Colistin Heteroresistance among Extended Spectrum β-lactamases-Producing Klebsiella pneumoniae

Felipe Morales-León,Andrés Opazo-Capurro,Celia A Lima,Gerardo González-Rocha,Helia Bello-Toledo

doi:10.3390/microorganisms8091279

Abstract

Colistin-heteroresistant (CST-HR) Enterobacterales isolates have been identified recently, challenging the clinical laboratories since routine susceptibility tests fail to detect this phenotype. In this work we describe the first CST-HR phenotype in extended-spectrum β-lactamase (ESBL)-producing Klebsiella pneumoniae isolates in South America. Additionally, we determine the genomic mechanisms of colistin heteroresistance in these strains. The CST-HR phenotype was analyzed by the population analysis profile (PAP) method, and mutations associated with this phenotype were determined by whole-genome sequencing (WGS) and the local BLAST+ DB tool. As a result, 8/60 isolates were classified as CST-HR according to the PAP method. From WGS, we determined that the CST-HR isolates belong to three different Sequence Types (STs) and four K-loci: ST11 (KL15 and KL81), ST25 (KL2), and ST1161 (KL19). We identified diverse mutations in the two-component regulatory systems PmrAB and PhoPQ, as well as a disruption of the mgrB global regulator mediated by IS1-like and IS-5-like elements, which could confer resistance to CST in CST-HR and ESBL-producing isolates. These are the first descriptions in Chile of CST-HR in ESBL-producing K. pneumoniae isolates. The emergence of these isolates could have a major impact on the effectiveness of colistin as a “last resort” against these isolates, thus jeopardizing current antibiotic alternatives; therefore, it is important to consider the epidemiology of the CST-HR phenotype.

Highlights

In recent years, the prevalence of multidrug-resistant (MDR) Enterobacterale isolates in clinical settings has been increasing alarmingly
A novel CST-resistance mechanism has been described in K. pneumoniae ST11, ST29, and ST258 lineages, which is related to CrrAB mutations, similar to PhoPQ or PmrAB alterations [10,11]
Sixty ESBL-producing K. pneumoniae determined by a combined disc test and CST-susceptible isolates (CST-MIC50 = 1 μg/mL) recovered from seven different Chilean hospitals were included

Summary

Introduction

The prevalence of multidrug-resistant (MDR) Enterobacterale isolates in clinical settings has been increasing alarmingly. Among this group, extended-spectrum β-lactamase (ESBL)-producers and carbapenem-resistant Klebsiella pneumoniae represent a serious threat to public health [1,2]. Alterations in mgrB due to deletion or disruption mediated by IS1-like, IS3-like, and IS5-like elements are the most important CST-HR mechanisms in K. pneumoniae In this sense, mgrB is a conserved gene 141 nucleotides in length, which encodes a small transmembrane protein of 47 amino acids that exerts a negative feedback on the PhoPQ and PmrAB systems [8,9]. CST-HR in K. pneumoniae was described previously [14,15,16,17,18] in clinical highly resistant strains, and this phenotype was related to an increase in morbidity and mortality [14], mainly associated with a loss of colistin activity

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