First emergence of acrAB and oqxAB mediated tigecycline resistance in clinical isolates of Klebsiella pneumoniae pre-dating the use of tigecycline in a Chinese hospital.

Xue Zhong,Dongke Chen,Xin Hu,Haijian Zhou,Hongtao Xu,Gang Cheng,Qijing Zhang

doi:10.1371/journal.pone.0115185

Abstract

Tigecycline is one of the few therapeutic options for treating infections caused by some multi-drug resistant pathogens, such as Klebsiella pneumoniae. However, tigecycline-resistant K. pneumoniae has been discovered recently in China. From 2009 to 2013, nine tigecycline-resistant K. pneumoniae isolates were identified in our hospital. Six of nine strains were identified before using tigecycline. To investigate the efflux-mediated resistance mechanisms of K. pneumoniae, the expression of efflux pump genes (acrA, acrB, tolC, oqxA and oqxB) and pump regulators (acrR, marA, soxS, rarA, rob and ramA) were examined by real-time RT-PCR. Molecular typing of the tigecycline resistant strains was performed. ST11 was the predominant clone of K. pneumoniae strains, while ST1414 and ST1415 were novel STs. Efflux pump inhibitor (EPI)-carbonyl cyanide chlorophenylhydrazone (CCCP) was able to reverse the resistance patterns of 5 resistant K. pneumoniae strains. In comparison with strain A111, a tigecycline-susceptible strain (negative control), we found that the expression levels of efflux pump genes and pump regulators were higher in a majority of resistant strains. Higher expression levels of regulators rarA (2.41-fold, 9.55-fold, 28.44-fold and 18.31-fold, respectively) and pump gene oqxB (3.87-fold, 31.96-fold, 50.61-fold and 29.45-fold, respectively) were observed in four tigecycline resistant strains (A363, A361, A368, A373, respectively). Increased expression of acrB was associated with ramA and marA expression. To our knowledge, studies on tigecycline resistance mechanism in K. pneumoniae are limited especially in China. In our study, we found that both efflux pump AcrAB-TolC and OqxAB contributed to tigecycline resistance in K. pneumoniae isolates.

Highlights

A derivative of minocycline, tigecycline, is a new class of glycylcyclines
TaqMan probe labeled with an FAM dye at the 59 end and a minor groove binder (MGB) and nonfluorescent quencher (NFQ) at the 39 end. doi:10.1371/journal.pone.0115185.t002
The results of molecular typing suggest that the predominant clone of K. pneumoniae strains was ST11

Summary

Introduction

A derivative of minocycline, tigecycline, is a new class of glycylcyclines. It exhibits a broad-spectrum of activity against most of Gram-positive, Gram-negative pathogens , anaerobes, and ‘atypical’ bacteria [1]. Tigecycline-resistance has emerged recently in different pathogens such as Acinetobacter baumannii, Klebsiella pneumoniae and Enterobacteriaceae, especially in multidrug-resistant (MDR) strains. Emergence of non-susceptibility to tigecycline has been reported in A. baumannii and K. pneumoniae in Mainland China [4, 5]. We present nine cases of tigecycline-resistant K. pneumoniae in Mainland China. The main purpose of this study was to investigate whether similar mechanisms existed in the resistant strains isolated from Mainland China or whether there are other reasons for this tigecycline resistance

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