Clonal spread of blaCTX-M-65 producing Salmonella enterica serovars detected in poultry retail meat in North Carolina, USA

Abstract

The rise of antimicrobial resistance (AMR) in Salmonella enterica poses a significant public health threat, particularly through the dissemination of extended-spectrum β-lactamase (ESBL) genes such as bla_CTX-M-65. This study investigated the prevalence, resistance profiles, and genomic characteristics of S. enterica isolates from retail poultry products in North Carolina, collected between 2020 and 2024. Among 132 isolates representing 25 serovars, 14 were identified as multidrug-resistant (MDR) strains harboring bla_CTX-M-65. Whole-genome sequencing revealed that these isolates belonged to three serovars-S. Infantis (n = 11), S. I -:r:1,5 (n = 2), and S. Senftenberg (n = 1)-with associated sequence types ST32 and ST14. Genomic analyses identified additional resistance determinants, including quinolone resistance-determining region (QRDR) mutations, and a range of mobile genetic elements, such as IncFIB(pN55391) plasmids. The genetic environment of bla_CTX-M-65 was conserved, with IS1380-bla_CTX-M-65-IS5 structures, highlighting its mobility potential. Phylogenetic analysis showed that isolates clustered by serovar, with strong associations to international lineages. These findings emphasize the ongoing clonal dissemination of bla_CTX-M-65 and MDR Salmonella in the food supply chain, necessitating enhanced surveillance and mitigation strategies to curb the spread of resistance genes in food production environments.

Keywords: Salmonella; ESBL; Food chain; Genomic surveillance; Horizontal dissemination.

Fig. 1

Representative genetic context of bla_CTX-M-65 of S. enterica serovars. Genes and shotgun sequences were extracted from the GenBank database. Arrows indicate the positions and directions of the genes.

Fig. 2

Maximum-likelihood phylogenetic tree of 53 S. enterica strains from different sources, countries, and years. The phylogeny is rooted at midpoint.