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Evaluation of a rapid molecular dipstick assay for the direct detection of methicillin-resistant Staphylococcus aureus in clinical specimens

Abstract number: 1732_14

Eigner U., Holfelder M., Wild U., Bender C., Kirstahler M., Turnwald A., Witte W., Weizenegger M., Fahr A.

Objectives: Methicillin-resistant Staphylococcus aureus (MRSA) causes increasing healthcare problems worldwide. Rapid and sensitive screening methods for direct detection of MRSA are essential to limit further spread in the hospital. The purpose of this study was to evaluate the new molecular dipstick assay GenoQuick® MRSA (Hain Lifescience, Nehren, Germany) for the direct and specific detection of MRSA in clinical specimens.

Methods: The analytical specificity of the assay was evaluated by using a subset of 25 MRSA isolates (including SCCmec types I–V); 17 methicillin-susceptible S. aureus (MSSA) and 38 coagulase-negative staphylocococi (CoNS) of different culture collections. The lower detection limit of the assay was determined by serial dilutions of MRSA strains representing SCCmec types I to IV.

The test was evaluated for direct detection of MRSA in clinical swab specimens. MRSA carriage was analysed by both the standard culture methods [Chromagar MRSA (Becton Dickinson, Heidelberg, Germany), Columbia blood agar, trypticase soy broth] and two PCR assays [GenoQuick MRSA and GenoType® MRSA Direct (Hain Lifescience)]. Both PCR assays were performed directly from the swab and after overnight incubation in trypticase soy broth. MRSA isolates were confirmed using a mecA gene and S. aureus specific PCR. Susceptibility testing was performed with an automated system (VITEK 2, bioMérieux, Nürtingen, Germany).

Results: The lower detection limit of 25 CFU was determined with serially diluted MRSA strains. For analytical specificity all MRSA strains representing SCCmec types I to V were tested positive by the assay. The MSSA and CoNS were tested negative, respectively.

Of 187 patient specimens tested for clinical evaluation, 24 were identified MRSA-positive by culture and by both PCR assays. One specimen was positive only by PCR. Among the 163 culture-negative specimens, 162 were negative with both PCR assays.

The GenoQuick assay showed a diagnostic sensitivity of 100%, and a diagnostic specificity of 99.4%, a positive predictive value of 96% and a negative predictive value of 100%. Time-to-result for the direct detection of MRSA from clinial specimens is reduced to 2h 20min with the molecular GenoQuick MRSA dipstick assay (2h 5min for amplification and 15 min for detection).

Conclusions: The GenoQuick MRSA dip stick assay proved to be a rapid, sensitive and specific assay for direct detection of MRSA in clinical swab specimens in 2h 20min.

Session Details

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