Antimicrobial activity of fluorescent Ag nanoparticles.

UNLABELLED: The antimicrobial activity of fluorescent Ag nanoparticles of 1·5 nm (nAg-Fs) is demonstrated and compared with the other Ag nanoparticles of different shapes and size. The antimicrobial activity was evaluated using Gram-positive (Staphylococcus epidermidis NCIM2493 and Bacillus megaterium) and Gram-negative bacteria (Pseudomonas aeruginosa ATCC27853 and Escherichia coli) and fungal strains (Candida albicans and Aspergillus niger). Insights into the possible mechanism were investigated using fluorescence microscope and cytoplasmic materials release assay. The fluorescence microscopic measurements show that the nAg-Fs are localized at the centre of the cell, and 50% decrease in the fluorescence intensity was observed upon 2-h incubation. Maximum cytoplasmic release was observed with spherical Ag nanoparticles of 10 nm. Although the nAg-F shows minimum cytoplasmic release, it has the highest activity. The microbial killing effect of nAg-Fs is actually originates from its intracellular activity. The antimicrobial activity of nAg-Fs is significantly higher than the other synthesized nanoparticles of different shapes and size. The activity of the nanoparticles has been rationalized by considering the shape, size and surface structure of the particles. SIGNIFICANCE AND IMPACT OF THE STUDY: This study aims to demonstrate the size and shape-dependent antimicrobial activity of Ag nanoparticles. It is shown for the first time that the fluorescent Ag nanoparticles of 1·5 nm have superior antimicrobial activity with respect to the larger particles. The shape and size of the particles actually control their activity. The smaller particles can easily penetrate the cell wall and have pronounced activity. These findings may be useful in the development of potential antimicrobial agents.

Novel route of tannic acid biotransformation and their effect on major biopolymer synthesis in Azotobacter sp. SSB81.

AIMS: To examine tannic acid (TA) utilization capacity by nitrogen-fixing bacteria, Azotobacter sp. SSB81, and identify the intermediate products during biotransformation. Another aim of this work is to investigate the effects of TA on major biopolymers like extracellular polysaccharide (EPS) and polyhydroxybutyrate (PHB) synthesis. METHODS AND RESULTS: Tannic acid utilization and tolerance capacity of the strain was determined according to CLSI method. Intermediate products were identified using high-performance liquid chromatography, LC-MS/MS and (1) H NMR analysis. Intermediates were quantified by multiple reactions monitoring using LC-MS/MS. The strain was able to tolerate a high level of TA and utilized through enzymatic system. Growth of Azotobacter in TA-supplemented medium was characterized by an extended lag phase and decreased growth rate. Presence of TA catalytic enzymes as tannase, polyphenol oxidase (PPO) and phenol decarboxylase was confirmed in cell lysate using their specific substrates. PPO activity was more prominent in TA-supplemented mineral medium after 48 h of growth when gallic to ellagic acid (EA) reversible reaction was remarkable. Phase contrast and scanning electron microscopic analysis revealed elongated and irregular size of Azotobacter cells in response to TA. (1) H NMR analysis indicated that TA was transformed into gallic acid (GA), EA and pyrogallol. Biopolymer (EPS and PHB) production was decreased several folds in the presence of TA compared with cells grown in only glucose medium. CONCLUSIONS: This is the first evidence on the biotransformation of TA by Azotobacter and also elevated level of EA production from gallotannins. Azotobacter has developed the mechanism to utilize TA for their carbon and energy source. SIGNIFICANCE AND IMPACT OF THE STUDY: The widespread occurrence and exploitation of Azotobacter sp. strain SSB81 in agricultural and forest soil have an additional advantage to utilize the soil-accumulated TA and detoxifies the allelopathic effect of constant accumulated TA in soil.

Oral probiotics in coronavirus disease 2019: connecting the gut-lung axis to viral pathogenesis, inflammation, secondary infection and clinical trials.

Defined as helpful live bacteria that can provide medical advantages to the host when administered in tolerable amounts, oral probiotics might be worth considering as a possible preventive or therapeutic modality to mitigate coronavirus disease 2019 (COVID-19) symptom severity. This hypothesis stems from an emerging understanding of the gut-lung axis wherein probiotic microbial species in the digestive tract can influence systemic immunity, lung immunity, and possibly viral pathogenesis and secondary infection co-morbidities. We review the principles underlying the gut-lung axis, examples of probiotic-associated antiviral activities, and current clinical trials in COVID-19 based on oral probiotics.

Antimicrobial activity of leaf extract of Basilicum polystachyon (L) Moench.

Phenolic extract of leaves of Basilicum polystachyon (L) Moench was tested for in vitro antimicrobial activity against five bacteria (Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Bacillus subtilis, Micrococcus leuteus) and three fungi (Fusarium oxysporum, Aspergillus niger, Helminthosporium oryzae). Efficacy of organic solvents, methanol and ethanol, as agents for extraction was compared with acidic water (2M; HCl). High-pressure liquid chromatographic (HPLC) data showed that acidic extraction (2M; HCl) resulted in higher yield of caffeic acid (0.437 mg g(-1)) and rosmarinic acid (0.919 mg g(-1)). Acidic extract showed high activity against Gram (+) ve bacteria, but was less active against Gram (-) ve bacteria. Amongst the tested fungi, maximum activity was exhibited against Aspergillus niger. This is the first report on the phenolic constituents and bioactivity of B. polystachyon.

A rapid colony screening method for the detection of arsenate-reducing bacteria.

A rapid and simple method has been developed for the detection of arsenate reducing bacteria based on the presence of arsenite [As (III)], the end product of anaerobic arsenate [As (V)] respiration. Confirmation of As (III) product is made by the reduction of starch-iodine complex. The method can be used over a large pH range (5.5-9.0) and can easily be determined at arsenite concentration as low as 0.025 mM. Major advantages of this technique are that a large number of samples can be analyzed easily at a time.

YnfA , a SMR family efflux pump is abundant in Escherichia coli isolates from urinary infection.

A quantitative study was undertaken to determine the expression level of different efflux pumps in multi-drug-resistant (MDR) Escherichia coli isolates from urinary infection. We have determined the presence of different efflux pumps and measured the expression level of tolC, mdfA, norE and ynfA genes among 48 isolates by quantitative real-time PCR. The expression level of tolC and ynfA was constantly high and observed among 75-80% of isolates, whereas mdfA and norE were expressed occasionally. Our findings suggest that ynfA, a new SMR efflux pump gene family member increases the antibiotics' resistance in E. coli.

Pyrazine functionalized Ag(I) and Au(I)-NHC complexes are potential antibacterial agents.

Antimicrobial resistance is an ever-increasing problem throughout the world and has already reached severe proportions. Bacteria can develop ways to render traditional antibiotics ineffective, raising a crucial need to find new antimicrobials with novel mode of action. We demonstrate here a novel class of pyrazine functionalized Ag(I) and Au(I)-NHC complexes as antibacterial agents against human pathogens that are resistant to several antibiotics. Complete synthetic and structural studies of Au(I) and Ag(I) complexes of 2-(1-methylimidazolium) pyrimidinechloride (L-1), 2,6-bis(1-methylimidazol)pyrazinechloride (L-2) and 2,6-bis(1-methyl imidazol) pyrazinehexa-fluorophosphate (L-3) are reported herein. Chloro[2,6-bis(1-methyl imidazol)pyrazine]gold(I), 2b and chloro [2,6-bis(1-methyl imidazol)pyrazine]silver(I), 2a complexes are found to have more potent antimicrobial activity than other synthesized compounds and several conventionally used antibiotics. Complexes 2b and 2a also inhibit the biofilm formation by Gram-positive bacteria, Streptococcus mutans and Gram-negative bacteria, Escherichia coli, causing drastic damage to the bacterial cell wall and increasing membrane permeability. Complexes 2b and 2a strongly binds to both Lys and Dap-Type peptidoglycan layers, which may be the reason for damage to the bacterial cell wall. Theoretical studies of all the complexes reveal that 2b and 2a are more reactive than other complexes, and this may be the cause of differences in antibacterial activity. These findings will pave the way towards developing a new class of antibiotics against different groups of conventional antibiotic-resistant bacteria.