Phenotypic and genotypic characterisation of linezolid-resistant coagulase-negative staphylococci possessing cfr-carrying plasmid

Objectives: Linezolid-dependent growth has contributed to wide dissemination of Staphylococcus epider-midis in hospitals. This study aimed to characterise linezolid-resistant coagulase-negative staphylococci (CoNS) isolates and the possibility of linezolid dependence in China. Methods: Phenotypic and genotypic resistance of 13 CoNS isolates were investigated by antimicrobial susceptibility testing and PCR. Similarity of isolates was determined by pulsed-field gel electrophoresis (PFGE). Characterisation of the cfr-carrying plasmid was performed by S1 nuclease PFGE, Southern blot-ting and whole-genome sequencing (WGS). A maximum likelihood phylogenetic tree was constructed for phylogenetic analysis. Growth curve analysis was performed with and without linezolid to determinate the possible contribution of linezolid dependence to linezolid-resistant CoNS dissemination. Results: Thirteen CoNS isolates showed linezolid MICs of 8 mg/L to > 256 mg/L, typed into three PFGE profiles. Southern blotting and WGS indicated that the cfr gene was located on a 39.5-kb plasmid with 99% identity to cfr-harbouring plasmids pSR01, pLRSA417 and pH29-46. The cfr gene was flanked by two copies of an IS256-like element ISEnfa4 family transposase, indicating the transferability of linezolid re-sistance conferred by the cfr gene. Comparative phylogenetic analysis revealed that Staphylococcus capitis XZ03 shared high similarity with linezolid-resistant S. capitis isolates in Huashan Hospital, Shanghai. Thir-teen CoNS isolates did not exhibit linezolid dependence on exposure from 8-32 mg/L. Conclusion: The endemic CoNS clone carrying the cfr gene in our hospital showed high-level linezolid resistance, threatening linezolid use. Linezolid-dependent growth under linezolid selective pressure was not observed, indicating that it may not yet be a common phenotype in Staphylococcus spp.(c) 2022 The Author(s). Published by Elsevier Ltd on behalf of International Society for Antimicrobial Chemotherapy. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ )

Automated summary

This study characterized linezolid-resistant coagulase-negative staphylococci (CoNS) isolates in China and assessed the possibility of linezolid dependence. The results showed high-level linezolid resistance in CoNS isolates, but no linezolid-dependent growth was observed under linezolid selective pressure. These findings are important for understanding and controlling the dissemination of CoNS.