Prevalence of aadA1, aadA2, aadB, strA and strB genes and their associations with multidrug resistance phenotype in Salmonella Typhimurium isolated from poultry carcasses

This study aimed to assess the prevalence of aminoglycoside resistance genes in S. Typhimurium isolated from poultry carcasses in Iran, and to reveal the most prevalent patterns of antimicrobial resistance. A total number of 300 samples of poultry carcasses were analyzed. Salmonella was isolated from 245 samples (81.66%). Multiplex PCR showed that 56.3% of the samples belonged to serovar S. Typhimurium and the remainder (43.6%) contained the rest of serovars. The highest rate of drug resistance was observed for tetracycline (97.0%), nalidixic acid (87.0%) and amoxicillinclavulanic acid (67.4%). These serovars, however, were sensitive to cefotaxime (84.8%), sulfamethoxazole trimethoprim (77.6%) and gentamicin (71.0%). aadA1 gene was detected in 63 isolates (45.6%), aadA2 in 48 isolates (34.7%), aadB in 43 isolates (31.1%), strA in 52 isolates (37.6%) and strB in 31 isolates (22.4%). High prevalence of aminoglycoside resistance genes in S. Typhimurium was shown. Furthermore, there was a significant association (P < 0.02) between the presence of aadA1, aadA2, strA and strB genes and resistance to streptomycin. Also, there was a significant association (P < 0.001) between the presence of aadB gene and resistance to kanamycin and gentamicin.