Genomic Epidemiology of ST34 Monophasic Salmonella enterica Serovar Typhimurium from Clinical Patients from 2008 to 2017 in Henan, China

Abstract

Salmonella enterica serovar 4,[5],12:i:- (S. 4,[5],12:i:-) is a monophasic variant of Salmonella enterica serovar Typhimurium that has emerged as a global serovar causing public health concern. To date, the epidemiology and genomic characterization of this pathogen in China have not been well described. We investigated the prevalence, antimicrobial resistance (AMR) phenotypes, and population genomics of sequence type 34 (ST34) S. 4,[5],12:i:- among cases of human salmonellosis in Henan Province, China. A total of 100 ST34 S. 4,[5],12:i:- isolates were studied from 2008 to 2017 and found mostly resistant to ampicillin (AMP), streptomycin (STR), sulfonamides (SUL), and tetracycline (TET) (ASSuT). Bayesian phylogenetic analysis demonstrated that isolates identified in China were mostly related to the European lineage and evolved into two major clades with different resistance genes and plasmid profiles. Notably, clade 1 showed a significantly higher rate of mutations in gyrA and plasmid-mediated quinolone resistance genes. The carrying of the resistance-containing region (encoding R-type ASSuT), including blaTEM-1B (conferring resistance to AMP), strAB (STR), sul2 (SUL), and tet(B) (TET) inserted into the fljBA operon, was responsible for most of the monophasic variants in clade 2. IncHI2 plasmids were the dominant multi-drug resistance mobile genetic elements accounting for the transmission of acquired resistance genes in this serovar, and these were more prevalent in clade 1. Our findings highlighted the increasing prevalence of multi-drug resistant S. 4,[5],12:i:- in China, along with the differential characteristics of resistance gene acquisition among various lineages. Based on our data, control measures are required to address the spread of this zoonotic pathogen. Further owing to its potential origin in food-producing animals, a “One Health” approach, should be implemented to support surveillance whilst informing interventional strategies.

Keywords

• Salmonella Typhimurium monophasic variant
• ST34
• Prevalence
• Phylogenetic analysis
• Chinese lineages