Edgar Velez

Impact of MscR Promoter Mutation on MZA Resistance in Mycobacterium Bovis

Morphazinamide (MZA) is an antitubercular drug whose effectiveness against Mycobacteria is attributed to its intracellular breakdown into the first-line drug pyrazinamide, morpholine, and formaldehyde. A recently isolated mutant strain of BCG, a naturally PZA-resistant version of Mycobacterium bovis, acquired a mutation in the mscR promoter region that confers increased resistance to MZA. This mscR gene is responsible for encoding a formaldehyde dehydrogenase that is known to help detoxify formaldehyde. This research uses RT-qPCR to quantify the amount of mscR gene expression that is present in this spontaneous mutant. Minimum inhibitory concentration (MIC) tests were also conducted for both the wild-type (WT) and mutant BCG strain to evaluate the difference in MZA susceptibility due to the promoter mutation. It was found that the mutant BCG strains had greatly increased mscR gene expression compared to that of the WT strain. MIC90 tests showed that the mutant strain had increased resistance to MZA and required a higher MIC90 concentration. This research concluded that the mscR promoter mutation led to upregulated gene expression that increased MZA resistance, and thus formaldehyde resistance, due to the increase of dehydrogenase enzyme activity. Further studies may aim to knockout the mscR gene in BCG to observe its effects on MZA resistance. Additionally, ΔmscR BCG that grow in the presence of MZA may allow for the observation of spontaneous mutants which can then be sequenced to analyze any gene mutations that conferred MZA resistance.