In vitro activity of contezolid and other comparators against clinical Staphylococcus and Enterococcus: a multicenter study in China.

OBJECTIVE

To evaluate the in vitro activity of contezolid against clinical Staphylococcus and Enterococcus isolates from across China, and compare its performance with linezolid and other key agents.

METHODS

A total of 2510 non-duplicate Gram-positive cocci isolates were collected from 70 hospitals in seven Chinese regions. Minimum inhibitory concentrations (MICs) were determined using broth microdilution (BMD) per CLSI guidelines. MIC50/90 values, susceptibility rates, cumulative MIC curves and MIC distribution agreement between contezolid and linezolid were assessed. Linezolid-resistant isolates and contezolid-resistant isolates-defined as those based on CLSI 2025 linezolid breakpoints-underwent whole-genome sequencing and comprehensive screening for known oxazolidinone resistance determinants, including acquired resistance genes, 23S rRNA mutations and amino acid substitutions in ribosomal proteins L3, L4 and L22.

RESULTS

Contezolid exhibited potent in vitro activity, with >99% of isolates inhibited at ≤4 mg/L and showed lower MIC50/90 than linezolid, with a consistently left-shifted cumulative MIC distribution. Cohen's kappa analysis supporting enhanced activity of contezolid. Notably, we report for the first time clinical isolates with contezolid MICs up to 16 mg/L. Whole-genome analysis of 14 linezolid-resistant isolates (including five resistant to contezolid) revealed universal presence of optrA, cfr, fexA and other resistance genes, alongside domain V 23S rRNA mutations and substitutions in ribosomal proteins L3 and L4, supporting a shared genetic basis and potential cross-resistance between the two agents.

CONCLUSIONS

Contezolid demonstrated potent and consistent activity against drug-resistant Gram-positive cocci, supporting its potential as a therapeutic alternative to linezolid. Further studies are needed to confirm resistance mechanisms and clinical utility.