Dataset Information

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

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.

SUBMITTER: Hua R

PROVIDER: S-EPMC6143467 | biostudies-literature | 2019 Jan

REPOSITORIES: biostudies-literature

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Molecular Epidemiology and Mechanisms of 43 Low-Level Linezolid-Resistant <i>Enterococcus faecalis</i> Strains in Chongqing, China.

Hua Ruoyi R Xia Yun Y Wu Wenyao W Yang Mi M Yan Jia J

Annals of laboratory medicine 20190101 1

<h4>Background</h4><i>Enterococcus faecalis</i> 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 <i>E. faecalis</i> (LRE) strains. We investigated these mechanisms and molecular characteristics in Chongqing, China.<h4>Methods</h4>A total of 1,120 non-duplicated <i>E. faecalis</i> strains collected from August 2014 to June 2017 underwent drug susceptibility testing. L ...[more]

PMID: 30215228

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Project description:We studied the clinical isolates Enterococcus faecium NEF1, resistant to high levels of vancomycin (MIC, 512 microg/ml) and teicoplanin (MIC, 64 microg/ml); Enterococcus faecium BM4653 and BM4656 and Enterococcus avium BM4655, resistant to moderate levels of vancomycin (MIC, 32 microg/ml) and to low levels of teicoplanin (MIC, 4 microg/ml); and Enterococcus faecalis BM4654, moderately resistant to vancomycin (MIC, 16 microg/ml) but susceptible to teicoplanin (MIC, 0.5 microg/ml). The strains were distinct, were constitutively resistant via the synthesis of peptidoglycan precursors ending in D-alanyl-D-lactate, and harbored a chromosomal vanD gene cluster that was not transferable. New mutations were found in conserved domains of VanS(D): at T(170)I near the phosphorylation site in NEF1, at V(67)A at the membrane surface in BM4653, at G(340)S in the G2 ATP-binding domain in BM4655, in the F domain in BM4656 (a 6-bp insertion), and in the G1 and G2 domains of BM4654 (three mutations). The mutations resulted in constitutivity, presumably through the loss of the phosphatase activity of the sensor. The chromosomal Ddl D-Ala:D-Ala ligase had an IS19 copy in NEF1, a mutation in the serine (S(185)F) or near the arginine (T(289)P) involved in D-Ala1 binding in BM4653 or BM4655, respectively, and a mutation next to the lysine (P(180)S) involved in D-Ala2 binding in BM4654, leading to the production of an impaired enzyme. In BM4653 vanY(D), a new insertion sequence, ISEfa9, belonging to the IS3 family, resulted in the absence of D,D-carboxypeptidase activity. Strain BM4656 had a functional D-Ala:D-Ala ligase, associated with high levels of both VanX(D) and VanY(D) activities, and is the first example of a VanD-type strain with a functional Ddl enzyme. Study of these five clinical isolates, displaying various assortments of mutations, confirms that all VanD-type strains isolated so far have undergone mutations in the vanS(D) or vanR(D) gene, leading to constitutive resistance, but that the Ddl host ligase is not always impaired. Based on sequence differences, the vanD gene clusters could be assigned to two subtypes: vanD-1 and vanD-4.

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Dataset Information

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

Publications

Molecular Epidemiology and Mechanisms of 43 Low-Level Linezolid-Resistant <i>Enterococcus faecalis</i> Strains in Chongqing, China.

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