Comparison of Immune Responses between Smooth and Rough Variant of Mycobacterium Mucogenicum

Background Mycobacterium mucogenicum (Mmuc), a rapidly growing nontuberculous mycobacterium (NTM), is a rarely causative agent of clinical diseases such as post-traumatic wound infections and catheter-related sepsis in immunocompromised patients. Especially, Mmuc has been identified as a water contaminant in the hospital because it was more resistant to chlorine than other bacteria including M. fortuitum as well as E. coli. Like other NTM species mycobacteria such as M. abscessus, Mmuc has a characteristic to exhibit colony morphologies of rough (R) and variable smooth (S) types. It is known that R type is associated with more severe and persistent infection than S type. However, little is known about the immune responses of Mmuc. Methods To compare the immune responses between S and R type of Mmuc, S types including ATCC 49650 and two clinical strains, and one clinical strain with R type were obtained from the Korean Mycobacteria Resource Center (KMRC) of Korean Institute of Tuberculosis. Therefore, each type of Mmuc were infected to murine bone marrow-derived macrophage (BMDM), then intra-macrophage growth of Mmuc were measured by time dependently. Lastly, we conducted the ELISA of inflammatory cytokine secretion and then confirmed cell death pattern by FACS analysis. Results Macrophages infected with R strain had the higher numbers of intracellular bacteria after 3 days post-infection than S strains. Also, the R strain induced higher levels of cytokine production such as TNF-α, IL-6 and derived more necrotic cell death of BMDM. Conclusions In Conclusion, these Results suggest that R strain has more virulence and induces stronger immune response than S strains likewise other NTM species, MAC and M. abscessus. It is meaningful as the first finding about differential immune responses of Mmuc, also it might provide a fundamental research for further studies on Mmuc pathogenesis.