Bhaskar Das

Disinfection of Multidrug Resistant Escherichia coli by Solar-Photocatalysis using Fe-doped ZnO Nanoparticles

Spread of antibiotic resistant bacteria through water, is a threat to global public health. Here, we report Fe-doped ZnO nanoparticles (Fe/ZnO NPs) based solar-photocatalytic disinfection (PCD) of multidrug resistant Escherichia coli (MDR E. coli). Fe/ZnO NPs were synthesized by chemical precipitation technique, and when used as photocatalyst for disinfection, proved to be more effective (time for complete disinfection = 90 min) than ZnO (150 min) and TiO2 (180 min). Lipid peroxidation and potassium (K+) ion leakage studies indicated compromisation of bacterial cell membrane and electron microscopy and live-dead staining confirmed the detrimental effects on membrane integrity. Investigations indicated that H2O2 was the key species involved in solar-PCD of MDR E. coli by Fe/ZnO NPs. X-ray diffraction and atomic absorption spectroscopy studies showed that the Fe/ZnO NPs system remained stable during the photocatalytic process. The Fe/ZnO NPs based solar-PCD process proved successful in the disinfection of MDR E. coli in real water samples collected from river, pond and municipal tap. The Fe/ZnO NPs catalyst made from low cost materials and with high efficacy under solar light may have potential for real world applications, to help reduce the spread of resistant bacteria.

Doped ZnO nanoparticles impregnated on Kaolinite (Clay): A reusable nanocomposite for photocatalytic disinfection of multidrug resistant Enterobacter sp. under visible light

Water contamination by multidrug resistant (MDR) enteric bacteria can be considered as the foremost cause of gastrointestinal infections and poses a threat to global public health. Therefore, there is an urgent need to pursue unorthodox techniques with potential of community scale applications for purging of water borne pathogenic bacteria. We communicate visible-light assisted photocatalytic disinfection (PCD) of an enteric MDR bacterium; Enterobacter sp. using Fe-doped ZnO nanoparticles impregnated on Kaolinite (Clay) (ZnO/K). ZnO/K was synthesized by co-precipitation technique and was found to be more effective than Fe-doped ZnO (ZnO) and Kaolinite for PCD process. Analysis from fluorescence microscopy and electron microscopy (FESEM) proposed complete bacterial cell death via PCD due to damage of bacterial cell membrane. Experimental evidences indicated that O2- could be acting as the most significant component in disinfection of MDR Enterobacter sp. in visible-light assisted PCD process in presence of ZnO/K. Considering the experimental data of Resazurin assay, it is proposed that reactive oxygen species (ROS) generated during PCD might have impeded the oxido-reductase enzyme system of the bacteria and hence trammeling its metabolic activity. Crystal structure and particle size of ZnO/K was found to be unaltered during the photocatalytic process indicating its potential for reusability. When ZnO/K was exposed to HCT-116 Human Colorectal Carcinoma cell lines, about 79% cell survivability was noticed. The synthesized material was successful in completely disinfecting the target microorganism in Zebra Fish model, without producing any adverse effects on the Fish itself, further reinforcing its biocompatibility factor. High effectiveness of PCD process using ZnO/K under visible light in disinfecting enteric MDR bacteria, might have promising outcome as an alternative water disinfection technology to prevent the spread of infectious and resistant bacteria without producing any adverse effect on non-specific flora and fauna.

Quorum Quenching and Biofilm Inhibition: Alternative Imminent Strategies to Control the Disease Cholera

Vibrio cholerae, the causative agent of the disease cholera still threatens a large proportion of world’s population and is considered as a top priority enteric pathogen. Role of biofilm in V. cholerae pathogenesis is well established as it provides the bacterium with enhanced transmission ability during epidemics and also enhanced tolerance to antimicrobial agents. The clinical efficacy of many existing antibiotics is being threatened by the emergence of multi-drug resistant V. cholerae. The rapidly increasing number of cholera outbreaks in several developing countries and emergence of multidrug resistant V. cholerae necessitates the development of an alternative strategy rather than the existing antibiotic therapy to control the pathogen. In the present chapter, we discuss the different quorum sensing pathways in V. cholerae, the common quorum quenching molecules that targets these pathways and a novel strategy of biofilm inhibition in V. cholerae using antibiofilm compounds in combination with antibiotics to control the disease. Co-dosing strategy reduce the dosage of antibiotics and such a combination therapy can in turn be used to control the spread of antibiotic resistance.

Strategies Behind Biosensors for Food and Waterborne Pathogens

Slackness in the quality control of food and water consumed by human and other animals has become a significant issue which enhances the possibilities of cross-contamination with harmful pathogenic microbes. Intake of the contaminated food and water are the causes for the over abundance of infectious diseases in both animals and humans, and this has thus emerged as a global health concern. Detection of microbial contamination in food and water has relied on conventional methods which demand intensified pre-enrichment steps followed by laborious biochemical identification techniques. Recently, most promising and advanced techniques in biological sensor development have dragged all the scientist’s attention which primarily deals with rapid real-time sensing applications due to its selectivity, sensitivity and specificity. In this book chapter, the possible routes of pathogenic infections have been outlined along with its various detection mechanisms. Additionally, strategies for the biosensor development have also been elaborated based on their transducing properties.

Biosynthesis of magnesium oxide (MgO) nanoflakes by using leaf extract of Bauhinia purpurea and evaluation of its antibacterial property against Staphylococcus aureus

Nanobiotechnology has become a newly evolving field of interest in biomedical applications due to its biocompatibility and non-toxic nature towards the environment. Metal and metal oxide nanoparticles have been widely used as an antibacterial agent due to the emergence of antibiotic resistant pathogens, which leads to the outbreak of infectious diseases. In the present paper, biogenic synthesis of magnesium oxide (MgO) nanoflakes is reported by using Bauhinia purpurea leaf extract through alkaline precipitation method along with its detailed characterization. The average size of synthesized nanoflakes was found to be around 11 nm. Electron microscopy was used to investigate the morphology of the MgO nanoflakes. Additionally, the presence of antioxidants, phenolics and flavonoids in B. purpurea leaf extract has been studied by using different assays, which suggested the efficacy of leaf extract as a potential reducing agent for MgO nanoflakes synthesis. Antibacterial activity of synthesized MgO nanoflakes was investigated against Staphylococcus aureus, a gram positive bacteria known to cause various infections in humans. Results suggested the high efficacy of MgO nanoflakes as a potential antibacterial agent against S. aureus at meager dose size (250 μg/ml) and possible mode of action was investigated through surface morphology analysis of bacterial cells by field emission scanning electron microscopy.

Study of soy-fortified green tea curd formulated using potential hypocholesterolemic and hypotensive probiotics isolated from locally made curd

Recently there has been an increased demand for functional foods to reduce the risk of cardiovascular diseases mainly related to hypercholesterolemia, because of undesirable side effects of traditional drugs (statins). Hence, in the quest for natural and safer alternatives, this work is aimed to bring together the health-promoting properties of probiotics, soymilk, bovine milk and green tea into one product, i.e., soy-fortified green tea curd (GTC). This study includes isolation and characterization of microbes for probiotic attributes, from locally made curd which could reduce cholesterol and produce angiotensin-converting enzyme inhibitors in vitro. The best isolate was used for the production of soy-fortified GTC, and the effect of refrigerated storage on bacterial viability, tea polyphenol contents, and organoleptic properties was investigated. CI1 (Enterococcus faecium) depicted best probiotic potential amongst the 15 isolates. Soy-fortified GTC depicted higher probiotic viability for a longer duration during refrigerated storage and greater ACEI activity than unfortified GTC.