Molecular epidemiological characteristics and antibiotic resistance of multi-drug resistant Salmonella 1,4,5,12∶i∶- in Guangdong

  Objective  To study the characteristics of multi-drug resistance of Salmonella 1,4,5,12∶i∶- and its genetic background in Guangdong province, and provide strong support for the drug resistance surveillance of this serotype and the early warning, prevention and control of foodborne disease outbreaks in Guangdong.

  Methods  A total of 92 strains of Salmonella 1,4,5,12∶i∶- collected from the sentinel hospitals for diarrhea pathogen surveillance in Guangdong province were included in the study. Minimal broth dilution method was used to detect the minimum inhibitory concentration of strains to 27 antibacterial agents. Whole-genome sequencing was applied to study the molecular characteristics associated with antibiotic resistance. Multilocus sequence typing (MLST) and whole-genome single nucleotide polymorphisms (wgSNPs) were conducted to analyze population structure of the isolates and evolutionary relationship between the isolates and global circulating strains.

  Results  The multi-drug resistance of Salmonella 1,4,5,12:i:- was serious, with high resistance to tetracycline, ampicillin and sulfisoxazole, moderate resistance to aminoglycosides, cephalosporins, and high sensitivity to quinolones simultaneously. Resistance genes carried by the isolates were various. The drug resistance genes were consistent with overall drug-resistant phenotypes. The transmission of drug resistance genes mediated by mobile genetic elements such as IncHI2/IncHI2A, IncQ-type plasmids and insert sequences was the main mechanism of multi-drug resistance of Salmonella 1,4,5,12∶i∶-. MLST analysis showed that ST34 was the predominant clone of Salmonella 1,4,5,12∶i∶- in Guangdong. Phylogenetic analysis found that the serotype population belonged to the same evolution branch with global circulating strain, which indicated a close genetic evolutionary relationship with international circulating clone.

  Conclusion  The multi-drug resistance patterns of Salmonella 1,4,5,12∶i∶- varied in Guangdong, the drug resistance mechanism was complex, and acquired drug resistance was predominant. The multi-drug resistant Salmonella 1,4,5,12∶i∶- isolates in Guangdong showed a specific phylogenetic lineage. ST34 with a extensive antibiotic resistance pattern was predominant, which was consistent with the global trend.