In blood cultures that test positive for staphylococcal bacteria, rapid identification of methicillin-resistant Staphylococcus aureus (MRSA) or methicillin-susceptible Staphylococcus aureus (MSSA) by molecular assay is useful for appropriate antimicrobial treatment of bloodstream infections. Although the Xpert MRSA/SA BC assay is widely available in clinical settings in Japan, its efficacy has not yet evaluated thoroughly.
We retrospectively studied 100 blood culture cases positive for S. aureus at Sapporo Medical University Hospital between March 2019 and May 2022. Cycle threshold (CT) values for target genes from the Xpert MRSA/SA BC assay were compared to phenotypic results. Genotyping and genetic analysis of the orfX-SCCmec junction region was performed for selected isolates.
We analyzed 25 and 75 isolates assigned to MRSA and MSSA, respectively, using the Xpert MRSA/SA BC assay. Of these, 99 isolates from agar cultures showed compatible susceptibility to oxacillin. One genetically misidentified case of MRSA was found to be caused by the mixed growth of MSSA and methicillin-resistant S. hominis on agar culture. Of the 73 MSSA with pure growth on agar culture, 45 (61.6%) were found to be orfX-SCCmec-positive, spa-positive, and mecA-negative in this assay. These MSSA belong to diverse spa and coa types.
The Xpert MRSA/SA BC assay accurately identified MRSA and MSSA in positive blood cultures. However, over half of the MSSA isolates showed positive results for orfX-SCCmec, presumably due to genetic diversity in the orfX-associated region of MSSA. Therefore, the coexistence of MSSA and mecA-harboring coagulase-negative staphylococci may cause confusion about identification of MRSA.
To read this article in full you will need to make a payment
Purchase one-time access:Academic & Personal: 24 hour online accessCorporate R&D Professionals: 24 hour online access
One-time access price info
- For academic or personal research use, select 'Academic and Personal'
- For corporate R&D use, select 'Corporate R&D Professionals'
Subscribe:Subscribe to Journal of Infection and Chemotherapy
Already a print subscriber? Claim online access
Already an online subscriber? Sign in
Register: Create an account
Institutional Access: Sign in to ScienceDirect
- Japanese association for acute medicine (JAAM) focused outcomes research in emergency care in acute respiratory distress syndrome sepsis and trauma (forecast) study group. Current spectrum of causative pathogens in sepsis: a prospective nationwide cohort study in Japan.Int J Infect Dis. 2021; 103: 343-351https://doi.org/10.1016/j.ijid.2020.11.168
- The JAID/JSC guidelines for management of infectious diseases 2017 – sepsis and catheter-related bloodstream infection.J Infect Chemother. 2021; 27: 657-677https://doi.org/10.1016/j.jiac.2019.11.011
- Diagnosis of bloodstream infections from positive blood cultures and directly from blood samples: recent developments in molecular approaches.Clin Microbiol Infect. 2018; 24: 944-955
- Clinical impact of implementation of rapid diagnostic testing of blood cultures with Staphylococcus aureus on patient outcomes.Diagn Microbiol Infect Dis. 2021; 101115474
- Rapid detection of Staphylococcus aureus and methicillin-resistant S. aureus (MRSA) in wound specimens and blood cultures: multicenter preclinical evaluation of the Cepheid Xpert MRSA/SA skin and soft tissue and blood culture assays.J Clin Microbiol. 2009; 47: 823-826
- Comparison of the next-generation Xpert MRSA/SA BC assay and the GeneOhm StaphSR assay to routine culture for identification of Staphylococcus aureus and methicillin-resistant S. aureus in positive-blood-culture broths.J Clin Microbiol. 2015; 53: 804-809
- Xpert MRSA/SA BC manufacturer's instructions.
- The genotype-to-phenotype dilemma: how should laboratories approach discordant susceptibility results?.J Clin Microbiol. 2021; 59 (20)e00138
- Performance standards for antimicrobial susceptibility testing.30th ed. CLSI, Wayne, Pennsylvania2020
- Combination of multiplex PCRs for staphylococcal cassette chromosome mec type assignment: rapid identification system for mec, ccr, and major differences in junkyard regions.Antimicrob Agents Chemother. 2007; 51: 264-274
- Clonal diversity and genetic characteristics of methicillin-resistant Staphylococcus aureus isolates from a tertiary care hospital in Japan.Microb Drug Resist. 2019; 25: 1164-1175
- Clonal diversity of methicillin-resistant Staphylococcus aureus (MRSA) from bloodstream infections in northern Japan: identification of spermidine N-acetyltransferase gene (speG) in staphylococcal cassette chromosomes (SCCs) associated with type II and IV SCCmec.J Glob Antimicrob Resist. 2021; 24: 207-214
- Clonal diversity and molecular characteristics of methicillin-susceptible and -resistant Staphylococcus aureus from pediatric patients in Myanmar.Microb Drug Resist. 2022;
- New real-time PCR assay for rapid detection of methicillin-resistant Staphylococcus aureus directly from specimens containing a mixture of staphylococci.J Clin Microbiol. 2004; 42: 1875-1884https://doi.org/10.1128/JCM.42.5.1875-1884.2004
- Characterization of Staphylococcus aureus isolates with a partial or complete absence of staphylococcal cassette chromosome elements.J Clin Microbiol. 2010; 48: 3525-3531
- The Japanese clinical practice guidelines for management of sepsis and septic shock 2020 (J-sscg 2020).Acute Med Surg. 2021; 8: e659
- Evaluation of combined use of MALDI-TOF and Xpert(®) MRSA/SA BC assay for the direct detection of methicillin resistance in Staphylococcus aureus from positive blood culture bottles.J Infect. 2013; 67: 91-92
- Does nasal cocolonization by methicillin-resistant coagulase-negative staphylococci and methicillin-susceptible Staphylococcus aureus strains occur frequently enough to represent a risk of false-positive methicillin-resistant S. aureus determinations by molecular methods?.J Clin Microbiol. 2006; 44: 229-231https://doi.org/10.1128/JCM.44.1.229-231.2006
- Multiplex real-time PCR assay for detection of methicillin-resistant Staphylococcus aureus (MRSA) strains suitable in regions of high MRSA endemicity.J Clin Microbiol. 2013; 51: 1008-1013https://doi.org/10.1128/JCM.02495-12
- Evaluation of the BD max StaphSR assay for rapid identification of Staphylococcus aureus and methicillin-resistant S. aureus in positive blood culture broths.J Clin Microbiol. 2015; 53: 3630-3632
- High proportion of wrongly identified methicillin-resistant Staphylococcus aureus carriers by use of a rapid commercial PCR assay due to presence of staphylococcal cassette chromosome element lacking the mecA gene.J Clin Microbiol. 2011; 49: 722-724
- Performance of BD max StaphSR for screening of methicillin-resistant Staphylococcus aureus isolates among a contemporary and diverse collection from 146 institutions located in nine U.S. Census regions: prevalence of mecA dropout mutants.J Clin Microbiol. 2016; 54: 204-207
- Updating molecular diagnostics for detecting methicillin-susceptible and methicillin-resistant Staphylococcus aureus isolates in blood culture bottles.J Clin Microbiol. 2019; 57 (19)e01195
- Detection and characterisation of SCCmec remnants in multiresistant methicillin-susceptible Staphylococcus aureus causing a clonal outbreak in a Swedish county.Eur J Clin Microbiol Infect Dis. 2012; 31: 141-147
Published online: May 20, 2023
Accepted: May 2, 2023
Received in revised form: April 23, 2023
Received: March 1, 2023
Publication stageIn Press Corrected Proof
© 2023 Japanese Society of Chemotherapy and The Japanese Association for Infectious Diseases. Published by Elsevier Ltd. All rights reserved.