AUTHOR=Liu Guoye , Qian Huimin , Lv Jingwen , Tian Benshun , Bao Changjun , Yan Hong , Gu Bing 

TITLE=Emergence of mcr-1-Harboring Salmonella enterica Serovar Sinstorf Type ST155 Isolated From Patients With Diarrhea in Jiangsu, China

JOURNAL=Frontiers in Microbiology

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2021.723697

DOI=10.3389/fmicb.2021.723697

ISSN=1664-302X

ABSTRACT=<p><bold>Background:</bold> This study analyzed the antimicrobial resistance phenotypes and mechanisms of quinolone, cephalosporins, and colistin resistance in nontyphoidal <italic>Salmonella</italic> from patients with diarrhea in Jiangsu, China.</p><p><bold>Methods:</bold> A total of 741 nontyphoidal <italic>Salmonella</italic> 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 <italic>mcr-1</italic> 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 <italic>mcr-1</italic> were analyzed by pulsed-field gel electrophoresis profiles of S1-digested genomic DNA and subsequent Southern blot hybridization.</p><p><bold>Results:</bold> Among 741 nontyphoidal <italic>Salmonella</italic> isolates, the most common serotypes identified were <italic>S.</italic> Typhimurium (<italic>n</italic>=257, 34.7%) and <italic>S.</italic> Enteritidis (<italic>n</italic>=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 <italic>Salmonella</italic>, 213 (63.6%) and 45 (13.4%) had at least one mutation in <italic>gyrA</italic> and <italic>parC</italic>. Among the plasmid-borne resistance, <italic>qnrS1</italic> (85; 41.9%) and <italic>aac(6')-Ib-cr4</italic> (75; 36.9%) were the most common quinolone resistance (PMQR) genes, while <italic>bla</italic><sub>CTX-M-14</sub> (<italic>n</italic>=35) and <italic>bla</italic><sub>CTX-M-55</sub> (<italic>n</italic>=46) were found to be dominant extended-spectrum beta-lactamase (ESBL) genes in nontyphoidal <italic>Salmonella</italic>. In addition, eight <italic>mcr-1</italic>-harboring strains were detected since 2016 and they were predominate in children under the age of 7years. Conjugation assays showed the donor <italic>Salmonella</italic> strain has functional and transferable colistin resistance and Southern blot hybridization revealed that <italic>mcr-1</italic> was located in a high molecular weight plasmid.</p><p><bold>Conclusion:</bold> In nontyphoidal <italic>Salmonella</italic>, there is a rapidly increasing trend of colistin resistance and this is the first report of patients harboring <italic>mcr-1</italic>-positive <italic>Salmonella</italic> with a new ST type ST155 and new serotype <italic>S.</italic> Sinstorf. These findings demonstrate the necessity for cautious use and the continuous monitoring of colistin in clinical applications.</p>