Microbiome-Dependent Protection Against Corynebacterium bovis -Associated Hyperkeratosis in Nude Mice ( Mus musculus...

Corynebacterium bovis , the cause of Corynebacterium -associated hyperkeratosis (CAH), is an important pathogen in immunocompromised mice that is difficult to eliminate and can confound research outcomes. We recently observed that CAH severity varies among outbred athymic nude mouse stocks, but the relative contributions of host genetics and the microbiome remain unclear. We hypothesized that disease course and severity vary based on host genetic stock and/or microbiome composition. Three nude mouse stocks were rederived into the axenic state and either monoinfected with a pathogenic C. bovis isolate (10 ⁴ ; CFU) or given sterile media (n=6/group). Axenic mice were also reassociated with their source microbiome or microbiomes from three other stocks with known differences in CAH severity, then inoculated with C. bovis (n=6) or sterile media (n=2). In a separate experiment, one axenic stock was used to assess the role of C. amycolatum via monoinfection, monoinfection followed by C. bovis challenge, or addition to a nonprotective microbiome followed by C. bovis challenge. Mice were monitored daily for 21 days and scored for skin lesions (0-5). C. bovis monoinfected mice developed disease comparable in severity and timing to conventionally raised controls. Notably, reassociation with Vendor A2's microbiome prevented clinical lesions and reduced histopathologic changes across all stocks. While C. amycolatum as a monoinfection did not cause disease nor reduce disease severity following C. bovis challenge, it delayed the onset and lowered peak scores when added to a non-protective microbiome. These findings demonstrate that C. bovis can cause CAH as a monoinfection, that both host genetics and microbiome composition influence disease progression, and, together with prior work, support its role as the etiologic agent consistent with Koch's postulates. Identifying protective microbiome constituents may inform strategies to reduce disease burden in susceptible mice.