Phenotypic-genotypic resistance in Salmonella spp. isolated from cattle carcasses from the north central zone of the State of Mexico.

Salmonella is a public and animal health problem due to the generation of strains multiresistant to antimicrobial products. The objective of this study was to determine prevalence and antimicrobial phenotypic and genotypic resistance of Salmonella spp. isolated from beef cattle carcasses killed in slaughterhouses of the north central zone of the State of Mexico. Sampling was carried out according to the European Directive 2001/471/EC; isolation and identification of the strain was carried out according to the Mexican Official Standard NOM-114-SSA1-1994; resistance was established by CMI according to the National Committees for Clinical Laboratory Standards (NCLS) and multiplex PCR according to Ahmed et al. (Journal of Applied Microbiology 106:402-409, 2009) with PSE-1, tetG, qnrS, FloR, STR, and sul1 oligonucleotides. Twenty-seven strains of Salmonella spp. were obtained from 327 samples (prevalence of 0.083); 19 strains (70 %) were resistant to 10 μg/ml of ampicillin, 15 of these (79 %) had the PSE-1 gene; 22 strains (84 %) were resistant to 30 μg/ml streptomycin, 14 of these (63.6 %) had the STR gene. Genes PSE-1 and STR were factors in the presence of resistance, the rest of the genes (tetG, qnrS, FloR, and sul1) were not factors of resistance in the studied strains.