Molecular characterization of mupirocin-resistant MRSA from Germany and South Africa.

INTRODUCTION: Methicillin-resistant Staphylococcus aureus (MRSA) is a human pathogen of global public health importance. A key element of MRSA decolonization strategies is the administration of mupirocin, an antibiotic also used to treat superficial skin infections. However, the emergence and global increase of mupirocin-resistant (mupR)-MRSA highlight the need for active surveillance to support evidence-based MRSA control measures. This study investigated the antibiotic resistance, genetic diversity, and plasmid profiles of mupR-MRSA from Germany and South Africa.

METHODS: Phenotypic identification of mupR-MRSA strains was verified by molecular methods. Characterization of all strains included PCR detection of Panton-Valentine leucocidin, immune evasion cluster genes, and staphylococcal protein A typing. Representative strains from each spa type were selected for whole-genome sequencing to determine their clonal lineages and relationships, including antibiotic and virulence gene content. Comparative analysis, phylogeny and classification of mupA-carrying plasmids were determined.

RESULTS: Eighty-two mupR-MRSA were characterized, comprising 32 strains that exhibited high-level mupirocin resistance (HmupR) and 50 strains with low-level mupirocin resistance (LmupR). The plasmid-mediated mupA gene and the V588F mutation in the bacterial isoleucyl-tRNA synthetase gene were identified in strains that demonstrated HmupR and LmupR, respectively. However, mupA and the V588F mutation were detected in two strains from Germany. The mupR-MRSA from Germany were assigned to CC1, CC5, CC8, CC22, CC30, and ST59, while those from South Africa were grouped into CC8, CC22, and CC30. The strains harboured different SCCmec types (IIa, III, IVa, IVj, and V). Notably, mupR CC22-MRSA-IVj and tst-positive CC30-MRSA-IIa strains were identified in both countries. The mupA-positive plasmids formed four distinct communities, including two singletons. The mupA-positive plasmids from the strains in Germany often carried the aminoglycoside (aac(6')-Ie/aph(2'')-Ia) resistance genes. However, the β-lactam (blaZ), arsenic (arsB, arsC, arsR), and copper (mco) resistance genes were primarily identified on mupA-positive plasmids from strains obtained in South Africa.

DISCUSSION: This study highlights the genetic diversity and potential for horizontal gene transfer among mupA-positive MRSA lineages in the two countries, further supported by the regional clustering of mupA plasmids. Integrating genomic surveillance of chromosomal- and plasmid-mediated resistance with antimicrobial use and clinical data is needed for targeted MRSA infection prevention and control.