Of Commensals and Opportunists: Genomics of Coagulase‐Negative Staphylococci During Sequential Ear and Eye Infections in a Healthy Adult

Coagulase-negative staphylococci (CoNS) are ubiquitous skin commensals but can cause opportunistic infections and may serve as reservoirs for mobile genetic elements such as the staphylococcal cassette chromosome mec (SCCmec) associated with healthcare-adapted lineages. In this longitudinal, single-participant case study, we characterized CoNS isolates obtained over time from a healthy 32-year-old male who experienced two infection episodes 6 months apart (left ear, followed by the left eye), together with post-recovery sampling from additional body sites. Six CoNS isolates were recovered, tested for antimicrobial susceptibility and subjected to whole-genome sequencing. Genome-based identification showed that the ear and arm isolates were Staphylococcus capitis (subsp. urealyticus and subsp. capitis), whereas three isolates from the symptomatic left eye were Staphylococcus epidermidis. The three S. capitis isolates belonged to distinct sequence types (ST1, ST2, and ST10), while the three S. epidermidis isolates shared a novel sequence type, ST1284. A non-typable, mosaic SCCmec type IV element homologous to SCCmec IVa/IVn was identified in the multidrug-resistant S. capitis subsp. urealyticus ST1 isolate E_e2, recovered from the infected ear. Core-genome phylogeny and genomic signatures placed E_e2 within the proto-NRCS-A clade, indicating that a lineage closely related to hospital-associated outbreak strains can be encountered in a community-dwelling individual without known prior healthcare exposure. These findings provide a within-host genomic snapshot of CoNS dynamics across contiguous anatomical sites, and while the study does not establish causality for infection or permit population-level inference, it highlights the need for broader, systematic community surveillance of CoNS lineages and their mobile genetic elements.