Colistin Heteroresistance in Klebsiella Pneumoniae Isolates and Diverse Mutations of PmrAB and PhoPQ in Resistant Subpopulations.

Hae Suk Cheong,So Yeon Kim,Kyong Ran Peck,Yu Mi Wi,Kwan Soo Ko

doi:10.3390/jcm8091444

Abstract

Heteroresistance may pose a threat to the prognosis of patients following colistin treatment. We investigated colistin heteroresistance in Klebsiella pneumoniae isolates from South Korea. Among 252 K. pneumoniae blood isolates, 231 were susceptible to polymyxins. Heteroresistance to colistin was determined using population analysis profiles, disk diffusion assays, and E-test strip tests for the susceptible isolates. As a result, we identified three colistin-heteroresistant K. pneumoniae isolates belonging to separate clones (ST11, ST461, and ST3217) by multilocus sequence typing analysis. Two colistin-resistant subpopulations were selected from each heteroresistant isolate in either disk diffusion testing or E-testing. Two resistant subpopulations from the same isolate exhibited different amino acid substitutions in the two-component regulatory systems PmrAB and PhoPQ. An in vitro time–kill assay showed that meropenem combined with colistin had a 1× minimum inhibitory concentration bactericidal effect against a multidrug-resistant, colistin-heteroresistant isolate.

Highlights

Klebsiella pneumoniae is one of the most clinically significant pathogens belonging to the family Enterobacteriaceae
The colistin minimum inhibitory concentration (MIC) of ≥64 μg/mL in the resistant subpopulations persevered after serial subculture in colistin-free media, indicating their stable feature of colistin resistance
According to MLST analysis, the three colistin-heteroresistant K. pneumoniae blood isolates belonged to different clones—ST3217 (S1703-35), ST461 (S1703-109), and ST11 (S1703-112)—which were clones not be strictly associated with colistin resistance

Summary

Introduction

Klebsiella pneumoniae is one of the most clinically significant pathogens belonging to the family Enterobacteriaceae. It is an important pathogen in community- and hospital-acquired infections [1]. Colistin and polymyxin B are important therapeutic options for treating infections caused by carbapenem-resistant K. pneumoniae [6,7]. Resistance to colistin generally involves mutations in chromosomal genes. Acquired resistance to polymyxins in strains such as K. pneumoniae and Escherichia coli involves mutations in the two-component regulatory systems PmrAB and PhoPQ or alterations to the negative regulator of PhoPQ, MgrB [10,11]

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Conclusion