First Report of a Multidrug-Resistant Mammaliicoccus sciuri Strain Harboring exhB Isolated from an Alpaca with an...

Intracranial abscesses are extremely rare in alpacas, and previously reported cases have lacked systematic etiological characterization. The virulence characteristics of Mammaliicoccus sciuri (formerly Staphylococcus sciuri) in alpaca intracranial infections remain unclear. We investigated an alpaca with chronic otitis media and an intracranial abscess. Bacteria were recovered from intracranial purulent material and several other sites. A representative isolate was designated CS234. It was identified as M. sciuri by 16S rDNA sequencing and whole-genome sequencing (WGS). Average nucleotide identity (ANI) analysis showed 95.58% identity with M. sciuri NCTC12103. WGS identified mecA, mecA1, fexA, optrA, and sal(A). The isolate showed phenotypic resistance to aminoglycosides, tetracyclines, and macrolides. PCR screening detected several virulence-associated gene targets, including exhB and tsst-1. To our knowledge, this is the first report of exhB in M. sciuri. In an intraperitoneal mouse challenge, the median lethal dose (LD₅₀) was 4.4 × 10⁷ colony-forming units (CFU)/g body weight. Multiple-organ lesions were also observed. These findings indicate systemic pathogenic potential in mice. Recovery of M. sciuri from several affected sites indicates a strong etiological association with the suppurative disease in this alpaca. These findings expand current knowledge of M. sciuri infection and antimicrobial resistance in alpacas. They may also aid the diagnosis and treatment of similar cases.