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

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.

Detection of nucleic acid sequence-based amplification products by gold nanoprobe-based solution hybridization for the diagnosis of invasive aspergillosis / 临床检验杂志

Objective To establish a method of gold nanoprobe-based solution hybridization (GNBSH) to detect nucleic acid sequence-based amplification (NASBA) products for the rapid diagnosis of invasive aspergillosis (IA).Methods The Aspergillus specific 18S rRNA was amplified by NASBA and then the amplified products were hybridized with the gold nanoprobes which were modified with thiol compounds at the 5'end.Serum samples from 106 patients,including 14 with a definite IA,32 with suspected IA and 60 without IA,were detected by the established method,and the obtained results were compared with that of galactomannan (GM) test to evaluate its accuracy.Results The gold nanoprobes only hybridized with Aspergillus NASBA products but not other non-Aspergillus strains.The sensitivity,specificity and the area under the ROC curve (AUCROC) of the established GNBSH method for detecting 106 clinical samples were 82.61％ (38/46),81.67％ (49/60) and 0.890,respectively.The sensitivity,specificity and AUCROC of GM test were 56.52％ (26/46),83.33％ (50/60) and 0.723,respectively.Conclusion The established GNBSH method to detect Aspergillus NASBA products has high sensitivity and specificity and simple operation,which may be used to detect the infection of Aspergillus by clinical laboratories.