Phenotypic and PCR-based analysis of antimicrobial resistance in heat-treated multidrug-resistant Salmonella spp. and Campylobacter jejuni isolated from raw chicken meat.

Thermal processing is widely applied to control foodborne pathogens; however, methodological approaches for evaluating its impact on antimicrobial resistance (AMR) remain limited. This study establishes an integrated framework combining phenotypic susceptibility testing and PCR-based detection to assess heat-induced changes in multidrug-resistant (MDR) Salmonella spp. and Campylobacter jejuni isolated from raw chicken meat. Isolates were subjected to controlled thermal treatments (55°C and 60°C) for defined exposure intervals. Phenotypic antimicrobial resistance was evaluated using the standardized Kirby-Bauer disk diffusion method, whereas selected antimicrobial resistance determinants (blaTEM, tet(B), sul2, C257T mutation in the gyrA gene, tet(O), and blaOXA-61) were detected by conventional PCR using validated primer sets and appropriate positive and negative control strains. The methodological comparison revealed that exposure to 60°C significantly reduced phenotypic resistance across multiple antimicrobial classes, whereas 55°C produced minimal effects. In contrast, PCR assays consistently detected antimicrobial resistance gene (ARG) targets across all treatment conditions, including in samples lacking culturable cells. This divergence highlights differences between culture-dependent and PCR-based approaches for assessing antimicrobial resistance following thermal stress and demonstrates the sensitivity of PCR for detecting ARG targets after heat exposure. The proposed combined phenotypic-molecular workflow provides a reproducible approach for AMR assessment in processed food matrices and demonstrates that phenotypic susceptibility testing and PCR-based detection may provide complementary information when evaluating the effects of thermal treatments on MDR foodborne pathogens. This study contributes a practical methodological framework for evaluating AMR in thermally processed food matrices and highlights the value of integrating phenotypic and molecular approaches when assessing the effects of thermal treatments on MDR foodborne pathogens. However, conventional PCR detects only the presence of amplifiable DNA targets and does not provide information regarding DNA integrity, biological functionality, transcriptional activity, or horizontal transfer potential. Therefore, further studies employing complementary molecular and functional approaches are required to evaluate these characteristics following thermal processing.