Occurrence, antimicrobial resistance, and molecular characteristics of Salmonella enterica serovar 1,4,[5],12:i:- from food and patients in China

Abstract

Salmonella enterica serovar Typhimurium monophasic variant 1,4,[5],12:i:- is increasingly responsible for human infections worldwide. However, studies assessing the prevalence and epidemiological characteristics of this emerging serovar are lacking in China. Here, a collection of 125 S. Typhimurium-like strains derived from food and patients in China between 2011 and 2019 were analyzed to investigate the occurrence ratio of S. 1,4,[5],12:i:-. Among them, 23.2% (22/95) of food-related isolates and 70.0% (21/30) of human isolates were assigned as S. 1,4,[5],12:i:-. Only two strains were sequence type (ST) 19; the rest all belonged to ST34. These isolates were further divided into 29 multiple locus variable-number tandem repeat analysis (MLVA) profiles, with the same dominant profile present in both food-source and human isolates. More than 90.0% of S. 1,4,[5],12:i:- isolates were multidrug-resistant. The high prevalence of blaCTX-M (33.3%, 7/21) in extended-spectrum β-lactamase-producing S. 1,4,[5],12:i:- isolates from patients identified here will raise clinical concern over human salmonellosis treatment. Twelve different deletion types of the fljAB operon region associated with the loss of phase 2 flagellar antigen were identified. These results suggested that the Chinese S. 1,4,[5],12:i:- strains consist of multiple distinct clones and their high rates of prevalence and multidrug resistance could constitute potential risks to public health.