Mechanism of Eravacycline Resistance in Clinical Enterococcus faecalis Isolates From China

Abstract

Opportunistic infections caused by multidrug-resistant <i>Enterococcus faecalis</i> strains are a significant clinical challenge. Eravacycline (Erava) is a synthetic fluorocycline structurally similar to tigecycline (Tige) that exhibits robust antimicrobial activity against Gram-positive bacteria. This study investigated the <i>in vitro</i> antimicrobial activity and heteroresistance risk of Eravacycline (Erava) in clinical <i>E. faecalis</i> isolates from China along with the mechanism of Erava resistance. A total of 276 non-duplicate <i>E. faecalis</i> isolates were retrospectively collected from a tertiary care hospital in China. Heteroresistance to Erava and the influence of tetracycline (Tet) resistance genes on Erava susceptibility were examined. To clarify the molecular basis for Erava resistance, <i>E. faecalis</i> variants exhibiting Erava-induced resistance were selected under Erava pressure. The relative transcript levels of six candidate genes linked to Erava susceptibility were determined by quantitative reverse-transcription PCR, and their role in Erava resistance and heteroresistance was evaluated by <i>in vitro</i> overexpression experiments. We found that Erava minimum inhibitory concentrations (MICs) against clinical <i>E. faecalis</i> isolates ranged from ≤0.015 to 0.25 mg/l even in strains harboring Tet resistance genes. The detection frequency of Erava heteroresistance in isolates with MICs ≤ 0.06, 0.125, and 0.25 mg/l were 0.43% (1/231), 7.5% (3/40), and 0 (0/5), respectively. No mutations were detected in the 30S ribosomal subunit gene in Erava heteroresistance-derived clones, although mutations in this subunit conferred cross resistance to Tige in Erava-induced resistant <i>E. faecalis</i>. Overexpressing RS00630 (encoding a bone morphogenetic protein family ATP-binding cassette transporter substrate-binding protein) in <i>E. faecalis</i> increased the frequency of Erava and Tige heteroresistance, whereas RS12140, RS06145, and RS06880 overexpression conferred heteroresistance to Tige only. These results indicate that Erava has potent <i>in vitro</i> antimicrobial activity against clinical <i>E. faecalis</i> isolates from China and that Erava heteroresistance can be induced by RS00630 overexpression.