Emergence of -Harboring Serovar Sinstorf Type ST155 Isolated From Patients With Diarrhea in Jiangsu, China.

This study analyzed the antimicrobial resistance phenotypes and mechanisms of quinolone, cephalosporins, and colistin resistance in nontyphoidal from patients with diarrhea in Jiangsu, China. A total of 741 nontyphoidal isolates were collected from hospitals in major cities of Jiangsu Province, China between 2016 and 2017. Their susceptibility to commonly used antibiotics was evaluated by broth micro-dilution and sequencing analysis of resistance genes screened by a PCR method. For positive isolates, genetic relationship study was carried out by pulsed-field gel electrophoresis and multiloci sequence typing analysis. The transferability of these plasmids was measured with conjugation experiments and the genetic locations of were analyzed by pulsed-field gel electrophoresis profiles of S1-digested genomic DNA and subsequent Southern blot hybridization. Among 741 nontyphoidal isolates, the most common serotypes identified were Typhimurium (=257, 34.7%) and Enteritidis (=127, 17.1%), and the isolates showed 21.7, 20.6, and 5.0% resistance to cephalosporins, ciprofloxacin, and colistin, respectively. Among the 335 nalidixic acid-resistant , 213 (63.6%) and 45 (13.4%) had at least one mutation in and . Among the plasmid-borne resistance, (85; 41.9%) and (75; 36.9%) were the most common quinolone resistance (PMQR) genes, while (=35) and (=46) were found to be dominant extended-spectrum beta-lactamase (ESBL) genes in nontyphoidal . In addition, eight -harboring strains were detected since 2016 and they were predominate in children under the age of 7years. Conjugation assays showed the donor strain has functional and transferable colistin resistance and Southern blot hybridization revealed that was located in a high molecular weight plasmid. In nontyphoidal , there is a rapidly increasing trend of colistin resistance and this is the first report of patients harboring -positive with a new ST type ST155 and new serotype Sinstorf. These findings demonstrate the necessity for cautious use and the continuous monitoring of colistin in clinical applications.