Resistance to antibiotics in coagulase-negative staphylococci in an infectious diseases hospital, Iasi, Romania

Abstract number: 1734_34

Dorneanu O., Miftode E., Vremera T., Filip O., Nastasa E., Luca V.

Objectives: 1. To evaluate the resistance of coagulase-negative staphylococci (CoNS) with clinical significance, isolated in the Infectious Diseases Hospital, Iasi, Romania. 2. To assess minimum inhibitory concentration (MIC) of CoNS to oxacillin and vancomycin. 3. To evaluate the accuracy of ATB STAPH 5 (bioMérieux, France) strips in detection of susceptibility of CoNS to oxacillin and vancomycin.

Methods: We have investigated 98 CoNS strains isolated from blood cultures (38 strains), catheters (8 strains), cerebro-spinal fluid (4 strains), pus (8 strains) and urine (40 strains), between 1.01.2004 and 1.11.2006. Clinical significance was supported by presence of prosthetic and indwelling devices, immunocompromised patients' status, isolation of the strain in pure culture from the clinical specimen and the repeated isolation of the same strain over the course of infection. Identification to species level was performed using ID 32 STAPH (bioMérieux, France) strips and susceptibility testing with ATB STAPH 5 (bioMérieux, France). MICs to oxacillin and vancomycin were detected using E test (AB Biodisk, Sweden).

Results: The most frequently encountered CoNS species were S. epidermidis (51.3%) and S. haemolyticus (33.3%). The overall resistance to oxacillin was high, 63.2% (55% in S. epidermidis and 76.9% in S. haemolyticus). Methicillin-resistant CoNS (60 strains) were also resistant to fluoroquinolones (60%), gentamicin (60%), erythromycin (63.3%), tetracycline (60%). For S. epidermidis MIC50 of oxacillin was 0.5 mg/mL and MIC90 was 256 mg/mL. For S. haemolyticus MIC50 of oxacillin was 2 mg/mL and MIC90 was >256 mg/mL. We have also detected 2 CoNS strains with modified susceptibility to vancomycin (4 mg/mL). There were 10 disagreements between the susceptibility testing to oxacillin by ATB STAPH 5 strips and E test, thus the accuracy of the commercial method is 89.7%. None of the 2 strains with modified susceptibility to vancomycin was correctly identified by ATB STAPH 5.

Conclusions: Resistance to antibiotics, especially to oxacillin represents a problem in the management of CoNS infections. Vancomycin and quinupristin-dalfopristin remain excellent alternatives for the therapy of severe infections produced by methicillin-resistant CoNS strains. Accuracy of ATB STAPH 5 (bioMérieux, France) strips is only satisfactory for the detection of oxacillin resistance.

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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