Antimicrobial and mosquitocidal activity of microbial synthesized silver nanoparticles.

Microbial synthesis of nanoparticles is a green approach that interconnects nanotechnology and microbial biotechnology. Here, we synthesized the silver nanoparticles (AgNPs) using bacterial strains of Listeria monocytogenes, Bacillus subtilius and Streptomyces anulatus. We tested the efficacy of AgNPs against the larvae, pupae and adults of Anopheles stephensi and Culex quinquefasciatus. We have also investigated the antifungal activity of AgNPs against the soil keratinophilic fungus of Chrysosporium keratinophilum. The efficacy tests were then performed at different concentrations and varying numbers of hours by probit analysis. The results were obtained using a UV-visible spectrophotometer, and the images were recorded with a transmission electron microscope (TEM). The synthesized AgNPs were in varied shape and sizes. The larvae and pupae of Cx. quinquefasciatus were found highly susceptible to AgNPs synthesized using the L. monocytogenes, B. subtilius and S. anulatus than the An. stephensi, while the adults of An. stephensi were found more susceptible to the AgNPs synthesized using the L. monocytogenes, B. subtilius and S. anulatus the Cx. quinquefasciatus. Further, these nanoparticles have also been tested as antifungal activity against the entomopathogenic fungus C. keratinophilum. The higher zone of inhibition occurred at the concentration level of 50 µl. This study gives an innovative approach to develop eco-friendly AgNPs which act as an effective antifungal agent/fungicide and insecticide.

Silver nanoparticles: a possibility for malarial and filarial vector control technology.

Green synthesis technology is one of the rapid, reliable and best routes for the synthesis of silver nanoparticles (AgNPs). There are bioactive compounds with enormous potential in Azadirachta indica (Neem). The extraordinary mosquitoes warrant nanotechnology to integrate with novel molecules. This will be sustainable technology for future. Here, we synthesized AgNPs using aqueous extracts of leaves and bark of Az. indica (Neem). We tested AgNPs as larvicides, pupicides and adulticides against the malaria vector Anopheles stephensi and filariasis vector Culex quinquefasciatus. The results were obtained using UV-visible spectrophotometer and the images were recorded with a transmission electron microscope (TEM). The efficacy tests were then performed at different concentrations varying many hours by probit analysis. The synthesized AgNPs were spherical in shape and with varied sizes (10.47-nm leaf and 19.22-nm bark). The larvae, pupae and adults of filariasis vector C. quinquefasciatus were found to be more susceptible to our AgNPs than the malaria vector An. stephensi. The first and the second instar larvae of C. quinquefasciatus show a mortality rate of 100% after 30 min of exposure. The results against the pupa of C. quinquefasciatus were recorded as LC50 4 ppm, LC90 11 ppm and LC99 13 ppm after 3 h of exposure. In the case of adult mosquitoes, LC50 1.06 µL/cm(2), LC90 2.13 µL/cm(2) and LC99 2.4 µL/cm(2) were obtained after 4 h of exposure. These results suggest that our AgNPs are environment-friendly for controlling malarial and filarial vectors.

Green nanoparticles for mosquito control.

Here, we have used the green method for synthesis of silver and gold nanoparticles. In the present study the silver (Ag) and gold (Au) nanoparticles (NPs) were synthesized by using the aqueous bark extract of Indian spice dalchini (Cinnamomum zeylanicum) (C. zyelanicum or C. verum J. Presl). Additionally, we have used these synthesized nanoparticles for mosquito control. The larvicidal activity has been tested against the malaria vector Anopheles stephensi and filariasis vector Culex quinquefasciatus. The results were obtained using UV-visible spectrophotometer and the images were recorded with a transmission electron microscope (TEM). The efficacy tests were then performed at different concentrations and varying numbers of hours by probit analysis. The synthesized AgNPs were in spherical shape and average sizes (11.77 nm AgNPs and 46.48 nm AuNPs). The larvae of An. stephensi were found highly susceptible to the synthesized AgNPs and AuNPs than the Cx. quinquefasciatus. These results suggest that the C. zeylanicum synthesized silver and gold nanoparticles have the potential to be used as an ideal ecofriendly approach for the control of mosquito.

Efficacy of fungus mediated silver and gold nanoparticles against Aedes aegypti larvae.

Chrysosporium tropicum is a pathogenic fungus. It is known to be an effective mosquito control agent. In the present study, we have synthesized the silver and gold nanoparticles using C. tropicum. These nanoparticles have been characterized through Microscan reader, X-ray diffractometer, transmission electron microscopy, and further confirmed by scanning electron microscopy. The characterization study confirmed the spherical shape and size (2-15 and 20-50 nm) of gold and silver nanoparticles. These silver and gold nanoparticles have been tested as a larvicide against the Aedes aegypti larvae. The larvicidal efficacy was noted when performed against all instars of A. aegypti at six different log concentrations, and significant results could be observed. The gold nanoparticles used as an efficacy enhancer have shown mortality at three times higher concentration than the silver nanoparticles. The larval mortality was observed after different time of exposures. The mortality values were obtained using the probit analysis. The larvae of A. aegypti were found to be highly susceptible for the silver nanoparticles. The second instar larvae have shown 100% mortality against the silver nanoparticles after 1 h, whereas the first, third, and fourth instars have shown efficacy (LC(50) = 3.47, 4, and 2; LC(90) = 12.30, 8.91, and 4; LC(99) = 13.18, 13.18, and 7.58, respectively) after 1 h. The results could suggest that the use of fungus C. tropicum, silver, and gold nanoparticles is a rapid, environmentally safer, and greener approach for mosquito control. This could lead us to a new possibility in vector control strategy.

Fungal-mediated nano silver: an effective adulticide against mosquito.

Fungi as such are known to be an effective mosquito control agent. In the present investigation, the effect of silver nanoparticles synthesized with Chrysosporium keratinophilum, Verticillium lecanii, and Fusarium oxysporum f.sp. pisi has been evaluated against the adult mosquito of filariasis vector Culex quinquefasciatus. The silver nanoparticles were characterized by using the UV-Vis spectrophotometer and X-ray diffraction techniques. The micrographs of silver nanoparticles were obtained by transmission electron microscope and scanning electron microscope. Elemental analysis on single particle was carried out by EDX analysis. The characterization study confirmed different shapes and sizes of silver nanoparticles. The efficacy test was performed at five different concentrations for a period of 24 h by the probit analysis. The C. quinquefasciatus has shown higher efficacy against the silver nanoparticles synthesized with C. keratinophilum and V. lecanii (lethal concentration (LC)(50) 0.19 and 0.4 µl/cm(2); LC(90) 2.4 and 3.2 µl/cm(2); and LC(99) 4.0 and 5.6 µl/cm(2)) after 22 h of exposure. While the silver nanoparticles synthesized with F. oxysporum f.sp. pisi were found to be less effective against the C. quinquefasciatus, the silver nanoparticles synthesized by C. keratinophilum and V. lecanii were found to be more effective than those generated with the help of F. oxysporum f.sp. pisi and C. quinquefasciatus. The use of fungus-mediated silver nanoparticles is a rapid, environmentally safer, and greener approach for vector control strategy and is adaptable globally.

Genomic characterization and epidemiology of an emerging SARS-CoV-2 variant in Delhi, India.

Delhi, the national capital of India, experienced multiple severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) outbreaks in 2020 and reached population seropositivity of >50% by 2021. During April 2021, the city became overwhelmed by COVID-19 cases and fatalities, as a new variant, B.1.617.2 (Delta), replaced B.1.1.7 (Alpha). A Bayesian model explains the growth advantage of Delta through a combination of increased transmissibility and reduced sensitivity to immune responses generated against earlier variants (median estimates: 1.5-fold greater transmissibility and 20% reduction in sensitivity). Seropositivity of an employee and family cohort increased from 42% to 87.5% between March and July 2021, with 27% reinfections, as judged by increased antibody concentration after a previous decline. The likely high transmissibility and partial evasion of immunity by the Delta variant contributed to an overwhelming surge in Delhi.

Effect of Chrysosporium keratinophilum metabolites against Culex quinquefasciatus after chromatographic purification.

Chrysosporium keratinophilum is known to be a keratinophilic fungus and an effective mosquito control agent. This fungus was grown on Sabauraud dextrose broth in the laboratory at 25°C, while the relative humidity was maintained at 75 ± 5% for 15 days. Filtration process of metabolites was done using whatman-1 filter paper, column chromatography and flash, chromatography. Larvicidal efficacy was performed against all instars of Culex quinquefasciatus. Larvicidal efficacy was performed at six different concentrations with different effective ratios (ethanol/metabolites: 9:1, 8:2, 7:3, 6:4, 5:5, 4:6, 3:7, 2:8, and 1:9). The mortality values were then subjected by the probit analysis. The larval mortalities were observed for a period of 24, 48, and 72 h, respectively. The first and second instars were highly susceptible to 2:8 ratio. In the first instar after column chromatography, LC(50) =26.66 ppm, LC(90) =121.96 ppm, LC(99) =231.86 ppm were observed after 72 h, while after flash chromatography the LC(50) =20 ppm, LC(90) =123.02 ppm, LC(99) =281.83 ppm were observed after 48 h. In the second instar after column chromatography, LC(50) =18.19 ppm, LC(90) =102.32 ppm, LC(99) =162.18 ppm were observed after 72 h, while doing flash chromatography 100% mortality could be recorded after 24 h. In the third instar after column chromatography, the LC(50) =38.01 ppm, LC(90) =131.82 ppm, LC(99) =245.47 ppm were observed after 72 h, while after flash chromatography the LC(50) =17.78 ppm, LC(90) =100 ppm, LC(99) =151.35 ppm. In the fourth instar, LC(50) =61.65 ppm, LC(90) =181.97 ppm, LC(99) =436.51 ppm, while after flash chromatography LC(50) =40 ppm, LC(90) =120 ppm, and LC(99) =223.87 ppm were observed after 72 h. The extracellular metabolites of C. keratinophilum could be a fungal based larvicides resource for the control of C. quinquefasciatus larvae. This could be another agent for biotechnological exploitation, if found suitable in field trials.

Pathogenicity of Fusarium oxysporum against the larvae of Culex quinquefasciatus (Say) and Anopheles stephensi (Liston) in laboratory.

The entomopathogenic fungi Fusarium oxysporum are the next generation mosquito controlling agent. F. oxysporum basically contains unique toxin and can be a selectively good agent in tropical countries. We are reporting here the efficacy of the metabolites of F. oxysporum against the larvae of Anopheles stephensi and Culex quinquefasciatus in the laboratory. F. oxysporum was grown on Czapek Dox broth. The bioassays were run at five different concentrations (1.30, 1.60, 1.77, 1.90, and 2.00 ppm). The LC(50), LC(90), and LC(99) values with 95% fiducial limits and probit equations were calculated by probit analysis. The mortality was observed after 24, 48, and 72 h against all instars. The LC(90) values in the case of C. quinquefasciatus after 48 h when calculated were 1.85, 1.92, 1.87, and 1.87 ppm, respectively, while LC(99) values calculated were 2.24, 2.25, 2.18, and 2.19 ppm. Moreover, after 48 h in the case of A. stephensi, the LC(50) values for the first, second, third, and fourth instars were recorded as 1.48, 1.51, 1.71, and 1.50 ppm, respectively. The LC(90) values recorded were 1.88, 1.91, 1.93, and 1.89 ppm and LC(99) values observed were 2.36, 2.23, 2.26, and 2.21 ppm. The results obtained 24, 48, and 72 h have been compared and it was observed significantly that 48 h after exposure the metabolite has more pathogenicity. The results of the metabolites of F. oxysporum may be considered as a new bio-control agent for vector mosquitoes if the field trial succeeds.

Larvicidal and antibacterial activity of aqueous leaf extract of Peepal (Ficus religiosa) synthesized nanoparticles.

In this study, the zinc oxide nanoparticles (ZnO NPs) and titanium dioxide nanoparticles (TiO2 NPs) were synthesized using the aqueous leaf extract of Ficus religiosa (Peepal tree). The synthesized nanoparticles were tested as larvicides against the larvae of Anopheles stephensi. Further, the synthesized nanoparticles were tested as antibacterial agents against the Escherichia coli (gram negative) and Staphylococcus aureus (gram positive) bacteria. The synthesized nanoparticles were characterized with UV-visible spectroscopy, X-rays powder diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX). The larvicidal mortality was observed after 24 h and 48 h by probit analysis. The antibacterial activity was evaluated using the well diffusion method. The synthesized nanoparticles were irregular shape and varied size. The larvae of An. stephensi were found highly susceptible against the ZnO NPs than the TiO2 NPs and aqueous leaves extract. The highest mortality was observed in synthesized ZnO NPs against first to third instars of (LC50 50, 75, and 5 ppm) and 100% mortality in fourth instars of An. stephensi. The higher zone of inhibition was occurred against the E. coli. This report of present investigation revealed that the rapid biological synthesis of ZnO NPs and TiO2 NPs using aqueous leaf extract of F. religiosa would be effective potential larvicides for mosquito control as well as antimicrobial agents with eco-friendly approach.