Reliability of the BD GeneOhm Methicillin-Resistant Staphylococcus aureus (MRSA) Assay in Detecting MRSA Isolates with a Variety of Genotypes from the United States and Taiwan

Abstract

ABSTRACT The BD GeneOhm methicillin-resistant Staphylococcus aureus (MRSA) assay is a molecular screening test for detection of MRSA in nasal colonization. This assay coamplifies the extremity of staphylococcal chromosome cassette mec (SCC mec ) and adjacent chromosomal DNA at the SCC mec insertion site. Increasing reports of novel SCC mec types and the diverse genetic backgrounds of MRSA strains prompted us to test the accuracy of the BD GeneOhm MRSA kit with 914 MRSA isolates with a variety of SCC mec types harbored in 21 genetic backgrounds, as determined by the multilocus sequence type (ST). The BD GeneOhm MRSA assay was performed on colony lysates; purified genomic DNA (0.2 pg/μl and 0.2 ng/μl) was tested to confirm negative results from lysates. Of 914 MRSA isolates tested, 911 tested positive (detection rate, 99.7%). The SCC mec types carried by assay-positive isolates were I, II, III, IV, V, V (5C2&5) , VI, and VIII and SCC mec composite islands with mec class A and ccr complexes 2 and 4. One of the assay-negative isolates had a community-associated genotype: ST8, SCC mec type IV. However, this was an outlier among the 99.8% (434/435) ST8, SCC mec type IV-containing isolates that tested positive. The two other assay-negative isolates had a health care-associated genotype (ST5); both carried a distinct, uncommon, composite SCC mec type. In summary, the BD GeneOhm MRSA assay had a high rate of detection of MRSA isolates harboring common and uncommon SCC mec types from the United States and Taiwan.