Intracellular Accumulation of Linezolid and Florfenicol in OptrA-Producing Enterococcus faecalis and Staphylococcus aureus.

Yingyu Wang,Stefan Schwarz,Yang Wang,Xi Xia,Xiaowei Li,Jianzhong Shen

doi:10.3390/molecules23123195

Abstract

The optrA gene, which confers transferable resistance to oxazolidinones and phenicols, is defined as an ATP-binding cassette (ABC) transporter but lacks transmembrane domains. The resistance mechanism of optrA and whether it involves antibiotic efflux or ribosomal protection remain unclear. In this study, we determined the MIC values of all bacterial strains by broth microdilution, and used ultra-high performance liquid chromatography-tandem quadrupole mass spectrometry to quantitatively determine the intracellular concentrations of linezolid and florfenicol in Enterococcus faecalis and Staphylococcus aureus. Linezolid and florfenicol both accumulated in susceptible strains and optrA-carrying strains of E. faecalis and S. aureus. No significant differences were observed in the patterns of drug accumulation among E. faecalis JH2-2, E. faecalis JH2-2/pAM401, and E. faecalis JH2-2/pAM401+optrA, but also among S. aureus RN4220, S. aureus RN4220/pAM401, and S. aureus RN4220/pAM401+optrA. ANOVA scores also suggested similar accumulation conditions of the two target compounds in susceptible strains and optrA-carrying strains. Based on our findings, the mechanism of optrA-mediated resistance to oxazolidinones and phenicols obviously does not involve active efflux and the OptrA protein does not confer resistance via efflux like other ABC transporters.

Highlights

Bacteria have shown an increasing ability to resist the actions of antimicrobial agents, such that the treatment of pathogenic bacterial infections has become a major challenge to public health
Aureus RN4220/pAM401 were at 4 mg/L florfenicol and 2 mg/L linezolid, respectively
In the low-dose groups, the highest accumulation was mostly observed at 10 min, and concentrations were slightly lower at 30 min and 60 min, while in the high-dose groups, accumulation commonly peaked at 30 min and declined again at

Summary

Introduction

Bacteria have shown an increasing ability to resist the actions of antimicrobial agents, such that the treatment of pathogenic bacterial infections has become a major challenge to public health. Major reported drug-resistance mechanisms include drug inactivation by enzymes [1,2], drug efflux pumps [3,4], drug target alteration or protection [5]. Active efflux pump genes have been found in Gram-positive and Gram-negative bacteria encoded on the chromosome like norB and tet38 [7], or plasmid like msr(A) [8]. Since our first report of the plasmid-mediated optrA gene in Enterococcus faecalis and Enterococcus faecium, which confers transferable resistance to phenicols and last-line antimicrobial oxazolidinone drugs, in China in 2015 [9], there have been reports of the widespread dissemination of this gene among Gram-positive bacteria [10,11,12].

Objectives

Methods

Results

Conclusion