Einsatz einer Single-locus-MRSA-PCR zum Aufnahmescreening auf Methicillin-resistente Staphylococcus aureus (MRSA)
Single-locus-PCR-assays as rapid screening-tests for methicillin-resistant Staphylococcus aureus (MRSA) can provide results within one hour whereas culture may need up to three days. Rapid assays neither detect the mecA-gene nor all variants of SCCmec-types, thus differences between the results of culture and PCR have to be expected. The results of the Cepheid Xpert MRSA PCR were compared with the results of culture of 3079 screening swabs of the years 2009 and 2010 from our hospital. Results: 20 PCR results were false negative, 70 swabs showed a false positive PCR result. Most of the latter grew a methicillin-sensitive Staphylococcus aureus (MSSA). Further examination of these MSSA-isolates by the Cepheid Xpert MRSA SSTI-PCR revealed that they contained a SCCmec-orfX-sequence but not the mecA-gene. 8 isolates with this so-called mecA-deletion were typed using pulsed field gel electrophoresis (PFGE). Two of these showed an identical PFGE-pattern whereas the others were classified as individual strains. The sensitivity, specificity, negative and positive predictive value of the rapid PCR assay was 93.6 %, 97.5 %, 99.3 % and 80.7 % respectively. Discussion: The retrospective data obtained from daily routine diagnostics in our hospital were comparable to the results of published prospective studies. Because of the high negative predictive value patients with a negative PCR-result did not have to be isolated. However, the high number of false positive PCR results caused additional isolations of patients who turned out not to be carriers of MRSA. It is crucial to perform culture in order to either confirm or correct the PCR result. Culture is indispensable also for the survey of the epidemiology of strains. A change to SCCmec-types not detectable by PCR might cause a lot of false negative results and even nosocomial outbreaks as a consequence. On the other hand the number of false positive results may rise if strains with mecA-deletion become widely distributed.
Subject HeadingsMRSA [GND]
Methicillin-resistant staphylococcus aureus [MeSH]
Polymerase chain reaction [MeSH]