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(a) Antibiotics are reported to enter the cells through porin channels such as Msp family porins .(b) Zn2+ (green dots) imported into the cells through probable Zn2+ importers such as ZIP transporters. (c) Zinc inside the cells may influence the efflux of antibiotics by a co-transportation process through Rv3270 triggered by ATP hydrolysis. (d) Rv3270 possibly captures beta-lactams and extrudes them out of the cells via hypothetical linking proteins (outer membrane efflux adaptor proteins) and porins (Msp family) like AcrAB-TolC and Rv0194. This maintains a lower concentration of the antibiotic inside the cell, reducing its chances of exerting inhibitory effects on cell wall synthesis.
Metal homeostasis is maintained by the uptake, storage and efflux of metal ions that are necessary for the survival of the bacterium. Homeostasis is mostly regulated by a group of transporters categorized as ABC transporters and P-type ATPases. On the other hand, efflux pumps often play a role in drug–metal cross-resistance. Here, with the help of antibiotic sensitivity, antibiotic/dye accumulation and semi-quantitative biofilm formation assessments we report the ability of Rv3270, a P-type ATPase known for its role in combating Mn2+ and Zn2+ metal ion toxicity in Mycobacterium tuberculosis, in influencing the extrusion of multiple structurally unrelated drugs and enhancing the biofilm formation of Escherichia coli and Mycobacterium smegmatis. Overexpression of Rv3270 increased the tolerance of host cells to norfloxacin, ofloxacin, sparfloxacin, ampicillin, oxacillin, amikacin and isoniazid. A significantly lower accumulation of norfloxacin, ethidium bromide, bocillin FL and levofloxacin in cells harbouring Rv3270 as compared to host cells indicated its role in enhancing efflux activity. Although over-expression of Rv3270 did not alter the susceptibility levels of levofloxacin, rifampicin and apramycin, the presence of a sub-inhibitory concentration of Zn2+ resulted in low-level tolerance towards these drugs. Of note, the expression of Rv3270 enhanced the biofilm-forming ability of the host cells strengthening its role in antimicrobial resistance. Therefore, the study indicated that the over-expression of Rv3270 enhances the drug efflux activity of the micro-organism where zinc might facilitate drug–metal cross-resistance for some antibiotics.