CHARACTERISATION OF DRUG INDUCED CELL DEATH IN MYCOBACTERIUM SMEGMATIS

Abstract

The study on Gram- positive and Gram-negative bacteria by Kohanksi et al. (2007) challenged the longstanding notion about antibiotic induced cell death. The authors showed that these bacteria illustrate a common death pathway when exposed to fluoroquinolones, aminoglycosides and ß-lactams. Cell death, they show, is caused by the production of hydroxyl radicals via the fenton reaction. To determine whether the same pathway is triggered in the evolutionary distinct Mycobacteria, studies were conducted with the fast growing workhorse model organism, M.smegmatis. Upon adapting the protocol described in Kohanski (2008), it was found that we could measure hydroxyl radicals in M. smegmatis generated by H2O2. We show that fluoroquinolones produce hydroxyl radicals, and that the quenching of these radicals resulted in increased bacterial survival indicating their involvement in causing cell death. Three other drugs which are used in Tb therapy, isoniazid, kanamycin and ethambutol were also tested. However, none of them significantly induced hydroxyl radicals. These results suggest that, in contrast to other bacteria, mycobacteria harbor hydroxyl radical dependent as well as independent cell death pathways. This study serves as a foundation to further our knowledge about pathways triggering reactive oxygen species and how we could use them to identify new targets for drug discovery. If such a pathway is activated in M. tuberculosis, it might prove to be very useful in our fight against drug resistant tuberculosis.