Emergence and spread of a mupirocin-resistant variant of the European epidemic fusidic acid-resistant impetigo clone of Staphylococcus aureus in Belgium, 2013 to 2023

Abstract

Background Coresistance to both mupirocin and fusidic acid in Staphylococcus aureus affects the treatment of impetigo in Belgium, where they are the only topical treatments available. Aim We investigated resistance to fusidic acid and mupirocin in methicillin-susceptible S. aureus (MSSA) strains involved in community-acquired skin and soft tissue infections (SSTIs). Methods The 10-year variation in fusidic acid and mupirocin resistance in outpatients with SSTI-associated MSSA was studied in two large laboratories. MSSA strains coresistant to fusidic acid and mupirocin and sent to the Belgian Staphylococci Reference Centre were spa-typed and analysed for the presence of the eta and etb virulence genes and the mupA resistance gene. In addition, whole-genome sequencing was performed on isolates collected in the last 2 years. Results Fusidic acid and mupirocin resistance increased over time, and coresistance in children reached 8.9–10.1% in the third quarter 2023. From 2018 to 2023, 64/70 (91.4%) mupirocin-resistant MSSA strains were coresistant to fusidic acid. Whole-genome sequencing revealed that 29/33 (87.9%) of the isolates were sequence type ST121, clonal and more distantly related to the European epidemic fusidic acid-resistant impetigo clone (EEFIC) observed in Belgium in 2020. These strains carried the mupA and fusB genes, which confer resistance to mupirocin and fusidic acid, respectively, and the eta and etb virulence genes. Conclusion We highlight the spread of a mupirocin-resistant EEFIC (M-EEFIC) in children, with a seasonal trend for the third quarter. This is of concern because this variant is resistant to the two main topical antibiotics used to treat impetigo in Belgium.