Abstract:Objective: One hundred and eighteen foodborne Salmonella isolates that previously recovered from 7 provinces (cities), which including Shaanxi, Guangdong, Fujian, Shanghai, Beijing, Henan and Sichuan, were reidentified and characterized via Gram staining morphology, biochemical characterization, 16S rDNA gene sequencing; antimicrobial susceptibility; the genetic stability of β-lactam antibiotic resistance encoding genes of 12 representative isolates; for reference strain preparation for β-lactam antibiotic resistance encoding gene detection among foodborne pathogens. Methods: To reidentify the isolate, Gram stain, VITEK biochemical and MALDI-TOF MS identification, and 16S rDNA gene amplification and sequence analysis were used. The antibiotic susceptibility was tested via agar dilution method issued by the Clinical and Laboratory Standards Institute. The genetic stability of β-lactam antibiotic resistance encoding genes was determined using subculture, PCR, DNA sequencing and online BLAST software of the GenBank database. Results: The biochemical characteristics, sequence of 16S rDNA, flight mass spectrometry of proteins of 118 Salmonella were consistent with those of typical Salmonella. Among 118 Salmonella isolates, antibiotic resistance was commonly found to ampicillin (100.00%), sulfisoxazole (100.00%) and ceftiofur (100.00%); more than 50% of the isolates resisted to 7 kinds of antibiotics. blaTEM-1 (64.41%) was most frequently detected among the isolates, the detection rates of blaCTX-M-55, blaOXA-1, blaCTX-M-3, blaCTX-M-15, blaTEM-116, blaCTX-M-123 and blaCTX-M-64 positive isolates were 50.85%, 16.10%, 15.25%, 1.69%, 1.69%, 0.85% and 0.85%, respectively. No loss or mutation was detected among the base or gene fragment of β-lactam antibiotic resistance encoding genes of the 12 screened representative Salmonella isolates during subcultures. Conclusion: Results of 4 different identifications consisted to those of the typical Salmonella should to be; the antibiotic resistance encoding genes blaTEM-1, blaCTX-Ms and blaOXA-1 carried by the isolates could be stably inherited during subculture, the 12 representative Salmonella were verified to have the potentiality to produce reference strain for β-lactam antibiotic resistance encoding gene detection.