Antibiotic resistance and resistance genes in Salmonella enterica isolated from pork meat and pig carcasses in Northern Italy.

Introduction- The selective pressure imposed by the widespread use of antimicrobial agents in veterinary medicine may have contributed to the dissemination of multidrug resistant bacterial strains. Moreover, an increase in antibiotic resistance has been reported recently in Salmonella spp. isolated from foods of animal origin. Notoriously, multi-drug resistance in S. enteric can be associated both with specific genes and non-specific resistance mechanisms. Aims- The objectives of this study were to assess the isolation frequency, to determine the serotype and to evaluate the antibiotic resistance of Salmonella spp. isolated from pork meat, pork meat preparations and pig carcasses. Above all S. Enterica isolates were screened to investigate the relationship between the antibiotic resistance towards ampicillin, gentamicin, sulfamethoxazole and tetracycline and the presence of the related genes blaPSE-1 , ant(2’’)-Ia, sul-1,tet(A), tet(B) and tet(G) and marRAB. Materials and methods- S. enteric isolated among 2004 and 2009 from pork meat, pork meat preparations and pig carcasses were analyzed using both phenotypic and molecular methods. Antibiotic susceptibility of the isolates was tested for ampicillin, gentamicin, sulfamethoxazole and tetracycline. Simplex and multiplex PCR protocols were used for detecting the presence of resistance genes. Results- The most frequently isolated serovars were S. Derby and S. Typhimurium. S. Rissen was isolated only from pig carcasses. Most Salmonella isolates were resistant to tetracycline; the antibiotic pattern Am, Sxt and Te was observed in the majority of isolates. Tet(A) and tet(B) genes were mainly detected in S. enterica isolated from pig carcasses. The presence of marRAB was higher in S. Enteric isolated from pork meat. Discussion- The correlation between the resistance phenotypes and the related genes was not always shown; this may be due to the limited selection of investigated genes or to non-specific resistance mechanisms. In our study there was no correlation between the presence of marRAB and resistance towards tetracycline. Conclusions- The high presence of Multi Drug Resistant S. enterica isolated from foodstuff represents a risk for public health, especially when microorganisms are resistant to antibiotics with different mechanisms of action. Moreover, the lack of correlation between the phenotypic resistance and the related selected genes suggests the presence of other specific or non-specific mechanisms involved in the antibiotic resistance phenomenon.