Extended-spectrum β-lactamases (ESBLs)-producing Salmonella is considered a serious concern to public health worldwide. However, limited information is available on ESBLs-producing Salmonella in retail chicken products in China. The objective of this study was to characterize ESBLs-producing Salmonella isolates from retail chickens in China. A total of 890 Salmonella isolates from retail chicken carcasses collected from 4 provinces were firstly screened for ESBLs-production phenotype via the double-disk synergy test method. A total of 96 (10.8%, n=890) ESBLs-producing Salmonella were identified and subjected to PFGE analysis, characterization for the presence of ESBLs encoding genes, transposons, carbapenemase and virulence genes. A total of 59 PFGE profiles were detected in these 96 isolates, among which 57.3% were found to harbor blaTEM-1, whereas 30.2%, 24.0%, 18.8% and 7.3% were carrying blaOXA-1, blaCTX-M-15, blaCTX-M-3 and blaPSE-1 genes, respectively. Moreover, 42 (43.8%) isolates co-carried 2 ESBLs-producing genes, and two (2.1%) isolates co-carried 3 genes. Furthermore, 24 (25.0%) ESBLs-producing isolates carried VIM and 10 (10.4%) carried KPC encoding genes that closely associated with carbapenems resistance. Eighty-eight isolates harbored transposons ranging from 4.2% for Tn903 to 76.0% for Tn21. Out of the 88 Salmonella that harbored transposons, 25%, 22.7%, 23.9%, 10.2% and 1.1% of isolates were found to carry 2, 3, 4, 5 and 6 transposons, respectively. The minimum inhibitory concentration (MIC) values for cephalosporins (ceftriaxone, cefoperazone and cefoxitin) to ESBLs-producing isolates were from 4 to 1024μg/mL, for nalidixic acid were from 64 to 512μg/mL, for fluoroquinolones (ciprofloxacin, levofloxacin and gatifloxacin) were from 4 to 256μg/mL. Twenty-nine virulence genes were detected in the 96 ESBLs-producing isolates with 2.1% harbored spvR (lowest) and 90.6% harbored marT and steB (highest). All isolates carried at least one virulence gene, 83.3% of the isolates co-carried ≥10, 17.7% co-carried ≥15, and 1.0% co-carried 23 virulence genes. Interestingly, 16.7% of the isolates resistant to >12 antibiotics tested and shown to carry >4 transposons and 10 virulence genes. Our findings indicated that ESBLs-producing Salmonella isolated from retail chicken meat in China were highly resistant to antibiotics, frequently harbored transposons, virulence genes, carbapenems hydrolysis enzymes and ESBLs encoding genes. These isolates can pose a significant public health risk.

Extended-spectrum beta-lactamases (ESBL)-producing Salmonella enterica have been reported worldwide. However, research on foodborne ESBL-producing Salmonella has been rarely conducted. One hundred and thirty eight ceftriaxone or/and cefoperazone-resistant Salmonella strains recovered from retail foods in Shaanxi and Henan Province, China, were screened for ESBL. The ESBL-producing strains were further characterized for antimicrobial resistance, pulse field gel electrophoresis (PFGE) profiles, and the presence of blaTEM, blaSHV, blaOXA, blaCTX-M, and blaPSE. The transferability of ESBL encoding genes to a susceptible Escherichia coli strain was also investigated. Thirty (21.7%) isolates were identified as ESBL positive and belonged to S. enterica serovars Indiana, Shubra, Typhimurium, and Enteritidis. S. Indiana and S. Shubra isolates were firstly identified in ESBL-producing strains. Great genetic diversity was seen among these ESBL-producing strains. Nucleotide sequence analysis revealed that blaTEM-1B was the only ESBL-encoding gene among the genes tested and was detected in 26 of 30 strains and was carried in the conjugative plasmids. The blaTEM-1B gene was transferable through conjugation at rates ranging from 4.71 × 10(-7) to 7.55 × 10(-6) transconjugant per recipient cell. This study provides the evidence of foodborne ESBL-producing Salmonella, and the transferability of plasmid harboring ESBL-encoding genes could possibly contribute to the dissemination of ESBL.