Emergence of a methicillin-resistant Staphylococcus aureus strains with an unusual susceptibility antibiotic pattern in Tunisia.

Typically, methicillin-resistant Staphylococcus aureus (MRSA) strains exhibit concurrent resistance to numerous commonly used antibiotics. Between June and December 2023, five MRSA strains with an unusual antibiotic susceptibility pattern (susceptible to all antibiotics tested, except cefoxitin) were isolated at Charles Nicolle Hospital of Tunis. Isolates were characterized by whole genome sequencing using the Illumina DNA Prep kit. All isolates carried the mecA gene [SCCmec types IVa (2B) (n = 4) and V (n = 1)]. Virulence genes, including leukocidin genes (lukD, lukE), enterotoxin genes (sea, seg, sei, sem, sen, seo, seu), and immune evasion genes (sak, scn). They were identified as ST97/CC97 (n = 2), ST149/CC5 (n = 2), and ST5/CC4 (n = 1). This study highlights the emergence of MRSA clones with an unusual susceptible antibiotic pattern, emphasizing the importance of continued molecular surveillance to monitor both antimicrobial resistance and virulence traits and track the spread of newly introduced clones, thereby improving infection control strategies.