Food Workers as a Reservoir of Extended-Spectrum-Cephalosporin-Resistant Salmonella Strains in Japan

摘要

Dissemination of extended-spectrum-cephalosporin (ESC)-resistant Salmonella, especially extended-spectrum-beta-lactamase (ESBL)-producing Salmonella, is a concern worldwide. Here, we assessed Salmonella carriage by food workers in Japan to clarify the prevalence of ESC-resistant Salmonella harboring bla(CTX-M) . We then characterized the genetic features, such as transposable elements, of bla(CTX-M)-harboring plasmids using whole-genome sequencing. A total of 145,220 stool samples were collected from food workers, including cooks and servers from several restaurants, as well as food factory workers, from January to October 2017. Isolated salmonellae were subjected to antimicrobial susceptibility testing (disk diffusion method), and whole-genome sequencing was performed for Salmonella strains harboring bla(CTX-M). Overall, 164 Salmonella isolates (0.113%) were recovered from 164 samples, from which we estimated that at least 0.113% (95% confidence interval [Cl]: 0.096 to 0.132%) of food workers may carry Salmonella. Based on this estimation, 3,473 (95% CI = 2,962 to 4,047) individuals among the 3,075,330 Japanese food workers are likely to carry Salmonella. Of the 158 culturable isolates, seven showed resistance to ESCs: three isolates harbored bla(CMY-2) and produced AmpC beta-lactamase, while four ESBL-producing isolates harbored bla(CTX-M-14) (n = 1, Salmonella enterica serovar Senftenberg) or bla(CTX-M-15) (n = 3, S. enterica serovar Haardt). bla(CTX-M-15 )was chromosomally located in the S. Haardt isolates, which also contained ISEcp1, while the S. Senftenberg isolate contained an IncFIA(HI1)/IncHI1A/IncHI1B(R27) hybrid plasmid carrying bla(CTX-M-14) along with ISEcp1. This study indicates that food workers may be a reservoir of ESBL-producing Salmonella and associated genes. Thus, these workers may contribute to the spread of bla(CTX-M) via plasmids or mobile genetic elements such as ISEcp1.