The emergence of antibiotic resistance in Mycobacterium tuberculosis has been the culprit behind the inefficient treatment of tuberculosis (TB). Mycobacteriophages being rapid and specific in their activity against mycobacteria including M. tuberculosis are an emerging alternative solution to the antibiotic resistance problem. D29 mycobacteriophage is known as an efficient lytic phage. Its lytic cassette encodes for two lytic proteins, Lysin A (LysA) and Lysin B (LysB), and a holin protein responsible for the translocation of the former two. LysB is a mycolyl-arabinogalactan esterase, which has shown a promising lytic effect on M. tuberculosis. In this study, we explored the lytic efficiency of D29 mycobacteriophage LysB protein on drug-resistant strains of M. tuberculosis. We demonstrate that LysB effectively lyses multi-drug-resistant M. tuberculosis both alone and along with anti-TB drugs. We also report that the surfactant Tween-80, although not vital, potentiates LysB activity. We are able to demonstrate that LysB can eliminate M. tuberculosis residing in mouse macrophages. Thus, by combining our in vitro and ex vivo data, we are able to claim that LysB is a potential phage-derived therapeutic which should undergo pre-clinical and clinical trials.

To combat the rapidly emerging drug-resistant M. tuberculosis, it is now essential to look for alternative therapeutics. Mycobacteriophages can be considered as efficient therapeutics due to their natural ability to infect and kill mycobacteria including M. tuberculosis. Here, we have exploited the mycolyl-arabinogalactan esterase property of LysB encoded from mycobacteriophage D29. This study is novel in terms of targeting a multi-drug-resistant pathogenic strain of M. tuberculosis with LysB and also examining the combination of anti-TB drugs and LysB. All the experiments include external administration of LysB. Therefore, the remarkable lytic activity of LysB overcomes the difficulty to enter the complex cell envelope of mycobacteria. Targeting the intracellularly located M. tuberculosis by LysB and non-toxicity to macrophages take the process of the development of LysB as a drug one step ahead, and also, the interaction studies with rifampicin and isoniazid will help to form a new treatment regimen against tuberculosis.