Co-occurrence and genetic interplay of ESBL and non-ESBL resistance determinants in multidrug-resistant Salmonella from poultry and associated environments in Abakaliki, Ebonyi State, Southeastern, Nigeria: a one health approach

The escalation of antimicrobial resistance Salmonella species remains a major public health threat, especially in livestock farming. Evidence on the co-occurrence of Extended Spectrum beta – lactamase (ESBL) and non-ESBL resistance determinants in poultry-associated Salmonella under a One Health framework remains scarce. This study aims to evaluate the prevalence, phenotypic resistance, and genetic co-occurrence of extended spectrum beta lactamase and non-ESBL resistance determinants in multidrug-resistant Salmonella isolated from poultry products and environmental sources in Abakaliki, Ebonyi State, Nigeria. This cross-sectional study was conducted from January - December 2025. Two hundred samples were collected from farms and retail outlets. Salmonella was isolated and identified using standard methods. Antimicrobial susceptibility was determined by Kirby–Bauer disk diffusion following Clinical and Laboratory Standards Institute guidelines, while double-disk synergy testing verified ESBL expression. Polymerase chain reaction screened for ESBL genes ( blaTEM , blaSHV ) and non-ESBL markers ( tetA , qnr , sul1 ). Multiple antibiotic resistance index values, multidrug resistance, clustering, network analyses were evaluated at p < 0.05. Of 200 samples, 52 Salmonella isolates (26.0%), confirming contamination across poultry products and environmental reservoirs. Poultry meat had the highest proportion (34.6%) of isolates, followed by drinking water (19.2%). MARI values ranged from 0.31 to 0.74, indicating high antibiotic use pressure. Multidrug resistance was highest from poultry meat (83.3%). Phenotypic ESBL production was detected in 36.8% (14/38) of MDR strains. Molecular analysis showed high frequencies of sul1 (57.9%), tetA (63.2%), and blaTEM (63.2%), whereas qnr was absent. Co-occurrence and network models confirmed strong clustering between ESBL and non-ESBL targets, revealing recurrent blaTEM – tetA – sul1 multi-gene assembly circulating within the poultry production environment. These findings confirm widespread co-occurrence of ESBL and non-ESBL resistance determinants within multidrug-resistant Salmonella circulating in Abakaliki, Ebonyi State, Southeastern Nigerian poultry networks. With 73.1% [38/52] MDR and 36.8% [14/38] ESBL rates, this genetic intersection of blaTEM – tetA - sul1 suggests co-selection as a major driver of AMR persistence and spread. This highlights the need for One Health interventions involving antimicrobial stewardship, improved farm sanitation, diagnostic surveillance, routine co-occurrence profiling to guide targeted regional control strategies and strict farm biosecurity to mitigate regional public health risks. Not applicable