Linezolid resistance in clinical isolates of Staphylococcus haemolyticus

Abstract number: 1733_385

Calvo J., Cano M., Marín M., Cercenado E., Martinez-Martinez L.

Objectives: To characterise four isolates of linezolid-resistant S. haemolyticus obtained from different patients.

Methods: Identification and preliminary susceptibility testing of organisms were performed with the WalkAway system. Linezolid MICs were determined by reference microdilution and Etest assays, according to CLSI guidelines and manufacturer's instructions, respectively. Detection of the G2576T mutation was performed by PCR amplification and sequencing of the domain V of 23S rRNA gene (Tsiodras et al, Lancet 2001). Clonal relationship of the isolates was examined by PFGE of SmaI macrorestricted genomic fragments.

Results: Four linezolid-resistant S. haemolyticus isolated in pure cultures from blood samples (n = 3) or bile (n = 1) were identified among 17 organisms of this species obtained in our laboratory in the period March-April 2006. All four isolates were from different patients admitted to ICUs of our hospital. Reference MICs of linezolid were 64 mg/L for 3 isolates and 128 for the other one. Etest yielded one twofold dilution lower in all isolates. The G2576T mutation was detected in all four isolates and all of them were homozygous. Similar resistance phenotype (WalkAway) was observed for all 4 isolates, being resistant to oxacillin, teicoplanin, ciprofloxacin, clindamycin, erythromycin, gentamicin, tobramycin, amikacin, rifampin, trimethoprim-sulfamethoxazol and susceptible to vancomycin, tetracycline and quinupristin-dalfopristin. Two closely related PFGE-patterns were observed for the 4 isolates, each one corresponding to two isolates.

Conclusions: We have identified the emergence of multiresistant S. haemolyticus isolates presenting homozygous resistance to linezolid.

Session Details

Date: 31/03/2007
Time: 00:00-00:00
Session name: European Society of Clinical Microbiology and Infectious Diseases
Location: ICC, Munich, Germany
Presentation type:
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