Abstract
Salmonella enterica subsp. enterica serovar 1,4,[5],12:i:- is a monophasic variant of Salmonella Typhimurium, which has recently been recognized as an emerging cause of infection worldwide. This bacterium has also ranked among the four most frequent serovars causing human salmonellosis in China. However, there are no reports on its contamination in Chinese food. Serotyping, polymerase chain reaction, antibiotic resistance, virulotyping, and multilocus sequence typing (MLST) assays were used to investigate the prevalence of this serological variant in food products in China, and to determine phenotypic and genotypic difference of monophasic isolates and Salmonella Typhimurium isolated over the same period. Salmonella 1,4,[5],12:i:- was prevalent in various food sources, including beef, pork, chicken, and pigeon. The study also confirmed the high prevalence (53.8%) of resistance to ampicillin, streptomycin, sulfonamides, and tetracycline in Salmonella 1,4,[5],12:i:-, which was higher than that in Salmonella Typhimurium. Moreover, Salmonella 1,4,[5],12:i:- isolates in our study were different from Salmonella Typhimurium isolates by the absence of three plasmid-borne genes (spvC, pefA, and rck) and the presence of gipA in all isolates. All Salmonella 1,4,[5],12:i:- isolates demonstrated MLST pattern ST34. Genomic deletions within the fljBA operon and surrounding genes were only found in Salmonella 1,4,[5],12:i:- isolates, with all isolates containing a deletion of fljB. However, hin and iroB were identified in all Salmonella 1,4,[5],12:i:- isolates. Three different deletion profiles were observed and two of them were different from the reported Salmonella 1,4,[5],12:i:- clones from Spain, America, and Italy, which provided some new evidence on the independent evolution of the multiple successful monophasic clones from Salmonella Typhimurium ancestors. This study is the first report of Salmonella 1,4,[5],12:i:- in food products from China. The data are more comprehensive and representative, providing valuable information for epidemiological studies, risk management, and public health strategies.
Highlights
Salmonella are often acquired from contaminated food, and are important causes of gastroenteritis and bacteremia, posing a worldwide threat to public health [1]
The objective of this study was to characterize Salmonella 1,4,[5],12:i:- isolates collected from food samples across China from 2011–2014, and compare these isolates with Salmonella Typhimurium isolated in the same period to better understand the prevalence, phenotypic and genetic diversity, and susceptibility to antimicrobials of this serovar in China
Strains were definitively assigned to Salmonella Typhimurium or Salmonella 1,4,[5],12:i:- using the duplex-PCR assay developed by Tennant et al [24] and recommended by the European Food Safety Authority (EFSA) Panel on Biological Hazards [4]
Summary
Salmonella are often acquired from contaminated food, and are important causes of gastroenteritis and bacteremia, posing a worldwide threat to public health [1]. Enterica serovar 1,4,[5],12:i:- has ranked among the four most frequent serovars causing human salmonellosis in China [2]. It is one of the most common serovars isolated from humans and foods in several other countries [4,5]. This atypical serovar, lacking the phase 2 flagellar antigen [6,7], has become increasingly important since the mid-1990s worldwide. It is designated as a monophasic variant of Salmonella Typhimurium, with antigenic and genotypic similarities [6,8,9,10]
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