Epidemiological characteristics and genetic structure of linezolid-resistant Enterococcus faecalis

The aim of this study was to investigate the mechanism of linezolid resistance and evaluate the risk factors for linezolid-resistant Enterococcus faecalis (LZR-Efa) infections.

A total of 730 E. faecalis isolates were collected, and whole-genome sequencing and bioinformatics analysis were performed. Meanwhile, risk factors related to linezolid resistance were analyzed by binary logistic regression.

Twenty-six LZR-Efa were isolated from various clinical samples, and 24 isolates were multidrug resistant. Four isolates were daptomycin nonsusceptible, while all LZR-Efa were susceptible to vancomycin. Thirteen different sequence types (STs) were identified, and the most prevalent type was ST16 (23.1%). The genes dfrE, lsaA, and emeA were identified in all isolates. A total of 23 E. faecalis were positive for optrA gene, and six amino acids mutations were identified among 18 LZR-Efa in OptrA. The 23S rRNA mutation was found in 16 LZR-Efa isolates. However, the presence of cfr was not identified. Furthermore, there were 41 virulence genes detected, and 10 genes (ace, bopD, cpsA, cpsB, ebpB, ebpC, efaA, fss1, fss2, and srtC) were found in all isolates. A total of nine isolates were positive for multiple virulent factors (ace, asa1, cylA, efaA, esp, and gelE). There was no difference in the number of virulence factors among different specimens (P=0.825). It is of note that all patients had not been prescribed linezolid or traveled abroad previously. Moreover, previous use of carbapenems was a risk factor for LZR-Efa infections.

The main trends of LZR-Efa, with lower level of resistance, were sporadic mainly in the department of surgery. optrA and 23S rRNA were the main resistance mechanisms. In addition, carbapenems use was an independent predictor of LZR-Efa infections.