Ann Lab Med 2020; 40(4): 321-325  https://doi.org/10.3343/alm.2020.40.4.321
Emergence of optrA-Mediated Linezolid-Nonsusceptible Enterococcus faecalis in a Tertiary Care Hospital
Kuenyoul Park, M.D.1, Yun Sil Jeong, M.T.1, Jeonghyun Chang, M.D.2, Heungsup Sung, M.D.1, and Mi-Na Kim, M.D., Ph.D.1
1Department of Laboratory Medicine, University of Ulsan College of Medicine and Asan Medical Center, Seoul, Korea; 2Department of Laboratory Medicine, Inje University Ilsan Paik Hospital, Goyang, Korea
Corresponding author: Mi-Na Kim, M.D., Ph.D.
Department of Laboratory Medicine, University of Ulsan College of Medicine and Asan Medical Center, 88 Olympic-ro 43-gil, Songpa-gu, Seoul 05505, Korea
Tel: +82-2-3010-4511 Fax: +82-2-478-0884 E-mail: mnkim@amc.seoul.kr
Received: October 22, 2019; Revised: December 4, 2019; Accepted: February 5, 2020; Published online: July 1, 2020.
© Korean Society for Laboratory Medicine. All rights reserved.

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Abstract
This study investigated resistance mechanisms and epidemiology of emerging linezolid-nonsusceptible Enterococcus faecalis (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 cfr or optrA resistance gene. We used pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing for the molecular typing of the isolates. Among 4,318 E. faecalis isolates, 10 (0.23%) were linezolid-nonsusceptible. All LNSEF isolates were optrA-positive and cfr-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 E. faecalis one month before LNSEF detection. In conclusion, heterogenous clones of optrA-positive LNSEF emerged in the hospital mainly via community-onset.
Keywords: Linezolid resistance, Mechanism, Epidemiology, optrA, Enterococcus faecalis, Pulsed-field gel electrophoresis, Multilocus sequence typing



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