Molecular mechanism of colistin resistance mediated by mcr-1 and pmrAB genes in Escherichia coli / 中华微生物学和免疫学杂志

ABSTRACT

Objective To investigate the molecular mechanism of colistin resistance mediated by mcr-1and pmrAB genes in clinical Escherichia coli ( E. coli) isolates. Methods A total of 1988 clinical E. coli isolates were collected from the First People′s Hospital of Shangqiu from 2010 to 2017 and screened for colistin-resistant isolates using agar dilution method. The minimum inhibitory concentrations ( MICs) of nine common clinical antibiotics were determined using broth microdilution method. PCR and sequencing analysis were performed to detect the colistin resistance genes of mcr-1 and pmrAB. Conjugation experiments were used to test the transferability of the plasmid carrying mcr-1 gene. S1-PFGE and Southern blot were used to locate the plasmid carrying mcr-1. All colistin-resistant E. coli isolates were typed by multilocus se-quence typing ( MLST) . Results Six colistin-resistant E. coli isolates were obtained by agar dilution meth-od. The results of susceptibility testing showed that all of the six isolates were multidrug resistant. PCR and sequencing analysis revealed that four out of the six strains carried mcr-1 gene, and the other two isolates both had an amino acid substitution (L167P) caused by pmrB gene mutation. The results of conjugation ex-periments, S1-PFGE and Southern hybridization analysis showed that the plasmids of four mcr-1 gene-posi-tive E. coli strains were located on a conjugative plasmid about 60 kb in length. MLST analysis classified the six isolates into six distinct sequence types ( STs) . Conclusion This study suggested that mcr-1 gene and mutations in pmrAB gene were the main mechanisms mediating the resistance of E. coli to colistin. In clinical practice, the occurrence and spread of colistin-resistant E. coli should be further monitored, and the rational use of antibiotics should be promoted to prevent the spread of colistin-resistant strains.