Identification of Sal. Pullorum and Analysis of Antimicrobial Resistance

NL Kuan1*, C Tu1, JH Shein2

Animal Health Research Institute, Council of Agriculture, Executive Yuan1

Department of Veterinary Medicine, National Chung Hsing University2

Abstract

The etiological agent of pullorum disease is Salmonella enterica subsp. enterica serovar Gallinarum-Pullorum biovar Pullorum (Sal. Pullorum), which incurs significant economic losses in the poultry industry worldwide. Increasing use of antimicrobial agents for disease treatment or prevention may be responsible for the rising incidence of drug resistant strains. Drug use presumably selects for integrons (mobile DNA elements) which may contain one to several resistant gene cassettes; these are implicated in the spread of antibiotic resistance markers from one bacterial strain or species to another. In this study, 26 isolates of Sal. Pullorum were included, and 42.3% (11/26) of isolates carried class I integrons of various sizes: 721 bp, 1,000 bp, and 1,900 bp. These integrons contained gene cassettes encoding resistance to aminoglycosides (aadA1 and aadA2) and trimethoprim (dhfrA12 and dhfrA25). All of the 3dhfr-positive isolates were resistant to sulfamethoxazole/trimethoprim; the 10 aadA-positive isolates were increased in the minimum inhibitory concentration of streptomycin. The results indicated that types of resistant gene cassettes reflected the relevant resistances in Sal. Pullorum isolates.

Keywords: Sal. Pullorum, antimicrobial resistance, integron.