Can M. smegmatis be used as a real alternative for M. tuberculosis

Background: The structome analysis of M. tuberculosis (MTB) has been performed and reported. The aim of this study was to compare the data obtained from M. smegmatis (MSG) structome analysis with those of MTB and to validate its availability as a real alternative of MTB. Methods: MSG type strain was cultured with Middlebrook 7H9 broth. Cells were processed through rapid freeze-substitution and the serial ultrathin sections of two cells were examined with transmission electron microscopy (TEM). Whole-mount ice-embedded MTB and MSG cells were examined with cryoTEM. Results: Based on the structome analysis, MSG cell diameter, length, cytoplasmic volume and total ribosome number on average were 0.59 µm, 5.88 µm, 1.05 fl, and 8,940, respectively. The diameter and total ribosome number were significantly higher than those of MTB (p Discussion and Conclusion: Although MSG is often used as an alternative for MTB in experimental tuberculosis because it grows faster in the lower biosafety level facility than MTB, MSG cells were different from MTB cells in several phenotypes including total cytoplasmic ribosome number. It is suggested that MSG is not adequate to an alternative of MTB to investigate mechanisms of tuberculosis. Reference: PLoSONE 10:e0117109, 2015.