Real-time evaluation of an optimized real-time PCR assay versus Brilliance chromogenic MRSA agar for the detection of meticillin-resistant Staphylococcus aureus from clinical specimens.
A total of 1204 meticillin-resistant Staphylococcus aureus (MRSA) screens (3340 individual swabs) were tested to evaluate a staphylococcal cassette chromosome mec (SCCmec) real-time PCR. In total, 148 (12.3 %) of the screens were MRSA-positive, where 146 (12.1 %) were MRSA-positive by the SCCmec real-time PCR assay. In contrast, 128 (10.6 %) screens were MRSA-positive by culture. One hundred and twenty-six (10.5 %) of the screens were positive by both culture and PCR. Twenty of the 1204 screens (1.66 %) were negative by culture but positive by PCR; these samples were sequenced. In 14 of the cases, a homology search confirmed the sequence as SCCmec, indicating that these samples could be considered true positives. Two of the 1204 (0.2 %) screens were positive by culture and negative by PCR. The mean turnaround time (TAT) for PCR-negative swabs was 6 h 12 min and for PCR-positive swabs was 6 h 48 min. In comparison, for culture-negative swabs the mean TAT was 29 h 30 min and for culture-positive swabs was 69 h. The cost per swab for routine culture was £0.41 (€0.48) and that of the real-time PCR assay was £2.35 (€2.75). This optimized, in-house, inexpensive, real-time PCR test maintained a very high sensitivity and specificity when evaluated under real-time laboratory conditions. The TAT of this real-time PCR assay was substantially lower than that of chromogenic culture. It was also maintained throughout the entire process, which can be taken as an indirect measure of test performance. This study showed that implementation of a molecular test can be achieved with limited resources in a standard microbiology laboratory.
Department of Microbiology, Royal Infirmary of Edinburgh, Edinburgh, UK.
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Danial
Department of Microbiology, Royal Infirmary of Edinburgh, Edinburgh, UK.
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Noel
Department of Microbiology, Royal Infirmary of Edinburgh, Edinburgh, UK.
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Templeton
Department of Microbiology, Royal Infirmary of Edinburgh, Edinburgh, UK.
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Cameron
Department of Microbiology, Royal Infirmary of Edinburgh, Edinburgh, UK.
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Mathewson
Department of Microbiology, Royal Infirmary of Edinburgh, Edinburgh, UK.
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Smith
Department of Microbiology, Basingstoke and North Hampshire Hospital, Basingstoke, UK.|Department of Microbiology, Royal Infirmary of Edinburgh, Edinburgh, UK.
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JA
Cepeda
D000362:Agar; D001431:Bacteriological Techniques / Q000191:economics / Q000379:methods*; D002863:Chromogenic Compounds; D003470:Culture Media / Q000737:chemistry; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D005798:Genes, Bacterial; D006801:Humans; D055624:Methicillin-Resistant Staphylococcus aureus / Q000302:isolation & purification*; D016133:Polymerase Chain Reaction / Q000191:economics / Q000379:methods*; D012680:Sensitivity and Specificity; D017422:Sequence Analysis, DNA; D013203:Staphylococcal Infections / Q000175:diagnosis* / Q000382:microbiology; D013997:Time Factors
D002863:Chromogenic Compounds; D003470:Culture Media; D004269:DNA, Bacterial; D000362:Agar