Conversion of Mycobacterium smegmatis to a pathogenic phenotype via passage of epithelial cells during macrophage infection

• Published in: Medical microbiology and immunology 2011-08, Vol.200 (3), p.177-191
• Main Authors: Kim, Su-Young, Sohn, Hosung, Choi, Go-Eun, Cho, Sang-Nae, Oh, Taegwon, Kim, Hwa-Jung, Whang, Jake, Kim, Jong-Seok, Byun, Eui-Hong, Kim, Woo Sik, Min, Ki-Nam, Kim, Jin Man, Shin, Sung Jae
• Format: Article
• Language: English
• Subjects: Animals; Bacteria; Bacterial Load; Bacteriology; Bioinformatics; Biological and medical sciences; Biomedical and Life Sciences; Biomedicine; Bronchoalveolar Lavage Fluid - immunology; Cell Line; Computational Biology; Cytokines - analysis; Epithelial Cells - immunology; Epithelial Cells - microbiology; Female; Flow Cytometry; Fundamental and applied biological sciences. Psychology; Gene expression; Gene Expression Regulation, Bacterial; Genes, Bacterial; Genotype & phenotype; Humans; Immunology; L-Lactate Dehydrogenase - analysis; Lung - microbiology; Macrophages - immunology; Macrophages - microbiology; Medical Microbiology; Mice; Mice, Inbred C57BL; Microbiology; Miscellaneous; Mycobacterium Infections, Nontuberculous - immunology; Mycobacterium Infections, Nontuberculous - microbiology; Mycobacterium smegmatis; Mycobacterium smegmatis - genetics; Mycobacterium smegmatis - immunology; Mycobacterium smegmatis - pathogenicity; Original Investigation; Pathogens; Phenotype; Transcriptional Activation; Virology; Virulence
• ISSN: 0300-8584; 1432-1831
• DOI: 10.1007/s00430-011-0190-5

Mycobacteria encounter many different cells during infection within their hosts. Although alveolar epithelial cells play an essential role in host defense as the first cells to be challenged upon contact with mycobacteria, they may contribute to the acquisition of mycobacterial virulence by increasing the expression of virulence or adaptation factors prior to being ingested by macrophages on the side of pathogens. From this aspect, the enhanced virulence of nonpathogenic Mycobacterium smegmatis (MSM) passed through human alveolar A549 epithelial cells (A-MSM) was compared to the direct infection of MSM (D-MSM) in THP-1 macrophages and mouse models. The intracellular growth rate and cytotoxicity of A-MSM were significantly increased in THP-1 macrophages. In addition, compared to D-MSM, A-MSM induced relatively greater interleukin (IL)-1β, IL-6, IL-8, IL-12, TNF-α, MIP-1α, and MCP-1 in THP-1 macrophages. As a next step, a more persistent A-MSM infection was observed in a murine infection model with the development of granulomatous inflammation. Finally, 58 genes induced specifically in A-MSM were partially identified by differential expression using a customized amplification library. These gene expressions were simultaneously maintained in THP-1 infection but no changes were observed in D-MSM. Bioinformatic analysis revealed that these genes are involved mainly in bacterial metabolism including energy production and conversion, carbohydrate, amino acid, and lipid transport, and metabolisms. Conclusively, alveolar epithelial cells promoted the conversion of MSM to the virulent phenotype prior to encountering macrophages by activating the genes required for intracellular survival and presenting its pathogenicity.