Distribution of Corynebacterium Species and Comparative Results of Diagnostic Methods for Identifying Corynebacterium in Experimental Mice in Korea

Simple Summary Experimental mice are the most commonly used laboratory animals for biomedical research and comparative studies. However, microbial infection may alter the mouse phenotype and confound interpretation results. The genus Corynebacterium, Gram-positive diphtheroid rod-shaped bacteria, induces severe diseases, such as hyperkeratosis and pseudotuberculosis, in immunodeficient mice. In this report, we described the population of Corynebacterium spp. isolated from laboratory mice in Korea using different approaches, comparing the accuracy and problems associated with each method. When identified based on molecular methods such as 16S rRNA and rpoB gene sequence analysis, the main Corynebacterium species were C. mastitidis (44.8%), C. bovis (25.5%), C. lowii (21.2%), and C. amycolatum (8.5%). In addition, matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) yielded results that were 77.9% identical to the molecular results, whereas biochemical methods showed only 15.5% identical to molecular identification. Collectively, our findings indicate that the different results may be obtained depending on the method used to identify Corynebacterium isolated from experimental mice, highlighting the importance of selecting an appropriate Corynebacterium identification method in obtaining accurate identification results. This result will help to increase the reliability of Corynebacterium diagnosis result from experimental mice. The genus Corynebacterium, composed of Gram-positive diphtheroid rod-shaped bacteria, induces severe diseases, such as Corynebacterium-associated hyperkeratosis and pseudotuberculosis, in immunodeficient mice. We isolated and identified a total of 165 strains of Corynebacterium species from experimental mice in Korean laboratories, diagnosed using several methods. When identified based on molecular methods, namely, 16S rRNA and rpoB gene sequence analysis, the main Corynebacterium species isolated in Korean laboratory mice were C. mastitidis (44.8%, n = 74), C. bovis (25.5%, n = 42), C. lowii (21.2%, n = 35), and C. amycolatum (8.5%, n = 14). Diagnoses were also performed using matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) and biochemical methods. MALDI-TOF MS yielded results that were 77.9% identical to the molecular identification results, whereas biochemical methods showed only 15.5% identical to molecular identification, partly owing to difficulties in distinguishing among C. mastitidis strains. Collectively, our findings indicate that molecular biological methods are better suited for detecting and identifying Corynebacterium species candidates isolated from mice than biochemical methods. Because of limitations associated with the use of MALDI-TOF MS, more precise results will be obtained by complementing this approach with other methods when used for rapid identification testing.

Automated summary

In this study, Corynebacterium species were isolated and identified from experimental mice in Korean laboratories using various methods. Molecular methods, particularly 16S rRNA and rpoB gene sequence analysis, showed higher accuracy in species identification compared to MALDI-TOF MS and biochemical methods. It is crucial to choose appropriate identification methods to obtain accurate results in diagnosing Corynebacterium in experimental mice.