Involvement of CorA of Mycobacterium smegmatis in exerting intrinsic resistance towards structurally unrelated antibiotics.

Aim: Ubiquitous magnesium transporter, CorA of Mycobacterium smegmatis is well known for its role in maintaining magnesium homeostasis. However, little is known about its involvement in exerting antimicrobial resistance. Here, by using molecular genetics, in vivo and in silico studies, we tried to envisage the role of CorA of M. smegmatis in antimicrobial resistance of M. smegmatis and Escherichia coli.

Methods and results: Expression of corA in M. smegmatis and E. coli decreased the susceptibility of the host cells towards various antibiotics and anti-tubercular drugs, which was elucidated by determining minimum inhibitory concentrations using the micro-broth dilution method. The intracellular antibiotic accumulation assay indicated that the host cells expressing corA accumulated less EtBr, norfloxacin, and ofloxacin than the control cells. Moreover, the presence of a sub-inhibitory concentration of Mg2+ further decreased the susceptibility towards the drugs tested. Furthermore, CorA enhanced the biofilm-forming ability of cells expressing it.

Conclusion: CorA (MSMEG_5056), a magnesium transporter of M. smegmatis influences the extrusion of multiple structurally unrelated classes of drugs and enhances the biofilm formation of E. coli and M. smegmatis.