Influence of the method for detecting reduced vancomycin susceptibility in meticillin-resistant Staphylococcus aureus bacteraemia. A 14-year study

Abstract number: P1460

Camarena J.J., Gonzalez R., Nogueira J.M., Zaragoza R., Andrade P., Quintero V.

Objectives: Actually, in clinical cases of methicilin-resistant Staphylococcus aureus infections with low vancomycin susceptibility (MIC > 1 mg/L) (MRSA-LVS) the new drugs are indicated like alternative treatment. The aims of this study were to kwon the prevalence of MRSA-LVS strains in bloodstream infections in our hospital and the influence of the method used in routine diagnosis for detecting reduced vancomycin susceptibility.

Methods: From 1994 to november-2007, 172 patients with a clinically significant MRSA nosocomial or community-adquired bacteraemia were detected in the Microbiology Department of a university hospital. MIC vancomycin determination was performed by automated (VITEK 2 – bioMérieux) and macro E-Test (AB Biodisk) methods. A compared study of the MIC vancomycin obtained by both methods in each year of the period was analised.

Results: During the last 14 years, twenty-one (12.2%) of the MRSA bacteremic infections showed a LVS (MIC > 1 mg/L) with the VITEK-2 results, in front of 84.3% MRSA-LSV (145 cases) detected by E-Test method. MIC of all strains was <4 mg/L with VITEK 2. Fifteen of them (8.7%) showed a MIC leqslant R: less-than-or-eq, slant4 mg/L by E-Test. The analysis by VITEK 2 from different periods of the study display a significant progressive increase of the MRSA-LVS percentage (1994–99: 6.1%; 2000–03: 7.3%; 2004–2005: 12.8%; 2006: 14.8%; and 2007: 25.1%). However, by E-Test the obtained MIC were usually higher since in the 1994–2000 period all MRSA-LVS were MIC 2 mg/L (54.5%) and in 2000–07 period more than 90% showed a MIC leqslant R: less-than-or-eq, slant 2 mg/L. No vancomycin resistant was detected.

Conclusion: Detection in laboratory routine of MRSA with reduced vancomycin susceptibility is depending on the microbiology method used. The automated systems show a progressive increase of the MRSA-LVS bacteremic cases, but is not correlated whit the E-Test MIC results. The method used to detect MRSA-LVS and their prevalence must be interpreted cautiously.

Session Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Location: Barcelona, Spain
Presentation type:
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