Characteristics of Antimicrobial-Resistant Strains and Identification of Related Antimicrobial Resistance Gene Mutations.

Multidrug-resistant (MDR) strains have become a great threat to public health. The purpose of this study was to investigate differences in biological characteristics and antimicrobial resistance gene (ARG) mutations of that displayed different levels of antimicrobial resistance. The susceptibility of 74 strains to 9 common antimicrobials was investigated, of which 88% were resistant to 3-4 antimicrobials and 3% to 5-7 antimicrobials. Interestingly, only 9% were resistant to 1-2 antimicrobials. The MDR strains possessed longer growth lag time than the non-MDR strains and displayed weaker swimming abilities. Whole genome sequencing was performed on strains VP41, VP44, 460, and 469 that were resistant to two to three classes of antimicrobials. ARGs were identified and compared with that of reference strain ATCC17802, and some important mutations were deduced. The Val189Ile mutation emerged in gene of a single strain. Besides, the nonsynonymous mutations existed in four ARGs in different strains, including CatB (Pro165Ser, Gly208Asp), VmeA (Ile313Thr), VmeC (Glu329Ala), and VmeD (Asn205Ser). These results linked resistance gene mutations to enhance resistance in strains and provide a reference for more effective monitoring and prevention of infections.