Knockout of MRA_1916 in Mycobacterium tuberculosis H37Ra affects its growth, biofilm formation, survival in macrophages and in mice

Malate:quinone oxidoreductase knockout makes Mycobacterium tuberculosis susceptible to stress and affects its in vivo survival

Mycobacterium tuberculosis H37Ra (Mtb-Ra) ORF MRA_2875, annotated as malate:quinone oxidoreductase (mqo), is thought to have a role in TCA cycle in converting malate to oxaloacetate. To study its physiological relevance, we developed mqo knockout (KO) in Mtb-Ra. A KO complemented (KOC) strain was also developed by complementing the KO with mqo over-expressing construct. Under normal in vitro conditions, KO does not show any growth defect but showed reduced CFU burden in macrophages and in mice lungs. In vitro studies with KO showed reduced fitness under oxidative and low pH stress, and also increased susceptibility to levofloxacin and D-cycloserine. Transcript analysis of mqo showed increased expression levels under oxidative and low pH stress. This is the first study to show physiological relevance of mqo encoded by MRA_2875 in Mtb-Ra under oxidative and low pH stress. In summary, the present study shows that MRA_2875 encoded malate:quinone oxidoreductase is a functional enzyme which contributes to oxidative stress and low pH tolerance, and survival in macrophages and in mice.

Macrophage targeted iron oxide nanodecoys augment innate immunological and drug killings for more effective Mycobacterium Tuberculosis clearance

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb) infection, is still one of the top killers worldwide among infectious diseases. The escape of Mtb from immunological clearance and the low targeting effects of anti-TB drugs remain the substantial challenges for TB control. Iron is particularly required for Mtb growth but also toxic for Mtb in high dosages, which makes iron an ideal toxic decoy for the 'iron-tropic' Mtb. Here, a macrophage-targeted iron oxide nanoparticles (IONPs)-derived IONPs-PAA-PEG-MAN nanodecoy is designed to augment innate immunological and drug killings against intracellular Mtb. IONPs-PAA-PEG-MAN nanodecoy exhibits preferential uptake in macrophages to significantly increase drug uptake with sustained high drug contents in host cells. Moreover, it can serve as a specific nanodecoy for the 'iron-tropic' Mtb to realize the localization of Mtb contained phagosomes surrounding the drug encapsulated nanodecoys and co-localization of Mtb with the drug encapsulated nanodecoys in lysosomes, where the incorporated rifampicin (Rif) can be readily released under acidic lysosomal condition for enhanced Mtb killing. This drug encapsulated nanodecoy can also polarize Mtb infected macrophages into anti-mycobacterial M1 phenotype and enhance M1 macrophage associated pro-inflammatory cytokine (TNF-α) production to trigger innate immunological responses against Mtb. Collectively, Rif@IONPs-PAA-PEG-MAN nanodecoy can synergistically enhance the killing efficiency of intracellular Mtb in in vitro macrophages and ex vivo monocyte-derived macrophages, and also significantly reduce the mycobacterial burdens in the lung of infected mice with alleviated pathology. These results indicate that Rif@IONPs-PAA-PEG-MAN nanodecoy may have a potential for the development of more effective therapeutic strategy against TB by manipulating augmented innate immunity and drug killings.

Mycobacterium tuberculosis survival and biofilm formation studies: effect of D-amino acids, D-cycloserine and its components

D-amino acids play an important role in cell wall peptidoglycan biosynthesis. Mycobacterium tuberculosis D-amino acid oxidase deletion led to reduced biofilm-forming ability. Other recent studies also suggest that the accumulation of D-amino acids blocks biofilm formation and could also disperse pre-formed biofilm. Biofilms are communities of bacterial cells protected by extracellular matrix and harbor drug-tolerant as well as persistent bacteria. In Mycobacterium tuberculosis, biofilm formation or its inhibition by D-amino acids is yet to be tested. In the present study, we used selected D-amino acids to study their role in the prevention of biofilm formation and also if D-cycloserine's activity was due to presence of D-Serine as a metabolite. It was observed that D-serine limits biofilm formation in Mycobacterium tuberculosis H37Ra (Mtb-Ra), but it shows no effect on pre-formed biofilm. Also, D-cycloserine and its metabolic product, hydroxylamine, individually and in combination, with D-Serine, limit biofilm formation in Mtb-Ra and also disrupts existing biofilm. In summary, we demonstrated that D-alanine, D-valine, D-phenylalanine, D-serine, and D-threonine had no disruptive effect on pre-formed biofilm of Mtb-Ra, either individually or in combination, and D-cycloserine and its metabolite hydroxylamine have potent anti-biofilm activity.