Effects of antibiotics on strains of Mycobacterium smegmatis

Mycobacterium smegmatis is a non-pathogenic microorganism and is classified as an acid-fast bacterium due to the accumulation of mycolic acid outside of its cell wall. Mycobacteria can survive harsh conditions and treatment with antibiotics due to their complex cell envelope. In this research, the effect of antibiotics on Mycobacterium smegmatis mc²155 and Mycobacterium smegmatis Xeno were investigated. The latter of these two is a strain of bacteria infected with the temperate N cluster mycobacteriophage Xeno. The Kirby-Bauer antibiotic sensitivity test was used to examine if the two strains are differentially susceptible to antibiotics. Prior work done in our laboratory showed that M. smegmatis mc²155 infected with various mycobacteriophage were more or less resistant to certain antibiotics. Our results show that, although there was a difference in the diameters of the zones of inhibition obtained for kanamycin, novobiocin, and penicillin, between the two strains, there was no difference when using isoniazid. A combination of isoniazid and any of the aforementioned antibiotics did not show that the drugs can act synergistically. Future studies include the use of DPH anisotropy and laurdan fluorescence test to investigate changes in membrane physical properties when M. smegmatis is cultured in the presence of antibiotics. Also, other members of the lab are attempting to create stable lysogens using the phage Juice456 (F1 subcluster) and Patt (K4 subcluster), which will be used to examine for differential antibiotic susceptibility.