Molecular Characteristics and Antimicrobial Resistance of Linezolid-Resistant Staphylococcus aureus in Osteoarticular Infections: A 11-Year Study From a Hospital in Xi'an.

Purpose: This study examines the distribution of pathogens and the characteristics of linezolid-resistant Staphylococcus aureus (LRSA) in osteoarticular infections (OAIs) over an 11-year period.

Methods: Identification and initial antimicrobial susceptibility testing were conducted using the VITEK2 compact system. Broth microdilution method (BMD) to confirm linezolid-resistant isolates. The results were interpreted according to the Clinical and Laboratory Standards Institute (CLSI) guideline. Polymerase chain reaction (PCR) screening identified linezolid-resistance-related genes and molecular typing loci.

Results: From 2012 to 2022, 2049 clinical isolates were collected, with S. aureus identified as the leading pathogen, constituting 38.90% (797/2049) of cases. Among the 797 S. aureus isolates, eight strains were initially identified as LRSA through VITEK2; however, only one isolate was confirmed as LRSA by BMD. For the eight strains, molecular typing revealed four spa types (t030, t037, t002, t437) and three MLST types, with ST239-t030 as the dominant clone. No transferable resistance genes (cfr, optrA, poxtA) were detected, but a G2576T mutation, associated with reduced linezolid sensitivity, was identified in two isolates (included the isolate confirmed as LRSA by BMD) subjected to extended linezolid therapy.

Conclusion: Our findings highlight the importance of accurate susceptibility testing and proactive monitoring of LRSA in the treatment of chronic OAIs to mitigate potential therapeutic challenges.