Molecular characterization of Salmonella isolates from poultry in Egypt: Detection of virulence, ESBLs genes and antimicrobial resistance profiling.

Abstract

This study aimed to determine the prevalence, serovars, virulence gene profiles, antimicrobial resistance patterns, and extended-spectrum β-lactamase (ESBL) genes in Salmonella isolated from broiler chickens in Egypt. In this study, 200 samples were obtained from broiler chickens. Samples were processed using standard bacteriological techniques, and suspected isolates were biochemically identified and molecularly confirmed by PCR targeting the invA gene. Serotyping was performed according to the Kauffmann-White scheme. Virulence genes (hilA, stn, spvC, and spiC) and ESBL genes (bla, bla, and bla) were detected by PCR. Antimicrobial susceptibility testing was carried out following CLSI guidelines. Nineteen isolates (9.5%) were confirmed as Salmonella. Serotyping revealed four serovars: S. Kentucky (52.63%), S. Typhimurium (21.05%), S. Salamae (15.79%), and S. Infantis (10.53%). All isolates carried invA and hilA, while stn and spiC were present in 84.21% and 73.68% of isolates, respectively, spvC was detected in only one isolate (5.26%). All isolates were resistant to ceftazidime, cefepime, and erythromycin. High resistance rates were also observed against amoxicillin, amoxicillin-clavulanic acid, ciprofloxacin, and doxycycline. Detection of ESBL genes revealed that blawas present in 16 isolates (84.2%), blain 6 isolates (31.6%), and blain 2 isolates (10.5%). Statistical analyses (Chi-square and Spearman's correlation tests) further confirmed significant associations between ESBL genes and both phenotypic resistance and virulence determinants, strengthening the validity of our findings. The high prevalence of virulence factors and antimicrobial resistance traits, particularly extensively drug-resistant (XDR) phenotypes and ESBL-encoding genes among Salmonella isolates from poultry, represents a critical public health concern. These findings emphasize the need for continuous molecular surveillance, improved antimicrobial stewardship, and enhanced biosecurity strategies in poultry production in Egypt.