Spent hen slaughter lines as reservoirs of multidrug resistant Salmonella spp.

This study investigated the prevalence of Salmonella spp. and their antimicrobial resistance in a high-capacity poultry slaughterhouse processing spent laying hens, which are considered a high-risk group in terms of food safety due to their extended production cycle and increased exposure to environmental pathogens associated with their longer lifespan. In total, 204 environmental and carcass samples were collected from 17 critical processing points during morning and evening operations across two visits. Salmonella spp. isolation followed the USDA/FSIS protocol, with confirmation by PCR targeting the invA gene. Multiplex PCR was employed to identify S. Enteritidis, S. Typhimurium, and S. Infantis. Antimicrobial susceptibility was evaluated using the disk diffusion method against 12 antibiotics spanning β-lactams, aminoglycosides, fluoroquinolones, carbapenems, and folate-pathway inhibitors, with interpretations based on EUCAST (2023) guidelines. Overall, 29 isolates (14.21%) were confirmed as Salmonella spp. The highest recovery occurred on the electroshock surface and packaging bench (33.3%), followed by live line hangers, knives, and personnel hands (25.0%). Moderate contamination was detected on transfer belts, evisceration equipment, cooling water, and final products (16.7%), whereas scalding tank surfaces and evisceration benches exhibited the lowest prevalence (8.3%). Three isolates from live hangers, scalding tank surfaces, and packaging counters were resistant to all tested antibiotics. Cefuroxime resistance was most common, followed by Ampicillin and Amoxicillin/Clavulanic acid, while only two isolates displayed resistance to Imipenem. Multidrug resistance was identified at five processing points, including final products. These results underscore the role of spent hen slaughter lines as potential reservoirs of multidrug-resistant Salmonella spp., reinforcing the need for strengthened hygiene and targeted control strategies.