Emergence of <i>optrA</i>-Mediated Linezolid-Nonsusceptible <i>Enterococcus faecalis</i> in a Tertiary Care Hospital

Abstract

This study investigated resistance mechanisms and epidemiology of emerging linezolid-nonsusceptible <i>Enterococcus faecalis</i> (LNSEF) in a tertiary care hospital. LNSEF isolated from clinical samples were collected from November 2017 to June 2019. The isolates were investigated for linezolid resistance and the associated molecular mechanisms, including mutations of 23S rRNA domain V and acquisition of the <i>cfr</i> or <i>optrA</i> resistance gene. We used pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing for the molecular typing of the isolates. Among 4,318 <i>E. faecalis</i> isolates, 10 (0.23%) were linezolid-nonsusceptible. All LNSEF isolates were <i>optrA</i>-positive and <i>cfr</i>-negative. Of these isolates, five were sequence type (ST) 476, two ST585, one ST16, one ST16-like, and one ST480. Six LNSEF isolates obtained in the first year clustered to three types in the PFGE analysis: two ST476 isolates of type A, two ST585 isolates of type B, and two ST16 or ST16-like isolates of type C. Seven cases were of community-onset and three were hospital acquired, but total of eight were healthcare-associated including five community-onset. None of the patients had a history of linezolid treatment, and in one patient, we detected linezolid-susceptible <i>E. faecalis</i> one month before LNSEF detection. In conclusion, heterogenous clones of <i>optrA</i>-positive LNSEF emerged in the hospital mainly via community-onset.