A Common Variant of Staphylococcal Cassette Chromosome mec Type IVa in Isolates from Copenhagen, Denmark, Is Not Detected by the BD GeneOhm Methicillin-Resistant Staphylococcus aureus Assay

Department of Clinical Microbiology, Hvidovre Hospital, Hvidovre, Denmark.
Journal of clinical microbiology (Impact Factor: 3.99). 04/2009; 47(5):1524-7. DOI: 10.1128/JCM.02153-08
Source: PubMed


Rapid tests for detection of methicillin-resistant Staphylococcus aureus (MRSA) carriage are important to limit the transmission of MRSA in the health care setting. We evaluated the performance
of the BD GeneOhm MRSA real-time PCR assay using a diverse collection of MRSA isolates, mainly from Copenhagen, Denmark, but
also including international isolates, e.g., USA100-1100. Pure cultures of 349 MRSA isolates representing variants of staphylococcal
cassette chromosome mec (SCCmec) types I to V and 103 different staphylococcal protein A (spa) types were tested. In addition, 53 methicillin-susceptible Staphylococcus aureus isolates were included as negative controls. Forty-four MRSA isolates were undetectable; of these, 95% harbored SCCmec type IVa, and these included the most-common clone in Copenhagen, spa t024-sequence type 8-IVa. The false-negative MRSA isolates were tested with new primers (analyte-specific reagent [ASR] BD
GeneOhm MRSA assay) supplied by Becton Dickinson (BD). The ASR BD GeneOhm MRSA assay detected 42 of the 44 isolates that were
false negative in the BD GeneOhm MRSA assay. Combining the BD GeneOhm MRSA assay with the ASR BD GeneOhm MRSA assay greatly
improved the results, with only two MRSA isolates being false negative. The BD GeneOhm MRSA assay alone is not adequate for
MRSA detection in Copenhagen, Denmark, as more than one-third of our MRSA isolates would not be detected. We recommend that
the BD GeneOhm MRSA assay be evaluated against the local MRSA diversity before being established as a standard assay, and
due to the constant evolution of SCCmec cassettes, a continuous global surveillance is advisable in order to update the assay as necessary.

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    • "In our previous study [28], we found a negative result of the assay could almost exclude S. aureus colonization, while a positive result should require culture to confirm it. However, Bartels et al [29] reported that some MRSA isolates with specific SCCmec could be missed by the BD GeneOhm StaphSR assay. "
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    ABSTRACT: Health care workers (HCWs) are at the interface between hospitals and communities. The survey for methicillin-resistant Staphylococcus aureus (MRSA) carriage among HCWs has mostly been conducted to investigate outbreaks or endemics. Community-associated MRSA are prevalent among children in Taiwan. We conducted this study to better understand the carriage rate of MRSA among pediatricians in non-outbreak situations in Taiwan,. A total of 220 pediatricians from Taiwan who attended the annual meeting of Taiwan Pediatric Association in April, 2010 were recruited to participate in this study and were sampled from the nares for the detection of MRSA by polymerase chain reaction (PCR) and further by culture. The following molecular analyses were performed, including pulsed-field gel electrophoresis (PFGE), multilocus sequence typing (MLST), typing of staphylococcal cassette chromosome mec (SCCmec) and the presence of Panton-Valentine leukocidin (PVL) genes. MRSA was detected from 15 attendees (6.8%) by PCR. MRSA-colonized attendees had a significantly lower rate (0.041) of working in the medical center, while borderline significantly higher rate of working in the Regional Hospital (p=0.056), than those without MRSA colonization. From those 15 samples, 12 MRSA isolates were identified by culture and molecularly characterized. Three PFGE patterns, two sequence types (ST 59, ST 508), and two SCCmec types (IV and VT) were identified, respectively. Five isolates, including three carrying SCCmec types VT, were PVL-positive. All 12 isolates were susceptible to vancomycin, teicoplanin, linezolid, fusidic acid, trimethoprim/sulfamethoxazole, and doxycyclin, and resistant to penicillin. Around seven percent of pediatricians in Taiwan harbored CA-MRSA in their nares.
    Full-text · Article · Nov 2013 · PLoS ONE
    • "This strain harbours a divergent mecA homologue with a different organization than other SCC elements leading to a false negative result. Another study from Denmark [30] revealed that a specific common SCCmec clone was frequently not detected in a commercial MRSA assay leading to the conclusion that local diversities play an important role in the performance of MRSA assays, as undetectable low prevalence strains could become widespread among S. aureus. In our study, most of the samples which were false negative in the PCR proved to be positive in a second PCR approach using the isolated MRSA cultures. "
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    ABSTRACT: Nose/throat-swabs from 1049 patients were screened for MRSA using CHROMagar MRSA, LightCycler Advanced MRSA, and Detect-Ready MRSA. Results were compared to the CHROMagar MRSA results, which was set as reference system. MRSA was detected in 3.05% of the patients with CHROMagar MRSA. LightCycler MRSA Advanced showed a higher clinical sensitivity (84.38%) than Detect-Ready MRSA (57.69%).The negative predictive values were high for both tests (>98%). The specificity and the positive predictive value were higher for the Detect-Ready MRSA test than for the LightCycler MRSA test (99.59% and 78.95% versus 98.52% and 64.29%). For routine screening LightCycler MRSA Advanced proved to be more efficient in our clinical setting as the clinical sensitivity was much higher than the sensitivity of Detect-Ready MRSA. CHROMagar MRSA detected more MRSA positive samples than both PCR methods, leading to the conclusion that the combination of PCR with cultural screening is still the most reliable way for the detection of MRSA. LightCycler MRSA Advanced was faster and needed less hands-on time. The advantage of Detect-Ready MRSA was the additional identification of methicillin-sensitive S.aureus (here in 34.63% of the samples), an information which can be possibly used for reducing the risk of postoperative infections in surgical patients in future.
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    • "The commercial PCR assay designs in use identify methicillin-resistant S. aureus (MRSA) [20-23], and they do so by targeting a mobile staphylococcal cassette chromosome (SCC) element referred to as SCCmec [24]. This assay design causes false positive rates that significantly impact MRSA screening efficacy [25-27], in particular in geographic regions where MRSA prevalence is low or on the decrease, and it can also cause false negatives [28,29]. We have developed an alternative molecular detection method that targets S. aureus-specific sequences in the thermonuclease (nuc) gene [30,31]. "
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    ABSTRACT: Background The bacterium Staphylococcus aureus constitutes one of the most important causes of nosocomial infections. One out of every three individuals naturally carries S. aureus in their anterior nares, and nasal carriage is associated with a significantly higher infection rate in hospital settings. Nasal carriage can be either persistent or intermittent, and it is the persistent carriers who, as a group, are at the highest risk of infection and who have the highest nasal S. aureus cell counts. Prophylactic decolonization of S. aureus from patients’ noses is known to reduce the incidence of postsurgical infections, and there is a clear rationale for rapid identification of nasal S. aureus carriers among hospital patients. Findings A molecular diagnostic assay was developed which is based on helicase-dependent target amplification and amplicon detection by chip hybridization to a chip surface, producing a visible readout. Nasal swabs from 70 subjects were used to compare the molecular assay against culturing on “CHROMagar Staph aureus” agar plates. The overall relative sensitivity was 89%, and the relative specificity was 94%. The sensitivity rose to 100% when excluding low-count subjects (<100 S. aureus colony-forming units per swab). Conclusions This molecular assay is much faster than direct culture and has sensitivity that is appropriate for identification of high-count (>100 S. aureus colony-forming units per swab) nasal S. aureus carriers who are at greatest risk for nosocomial infections.
    Full-text · Article · Aug 2012 · BMC Research Notes
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