A Clinical Scoring Systems for the Evaluation of Corynebacterium bovis -associated Disease in NSG Mice

Clinical signs of Corynebacterium bovis infections are well-known in athymic nude mice. However, C. bovis can also infect and cause clinical signs in many hirsute, immunocompromised mouse strains such as NSG (NOD. Cg-Prkdc^scid Il2rg^tm1Wgl/SzJ). Typically, the clinical assessment of C. bovis-infected mice begins when overt clinical signs are initially observed and thus the early course of infection has not been thoroughly described. The goal of this study was to characterize the clinical progression of C. bovis infection in NSG mice under experimental conditions and develop a quantifiable clinical scoring system. For the development and application of this clinical scoring system, 54 naïve NSG mice were exposed to soiled bedding from clinically ill C. bovis-infected NSG mice and the emergence of clinical signs was monitored and scored weekly for 8 wk. Overall, we identified 6 benchmark changes associated with C. bovis clinical infection. Four changes were the appearance of the eyes, ears, hair coat, and posture. Two behavioral changes were increased grooming activity and rapid head shaking. All clinical signs appeared consistently and progressed temporally with increasing clinical severity. Characterization of clinical signs and scoring of clinical disease will aid veterinarians in the assessment of C. bovis-infected NSG mice and may help in the evaluation of current and future clinical interventions used to prevent or treat C. bovis-infected immunodeficient mice.

Detection and Elimination of Corynebacterium bovis from Barrier Rooms by Using an Environmental Sampling Surveillance Program

Rodent health-monitoring programs based on sampling an IVC system's exhaust air dust (EAD) has enhanced and even replaced traditional sentinels for some rodent pathogens. EAD testing by qPCR assay is an optimal surveillance method for the rapid detection of Corynebacterium bovis-infected immunodeficient mice. Here we demonstrate that an active EAD surveillance program for C. bovis can be used to maintain nude mice C. bovis-free after the transition from historically enzootically infected colonies. During 3 events over 3 y, rapid detection of infection, elimination of infected mice, aggressive quarantine measures, and local decontamination prevented the spread of C. bovis within 2 barrier rooms. In total, 4 cages of infected nude mice were identified and removed, preventing the spread of infection to 469 other cages of immunodeficient mice. In addition, we present data regarding a refinement to EAD testing which enables row-specific surveillance of an IVC rack. This technique systemically decreases the amount of testing required to locate an individually infected cage. Due to our ability to rapidly detect and localize an infected cage, we were able to investigate the route of C. bovis introduction into our barrier rooms. Our epidemiologic investigation suggested that the transmission of C. bovis occurred through contaminated, cryopreserved, patient-derived xenograft tumor tissue. This previously unknown source of C. bovis can infect mice used to propagate these tumors. Together, these data demonstrate that a remediation program that combines rapid detection, test-and-cull, and local decontamination under quarantine conditions can eliminate C. bovis from a mouse colony.

Procedure for Horizontal Transfer of Patient-Derived Xenograft Tumors to Eliminate Corynebacterium bovis

Human patient-derived xenograft (PDX) tumors, propagated in immunodeficient mice, are rapidly growing in use as a model for cancer research. Horizontal transfer between mice, without in vitro cell culture, allows these tumors to retain many of their unique characteristics from their individual patient of origin. However, the immunodeficient mouse strains used to grow these tumors are susceptible to numerous opportunistic pathogens, including Corynebacterium bovis. At our institution, 2 in vivo tumor banks of PDX tumors had been maintained within nude mouse colonies enzootically infected with C. bovis. Elimination of C. bovis from these colonies required the aseptic harvest and horizontal transfer of tumor tissue between infected and naïve recipient mice without cross-contamination. Out of necessity, we developed a standard operating procedure using enhancements to traditional aseptic surgical technique with concurrent application of both procedural and physical barriers to prevent C. bovis transmission. By using these methods, all 61 unique PDX tumor models were successfully harvested from C. bovis-infected mice and transferred into recipient mice without transmission of infection. Our data demonstrate that, in situations where C. bovis-free colonies can be established and maintained, this procedure can successfully be used to eliminate C. bovis from an in vivo tumor bank of valuable PDX tumors.

Pathogenicity and genetic variation of 3 strains of Corynebacterium bovis in immunodeficient mice

Corynebacterium bovis has been associated with hyperkeratotic dermatitis and acanthosis in mice. We studied 3 different strains of C. bovis: one previously described to cause hyperkeratotic dermatitis (HAC), one that infected athymic nude mice without leading to the classic clinical signs, and one of bovine origin (ATCC 7715). The 3 strains showed a few biochemical and genetic differences. Immunodeficient nude mice were housed in 3 independent isolators and inoculated with pure cultures of the 3 strains. We studied the transmission of these C. bovis studies to isolator-bedding and contact sentinels housed for 5 to 12 wk in filter-top or wire-top cages in the respective isolators. Using a 16S rRNA-based qPCR assay, we did not find consistent differences in growth and transmission among the 3 C. bovis strains, and neither the incidence nor severity of hyperkeratosis or acanthosis differed between strains. Housing in filter-top compared with wire-top cages did not alter the morbidity associated with any of the strains. Our findings confirmed the variability in the gross and histologic changes associated with C. bovis infection of mice. Although bacteriology was a sensitive method for the detection of Corynebacterium spp., standard algorithms occasionally misidentified C. bovis and several related species. Our study demonstrates that PCR of skin swabs or feces is a sensitive and specific method for the detection of C. bovis infection in mice. An rpoB-based screen of samples from North American vivaria revealed that HAC is the predominant C. bovis strain in laboratory mice.