Document Type
Article
Publication Date
11-2019
Publication Source
Journal of Clinical Microbiology
Abstract
Molecular diagnostic tests can be used to provide rapid identification of staphylococcal species in blood culture bottles to help improve antimicrobial stewardship. However, alterations in the target nucleic acid sequences of the microorganisms or their antimicrobial resistance genes can lead to false-negative results. We determined the whole-genome sequences of 4 blood culture isolates of Staphylococcus aureus and 2 control organisms to understand the genetic basis of genotypephenotype discrepancies when using the Xpert MRSA/SA BC test (in vitro diagnostic medical device [IVD]). Three methicillin-resistant S. aureus (MRSA) isolates each had a different insertion of a genetic element in the staphylococcal cassette chromosome (SCCmec)-orfX junction region that led to a misclassification as methicillin-susceptible S. aureus (MSSA). One strain contained a deletion in spa, which produced a false S. aureus-negative result. A control strain of S. aureus that harbored an SCCmec element but no mecA (an empty cassette) was correctly called MSSA by the Xpert test. The second control contained an SCCM1 insertion. The updated Xpert MRSA/SA BC test successfully detected both spa and SCCmec variants of MRSA and correctly identified empty-cassette strains of S. aureus as MSSA. Among a sample of 252 MSSA isolates from the United States and Europe, 3.9% contained empty SCCmec cassettes, 1.6% carried SCCM1, <1% had spa deletions, and <1% contained SCCmec variants other than those with SCCM1. These data suggest that genetic variations that may interfere with Xpert MRSA/SA BC test results remain rare. Results for all the isolates were correct when tested with the updated assay.
ISBN/ISSN
Print: 0095-1137; Electronic: 1098-660X
Document Version
Published Version
Copyright
Copyright © 2019 Tenover et al.
Publisher
American Society for Microbiology
Volume
57
Peer Reviewed
yes
Issue
11
Keywords
MRSA, SCCmec, oxacillin resistance, empty cassette
eCommons Citation
Tenover, Fred C.; Tickler, Isabella A.; Le, Victoria M.; Dewell, Scott; Mendes, Rodrigo E.; Goering, Richard V.; and MRSA Consortium, "Updating Molecular Diagnostics for Detecting Methicillin- Susceptible and Methicillin-Resistant Staphylococcus aureus Isolates in Blood Culture Bottles" (2019). Biology Faculty Publications. 344.
https://ecommons.udayton.edu/bio_fac_pub/344
COinS
Comments
The document is made available through the publisher's open-access policy. Permission documentation is on file.
This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International license.