Rapid identification of bacterial polymyxin resistance mechanisms in Enterobacterales in negative ion mode by MALDI-TOF MS
Objective To investigate the main resistance mechanism of polymyxin-resistant Enterobacterales in Xuzhou and its rapid detection technology,and provide a comprehensive laboratory basis for the rational and standardized use of polymyxin in the clinic.Methods Polymyxin-resistant Enterobacterales strains isolated from November 2022 to November 2023 at the Affiliated Hospital of Xuzhou Medical University were collected.The polymyxin-resistant regulatory genes pmrA,pmrB,phoP,phoQ,mgrB,and mcr-1 were detected by PCR amplification,and the displacement of the lipid A basal peaks was detected by matrix-assisted laser desorption ionization time-of-flight mass spectrometry(MALDI-TOF MS)in negative ion mode.Results A total of 24 non-repetitive polymyxin-resistant Enterobacterales strains were collected,including 19 strains of Klebsiella pneumoniae and 5 strains of Escherichia coli.Genetic testing showed that all of the Escherichia coli were mcr-1 gene-positive strains,while four of the Klebsiella pneumoniae strains carried the mcr-1 gene,three strains had premature termination of the mgrB gene,six strains had the G256R mutation in the pmrB gene,another two strains had both the G256R and A246T mutations in thepmrB gene,two strains had the L26Q and A351D mutations in the phoQ gene,one strain had the D191G mutation in the phoP gene,and one strain not only carried the mcr-1 gene but also had the base 137C→G mutation in mgrB.MALDI-TOF MS in negative ion mode showed that all mcr-1 positive strains had a+123 m/z shift in the natural lipid A base peak,while all strains with mutations in the gene on the chromosome had a+131 m/z shift in the natural lipid A base peak.Conclusions There were two main resistance mechanisms to polymyxin in Enterobacterales bacteria in Xuzhou,i.e.,carrying the mcr-1 gene and the mutation of the regulatory gene of the two-component system,and MALDI-TOF MS in negative ion mode could realize the detection of the polymyxin-resistant phenotypes of the main Enterobacterales bacteria due to the modification of the lipopolysaccharides,as well as the identification of their resistance mechanisms.
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