Mammaliicoccus sciuri as a sentinel for antimicrobial resistance and virulence: genomic epidemiology, transmission dynamics, and control in the one health era.

Mammaliicoccus sciuri (M. sciuri), a Gram-positive bacterium belonging to the group of coagulase-negative staphylococci (CoNS), has been taxonomically reclassified from the genus Staphylococcus to the newly established genus Mammaliicoccus. Its adaptability across diverse niches supports its relevance to One Health. Widely distributed in livestock and diverse environments, M. sciuri has been increasingly reported as an opportunistic pathogen and genetic reservoir for antimicrobial resistance (AMR) and virulence determinants of relevance to human and veterinary medicine. This review provides a synthesis of existing literature regarding the epidemiology, ecological niches, clinical relevance of the M. sciuri species, as well as the genomic and genetic features that underpin its contribution to the dissemination of resistance and virulence factors. Furthermore, it examined the global spread of methicillin-resistant M. sciuri (MR-M. sciuri) clones, characterized through phylogenetic analyses, sequence types (STs), and their complex transmission dynamics. The molecular basis of its resistance mechanisms is explored, with attention directed toward the genetic environments surrounding the mecA and mecC genes within the SCCmec cassettes, as well as the involvement of mobile genetic elements and heavy metal resistance systems. The genetic repertoire of M. sciuri, including the presence of CRISPR–Cas systems associated with adaptive immunity and genome plasticity, was also examined. Moreover, the review delves into the duality of M. sciuri as it can produce antimicrobials such as bacteriocins, which are active against bacteria and fungi. Finally, this review outlines control strategies, including genomic surveillance and stricter antimicrobial regulations, to address MDR M. sciuri strains in the human-animal-environment interface.