Akshay Datey

Dual role of arginine metabolism in establishing pathogenesis.

Arginine is an integral part of host defense when invading pathogens are encountered. The arginine metabolite nitric oxide (NO) confers antimicrobial properties, whereas the metabolite ornithine is utilized for polyamine synthesis. Polyamines are crucial to tissue repair and anti-inflammatory responses. iNOS/arginase balance can determine Th1/Th2 response. Furthermore, the host arginine pool and its metabolites are utilized as energy sources by various pathogens. Apart from its role as an immune modulator, recent studies have also highlighted the therapeutic effects of arginine. This article sheds light upon the roles of arginine metabolism during pathological conditions and its therapeutic potential.

Successful treatment of biofilm infections using shock waves combined with antibiotic therapy.

Many bacteria secrete a highly hydrated framework of extracellular polymer matrix on suitable substrates and embed within the matrix to form a biofilm. Bacterial biofilms are observed on many medical devices, endocarditis, periodontitis and lung infections in cystic fibrosis patients. Bacteria in biofilm are protected from antibiotics and >1,000 times of the minimum inhibitory concentration may be required to treat biofilm infections. Here, we demonstrated that shock waves could be used to remove Salmonella, Pseudomonas and Staphylococcus biofilms in urinary catheters. The studies were extended to a Pseudomonas chronic pneumonia lung infection and Staphylococcus skin suture infection model in mice. The biofilm infections in mice, treated with shock waves became susceptible to antibiotics, unlike untreated biofilms. Mice exposed to shock waves responded to ciprofloxacin treatment, while ciprofloxacin alone was ineffective in treating the infection. These results demonstrate for the first time that, shock waves, combined with antibiotic treatment can be used to treat biofilm infection on medical devices as well as in situ infections.

Chronic lung infection by Pseudomonas aeruginosa biofilm is cured by L-Methionine in combination with antibiotic therapy

Bacterial biofilms are associated with 80–90% of infections. Within the biofilm, bacteria are refractile to antibiotics, requiring concentrations >1,000 times the minimum inhibitory concentration. Proteins, carbohydrates and DNA are the major components of biofilm matrix. Pseudomonas aeruginosa (PA) biofilms, which are majorly associated with chronic lung infection, contain extracellular DNA (eDNA) as a major component. Herein, we report for the first time that L-Methionine (L-Met) at 0.5 μM inhibits Pseudomonas aeruginosa (PA) biofilm formation and disassembles established PA biofilm by inducing DNase expression. Four DNase genes (sbcB, endA, eddB and recJ) were highly up-regulated upon L-Met treatment along with increased DNase activity in the culture supernatant. Since eDNA plays a major role in establishing and maintaining the PA biofilm, DNase activity is effective in disrupting the biofilm. Upon treatment with L-Met, the otherwise recalcitrant PA biofilm now shows susceptibility to ciprofloxacin. This was reflected in vivo, in the murine chronic PA lung infection model. Mice treated with L-Met responded better to antibiotic treatment, leading to enhanced survival as compared to mice treated with ciprofloxacin alone. These results clearly demonstrate that L-Met can be used along with antibiotic as an effective therapeutic against chronic PA biofilm infection.

Mesoporous silica–chondroitin sulphate hybrid nanoparticles for targeted and bio-responsive drug delivery

This work proposes the fabrication of a novel targeted drug delivery system based on mesoporous silica-biopolymer hybrids that can release drugs in response to biological stimuli present in cancer cells. The proposed system utilizes mesoporous silica nanoparticles as a carrier to host the drug molecules. A bio-polymer cap is attached onto these particles which serves the multiple functions of drug retention, targeting and bio-responsive drug release. The biopolymer chondroitin sulphate used here is a glycosaminoglycan that can specifically bind to receptors over-expressed in cancer cells. This molecule also possesses the property of disintegrating upon exposure to enzymes over-expressed in cancer cells. When these particles interact with cancer cells, the chondroitin sulphate present on the surface recognizes and attaches onto the CD44 receptors facilitating the uptake of these particles. The phagocytised particles are then exposed to the degradative enzymes, such as hyaluronidase present inside the cancer cells, which degrade the cap resulting in drug release. By utilizing a cervical cancer cell line we have demonstrated the targetability and intracellular delivery of hydrophobic drugs encapsulated in these particles. It was observed that the system was capable of enhancing the anticancer activity of the hydrophobic drug curcumin. Overall, we believe that this system might prove to be a valuable candidate for targeted and bioresponsive drug delivery.

Heterogeneity in pneumolysin expression governs the fate of Streptococcus pneumoniae during blood-brain barrier trafficking

Outcome of host-pathogen encounter is determined by the complex interplay between protective bacterial and host defense strategies. This complexity further amplifies with the existence of cell-to-cell phenotypic heterogeneity in pathogens which remains largely unexplored. In this study, we illustrated that heterogeneous expression of pneumolysin (Ply), a pore-forming toxin of the meningeal pathogen, S. pneumoniae (SPN) gives rise to stochastically different bacterial subpopulations with variable fate during passage across blood-brain barrier (BBB). We demonstrate that Ply mediated damage to pneumococcus containing vacuolar (PCV) membrane leads to recruitment of cytosolic “eat-me” signals, galectin-8 and ubiquitin, targeting SPN for autophagic clearance. However, a majority of high Ply producing subset extensively damages autophagosomes leading to pneumococcal escape into cytosol and efficient clearance by host ubiquitination machinery. Interestingly, a low Ply producing subset halts autophagosomal maturation and evades all intracellular defense mechanisms, promoting its prolonged survival and successful transcytosis across BBB, both in vitro and in vivo. Ply therefore acts as both, sword and shield implying that its smart regulation ensures optimal disease manifestation. Our elucidation of heterogeneity in Ply expression leading to disparate infection outcomes attempts to resolve the dubious role of Ply in pneumococcal pathogenesis.

Mechanism of transformation in Mycobacteria using a novel shockwave assisted technique driven by in-situ generated oxyhydrogen

We present a novel method for shockwave-assisted bacterial transformation using a miniature oxyhydrogen detonation-driven shock tube. We have obtained transformation efficiencies of about 1.28 × 106, 1.7 × 106, 5 × 106, 1 × 105, 1 × 105 and 2 × 105 transformants/µg of DNA for Escherichia coli, Salmonella Typhimurum, Pseudomonas aeruginosa, Mycobacterium smegmatis, Mycobacterium tuberculosis (Mtb) and Helicobacter pylori respectively using this method which are significantly higher than those obtained using conventional methods. Mtb is the most difficult bacteria to be transformed and hence their genetic modification is hampered due to their poor transformation efficiency. Experimental results show that longer steady time duration of the shockwave results in higher transformation efficiencies. Measurements of Young’s modulus and rigidity of cell wall give a good understanding of the transformation mechanism and these results have been validated computationally. We describe the development of a novel shockwave device for efficient bacterial transformation in complex bacteria along with experimental evidence for understanding the transformation mechanism.

Corrigendum: Successful treatment of biofilm infections using shock waves combined with antibiotic therapy

This corrects the article DOI: 10.1038/srep17440.

Enhancing the efficiency of desensitizing agents with shockwave treatment – a new paradigm in dentinal hypersensitivity management

Dentine sensitivity, characterised by a sharp dental pain is experienced by the population globally. Desensitizing toothpastes are prescribed to treat dentine hypersensitivity. These agents occlude the exposed dentine tubules thereby reducing fluid movement although the effect is not long lived. We have developed a novel system which uses micro-shockwaves in combination with commercially available desensitizing toothpastes to efficiently treat hypersensitivity. This method of treating hypersensitivity strongly blocks dentinal tubules making it resistant to erosion even by acid challenge. We, thus, report a novel method to manage hypersensitivity using the most minimally invasive technique which is potentially translatable to clinics.

Micro-shock Wave Assisted Plant Transformation

Genetically modified (GM) crops are developed by transforming the desired DNA to plant. There are various methods employed to achieve the required transformation in plants. Agrobacterium mediated transformation and Biolistics or particle bombardment method are the most commonly used methods.