Identification of antimicrobial resistance in Salmonella enterica isolates from swine slaughterhouses in the Philippines through different antimicrobial susceptibility test protocols

Abstract

The spread of antimicrobial resistance (AMR) is an impending crisis highlighted by the emergence of multidrug-resistant (MDR) pathogenic foodborne bacteria, such as MDR Salmonella enterica, due to the misuse and overuse of antibiotics in agricultural and livestock industries. Hence, quick, and accurate identification of AMR and resistance genes are of utmost importance to treat infections, monitor or safeguard food production, and trace the sources of AMR outbreaks. Conventional methods of antimicrobial susceptibility testing (AST) such as disk diffusion assays are relatively inexpensive but are labor-intensive, slow, and limited to phenotypic detection. Conversely, modern AST methods include polymerase chain reaction (PCR) and DNA sequencing, which are faster and provide more accurate genotypic detection. This study sought to detect resistance genes in S. enterica isolated from swine from Philippine slaughterhouses through various protocols of conventional and modern AST methods. Resistance to five antibiotic classes was examined. It was found that 50% (14/28) of the isolates were MDR, and resistance to tetracycline was found in all isolates. The most common genes detected from the isolates were tet(A) (39.3%), followed by tet(C) (28.6%), and tet(E) (25%). Also, 25% (7/28) and 25% (7/28) of isolates were resistant to one and two antibiotic classes, respectively. PCR methods were used only for detection of tetracycline resistance genes, as a model for molecular investigation. The results of this study demonstrated the growing prevalence of MDR in the agricultural industry and the necessity for improvement of its detection.