentamicin (G), ceftiofur (Cf) and cephalothin (Cp) with low MIC(50) value of <or=0.5, 0.5, 1 and 4 microg ml(-1), respectively. They showed a high prevalence of resistance to tetracycline (T; 83.8%), and a moderate prevalence to ampicillin (55.8%), spectinomycin (42.6%), ticarcillin (41.6%) and florfenicol (41.1%). There were more isolates of Salm. Typhimurium, including var. Copenhagen and Salm. Agona, that possessed multiple antimicrobial resistance to amoxicillin/clavulanic acid, ampicillin, ceftiofur and cephalothin (AxApCfCp) than the other serovars. The swine Salmonella isolates were susceptible to the fluoroquinolones, Sxt, G, Cf and Cp, but resistant to T. These findings provided useful information regarding antimicrobial susceptibility and resistance in dealing with clinical salmonellosis in pig herds.