Isolation and characterization of Salmonella enterica serovars from poultry in Egypt: a comprehensive genetic analysis of ESBLs, MCR, integron and other resistance genes.

Abstract

OBJECTIVES: Salmonella enterica is a major foodborne pathogen increasingly associated with antimicrobial resistance, particularly in poultry production. The present study aimed to investigate the prevalence and serotypes of Salmonella isolated from broiler chicks. Additionally, the recovered strains were analyzed to determine their antimicrobial susceptibility profiles and to identify the presence of genotypic resistance determinants. DESIGN: A total of 450 samples were collected from broiler chicks submitted by poultry farms and diagnostic laboratories in Mansoura, Egypt. Confirmed Salmonella isolates were serotyped and subjected to antimicrobial susceptibility testing. Colistin susceptibility was determined by the broth microdilution method (MIC). In addition, polymerase chain reaction (PCR) was employed to screen the genetic elements associated with antimicrobial resistance. RESULTS: Twenty-nine isolates (n = 29) were confirmed as Salmonella. Serotyping revealed the presence of the following Salmonella serovars: S. Kentucky (n = 10), S. Derby (n = 6), S. Typhimurium (n = 4), S. Salamae (n = 3), S. Colorado (n = 2), S. Infantis (n = 2), S. Jerusalem (n = 1), and S. Virchow (n = 1). All isolates were resistant to cefoxitin, cefepime, ceftazidime, nalidixic acid, erythromycin, and fosfomycin, while the highest susceptibility was observed to meropenem and imipenem. Eight isolates were resistant to colistin (MIC > 2 µg/mL). Molecular detection of resistance genes demonstrated the presence of bla(82.8%), bla(27.6%), bla(24.1%), bla(24.1%), bla(10.3%), and bla(3.4%), whereas blawas not detected in any of the isolates. In addition, all carbapenemase-encoding genes were not detected. Among the colistin resistance genes, only mcr-1 was detected (10.3%), while the class I integron (intI1) was detected in 96.6% of the isolates. CONCLUSIONS:  Based on serological identification, this study reports the detection of rare Salmonella enterica serovars, such as S. Colorado and S. Jerusalem, with extensive drug resistance (XDR) in broiler farms in Egypt. These isolates carried critical resistance genes, including intI1, mcr-1, and various β-lactamases. The findings underscore the urgent need for surveillance, biosecurity, and antimicrobial stewardship to protect public health and poultry production.