Ann Lab Med.  2019 Jan;39(1):36-42. 10.3343/alm.2019.39.1.36.

Molecular Epidemiology and Mechanisms of 43 Low-Level Linezolid-Resistant Enterococcus faecalis Strains in Chongqing, China

• Hua R
• Xia Y
• Wu W
• Yang M
• Yan J

• KMID: 2420269
• DOI: http://doi.org/10.3343/alm.2019.39.1.36

Abstract

BACKGROUND
Enterococcus faecalis strains with low-level resistance to linezolid (an oxazolidinone antibiotic) have become common. No large-scale study has examined the underlying mechanisms in linezolid-resistant E. faecalis (LRE) strains. We investigated these mechanisms and molecular characteristics in Chongqing, China.
METHODS
A total of 1,120 non-duplicated E. faecalis strains collected from August 2014 to June 2017 underwent drug susceptibility testing. LRE strains were screened for optrA, cfr, and mutations in the 23S rRNA and ribosomal proteins L3 and L4 by PCR amplification and sequencing. Multi-locus sequence typing (MLST) and pulsed-field gel electrophoresis (PFGE) were used for epidemiological analysis.
RESULTS
All 43 low-level LRE strains (minimum inhibitory concentration: 8-16 mg/L) harbored optrA; cfr and 23S rRNA mutations were not detected. Novel mutations in the ribosomal proteins L3 and L4"”one deletion (Q103del) and four substitutions (S113L, T35A, I98V, and N79D)"”were identified. Novel amino acid substitutions at positions E60K, G197D, and T285P of the OptrA protein were observed. MLST revealed 20 types of LRE strains; the most common type was ST16 (32.6%). PFGE showed 14 strains of ST16 with unique banding patterns. Eight novel sequence types (ST823 to ST830) and one allele (gki95) were identified for the first time in China.
CONCLUSIONS
optrA plays an important role in linezolid resistance and may serve as a marker for resistance screening. Since the L3 and L4 mutations did not simultaneously occur in the same strain, they play a negligible role in linezolid resistance. Epidemiological investigation suggested that the LRE cases were sporadic.

Keyword

Linezolid; Resistance; Mechanism; Enterococcus; Epidemiology

MeSH Terms

Alleles
Amino Acid Substitution
China*
Electrophoresis, Gel, Pulsed-Field
Enterococcus faecalis*
Enterococcus*
Epidemiology
Linezolid
Mass Screening
Molecular Epidemiology*
Polymerase Chain Reaction
Ribosomal Proteins
Linezolid
Ribosomal Proteins

Figure

• 

  Fig. 1 Epidemiology analysis of low-level linezolid-resistant Enterococcus faecalis isolates by MLST and PFGE. (A) GoeBURST diagram for the MLST data set of 43 linezolid-resistant E. faecalis isolates. The eBURST diagram was calculated using PHYLOViZ with the goeBURST algorithm; it contains 20 unique STs for a total of 43 isolates in the database. Each circle represents one ST and the size represents the number of strains in each ST. (B) PFGE fingerprinting dendrogram and PFGE pattern of 14 linezolid-resistant ST16 E. faecalis strainsAbbreviations: ST, sequence type; MLST, multi-locus sequence typing; PFGE, pulsed field gel electrophoresis.

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