Epidemiology of bla(CTX-M)-Positive Salmonella Typhimurium From Diarrhoeal Outpatients in Guangdong, China, 2010–2017

Salmonella enterica can lead to intestinal diarrhea, and the emergence and spread of cephalosporin-resistant Salmonella have brought great challenges to clinical treatment. Therefore, this study investigated the prevalence and transmission of bla(CTX-M) genes among S. Typhimurium from diarrhoeal outpatients in Guangdong, China, from 2010 to 2017. A total of 221 bla(CTX-M)-positive isolates were recovered from 1,263 S. Typhimurium isolates from the facal samples of diarrhoea patients in 45 general hospitals from 11 cities. The most popular CTX-M gene was bla(CTX-M-55) (39.6%, 72/182) in the CTX-M-1 group, followed by bla(CTX-M-14) (22.5%, 41/182) and bla(CTX-M-65) (19.2%, 35/182) in the CTX-M-9 group. The isolates that carried bla(CTX-M-9G) had significantly higher resistance rates to multiple antibacterials compared with bla(CTX-M-1G) (p < 0.01). Meanwhile, PFGE analysis not only showed the clonal transmission of bla(CTX-M-55/14/65)-positve isolates of diarrhoeal outpatients’ origins from different hospitals in Guangdong province, but also the characteristic of bla(CTX-M-55/14/65)-positve isolates’ bacterial persistence. Multilocus sequence typing (MLST) analysis indicated that these S. Typhimurium isolates possessed ST34 and ST19. Furthermore, genomic Beast phylogenomic analysis provided the evidence of a close relationship of bla(CTX-M)-positive S. Typhimurium isolates between the outpatients and pork. Most bla(CTX-M-55/14/65) genes were transmitted by non-typeable or IncI1/IncFII/IncHI2 plasmids with the size of ranging from ~80 to ~280 kb. Moreover, whole-genome sequencing (WGS) analysis further revealed that bla(CTX-M-55/14/65) coexisted with other 25 types of ARGs, of which 11 ARGs were highly prevalent with the detection rates >50%, and it first reported the emergence of bla(TEM-141) in S. Typhimurium. This study underscores the importance of surveillance for bla(CTX-M)-positive microbes in diarrhea patients.