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Nanoscale materials hold considerable promise in the mitigation of bacterial infections. In order to exploit nanomaterials as delivery systems in an antibacterial therapeutic paradigm, it is critical to ensure that the generated material is nontoxic. Based on the fundamental principle of biomineralization, we herein report the generation of biocompatible hydroxyapatite nanoparticles (HANPs) in the presence of proteins secreted by the lactic acid bacteria (LAB) Lactobacillus plantarum MTCC 1325, Lactobacillus plantarum CRA52, and Pediococcus pentosaceus CRA51. The biogenic HANPs were characterized by AFM, FETEM, powder XRD, DLS, and FTIR analysis. Interestingly, HANPs could also be synthesized using an ∼20 kDa protein purified from the secreted protein extract obtained from L. plantarum MTCC 1325, which suggested that this lower molecular weight protein fraction was perhaps significantly involved in biomineralization-based generation of HANPs. In order to develop a therapeutic bactericidal nanocomposite, HANPs were loaded with the antibiotic polymyxin B (PB). A Langmuir isotherm model was evident in the studies that measured adsorption of PB onto HANPs. A sustained release profile of PB from the nanocomposite was observed in buffers having varying pH and in simulated body fluid. The nanocomposite (PB−HNC) exhibited bactericidal as well as antibiofilm activity against Pseudomonas aeruginosa MTCC 2488 and was nontoxic to cultured human embryonic kidney cells.

The present study highlights the prospect of an anthraquinonebased ligand (C1) as an inhibitor of micrococcal nuclease (MNase) enzyme secreted by Staphylococcus aureus. MNase inhibition rendered by 5.0 μM C1 was ~96 % and the ligand could significantly distort the β-sheet conformation present in MNase. Mechanistic studies revealed that C1 rendered noncompetitive inhibition, reduced the turnover (K cat ) and catalytic efficiency (K m /K cat ) of MNase with an IC 50 value of 323 nM. C1 could also inhibit nuclease present in the cell-free supernatant (CFS) of a methicillin-resistant Staphylococcus aureus (MRSA) strain. A C1-loaded human serum albumin (HSA)-based nanocarrier (C1-HNC) was developed, which was amicable to protease-triggered release of payload in presence of the CFS of an MRSA strain. Eluates from C1-HNC could effectively reduce the rate of MNase-catalyzed DNA cleavage. The non-toxic nature of C1-HNC in conjunction with the non-competitive mode of MNase inhibition rendered by C1 offers interesting therapeutic prospect in alleviation of MRSA infections.