Background: Antimicrobial resistance in Staphylococcus aureus imposes a high disease burden. Both phenotypic and genotypic monitoring are key to understanding and containing emerging resistant strains.
Aim: Phenotypic monitoring of emerging resistance in S. aureus and correlation of priority strain phenotypes with whole-genome sequencing (WGS) findings.
Methods: Antimicrobial susceptibility test results of >40,000 isolates from 213 participating hospitals from 2011 to 2019 were exported from the national Japan Nosocomial Infections Surveillance (JANIS) database. Longitudinal and geographic distribution and prevalence of distinct multi-drug resistance phenotypes ('resistance profiles') of S. aureus were examined among hospitals and prefectures. We further conducted a genome sequence analysis of strains with specific resistance profiles of concern.
Findings: The overall prevalence of meticillin-resistant S. aureus (MRSA) decreased from 40.3% to 35.1% from 2011 to 2019. However, among dozens of S. aureus resistance profiles, only one profile of a type of MRSA, exhibited a statistically significant increase in inpatient frequency, exceeding 10% during the nine years. This MRSA profile showed resistance to oxacillin, erythromycin and levofloxacin. Analysis of WGS results of S. aureus isolates with this phenotype revealed that most belonged to clonal complex 8, and all carried SCCmec IV, typical of community-acquired MRSA.
Conclusion: Tracking distinct resistance profiles deepened our understanding of the overall decrease in MRSA and led to recognition of the emergence of a new resistance phenotype. This study provides a model for future epidemiological research on antimicrobial resistance correlating multi-drug resistance phenotypes with selective genome sequencing, which can be applied to other bacterial species.
Keywords: AMR surveillance; MRSA; Multi-drug phenotype; Staphylococcus aureus; Whole-genome sequencing.
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