Environmental hazard of polypropylene microplastics from disposable medical masks: acute toxicity towards Daphnia magna and current knowledge on other polypropylene microplastics

The COVID-19 pandemic has increased the use of disposable plastics, including medical masks, which have become a necessity in our daily lives. As these are often improperly disposed of, they represent an important potential source of microplastics in the environment. We prepared microplastics from polypropylene medical masks and characterised their size, shape, organic chemical leaching, and acute toxicity to the planktonic crustacean Daphnia magna. The three layers of the masks were separately milled and characterised. Each of the inner frontal, middle filtering, and outer layers yielded different types of microplastics: fibres were obtained from the inner and outer layer, but irregular fragments from the middle layer. The shape of the obtained microplastics differed from the initial fibrous structure of the intact medical mask layers, which indicates that the material is deformed during cryo-milling. The chemical compositions of plastics-associated chemicals also varied between the different layers. Typically, the inner layer contained more chemicals related to antimicrobial function and flavouring. The other two layers also contained antioxidants and their degradation products, plasticisers, cross-linking agents, antistatic agents, lubricants, and non-ionic surfactants. An acute study with D. magna showed that these microplastics do not cause immobility but do physically interact with the daphnids. Further long-term studies with these microplastics are needed using a suite of test organisms. Indeed, studies with other polypropylene microplastics have shown numerous adverse effects on other organisms at concentrations that have already been reported in the environment. Further efforts should be made to investigate the environmental hazards of polypropylene microplastics from medical masks and how to handle this new source of environmental burden.

Phytochemistry and In vitro Antimicrobial Activity of Five Plant Species against Nine Common Human Pathogens

Momordica charantia, Senna podocarpa, Senna alata, Ocimum gratissimum, and Sida acuta which have reportedly been used in folklore for the treatment of various diseases were studied for their antimicrobial activity. Crude methanolic extracts of the leaves were screened for phytochemicals after which they were tested in vitro for activity against clinical isolates of Staphylococcus aureus, Klebsiella oxytoca, Pseudomonas aeruginosa, Proteus vulgaris, Bacillus subtilis, Enterobacter aerogenes, Aspergillus niger, A, flavus and Candida albicans. Phytochemicals present in the extracts included saponins, alkaloids, anthraquinones, tannins, flavonoids and cardiac glycosides. These extracts also showed varying degrees of activity against tested organisms at a concentration range of 15.6 to 500 mg/ml. However, S. acuta showed activity against P. vulgaris, E. aerogenes and As. flavus only. The MIC of the extracts against test organisms ranged from 31.25 to 250 mg/ml. The significant antimicrobial susceptibility of the plant extracts against gram positive bacterial pathogens and some pathogenic yeasts, may not be due to the presence and synergistic interactions of secondary metabolites found in these plant extracts. This would have implications in health, particularly in developing countries where a singnificant percentage of the population are still using traditional plant extracts for health care. Dhaka Univ. J. Pharm. Sci. 20(2): 139-148, 2021 (December)

Estimation of the biosorption potential of certain representatives of the genus Bacillus in interaction with lead cation in vitro

The article presents data on the physicochemical and metabolically dependent mechanisms of detoxification by microorganisms of heavy metals that enter the environment during anthropogenic pollution. The taxonomic and physiological-biochemical diversity of microorganisms capable of neutralizing toxicants has been demonstrated. In the experimental part of the study, the combination of the methods used made it possible to fully assess the degree of toxicity and the effect of lead cations on the growth of bacteria of the genus Bacillus in a model experiment. Thus, the use of atomic absorption spectrophotometry and atomic force microscopy gave an idea of the level of biosorption of a given xenobiotic element from a substrate with localization of inactive forms of lead. The data obtained indicate the presence of an inhibitory effect of Pb (NO3) 2 and Pb (CH3COO) 2 in concentrations from 1 mM to 0.063 mM about the test organisms under study. The presence of cations with a nutrient substrate gives a false-positive idea of the degree of influence of lead on the growth of the studied microorganisms, since an increase in optical density in test samples is due to high sorption characteristics and, as a consequence, is characterized by an increase in relative optical density. An assessment of the detoxification mechanisms, which is expressed by active bioaccumulation of lead on the surface elements of the microbial cell up to 65% at the point of entering the stationary growth phase, indicates the promising use of representatives of this group of microorganisms as microbial bioremediation and correctors of excess content of this element in the body or ecosystem as a whole.

A Review of Microplastics Risk Assessment in the Coastal Environment

Pollution from microplastics has recently become a prevalent threat to the ecosystem. Microplastics with a dimension less than or equal to 5 mm are smaller. There are many ways that microplastics can reach the atmosphere. By various mechanisms, the breakdown of macro plastics will happen. Chemical degradation, tire abrasion, is the most common forms of degradation. Microplastics (MPs) pollution in the coastal and marine ecosystem is currently a global problem. Transferring MPs from land to sea and allowing them to enter the food chain has a direct negative impact on marine life and human health. The combined toxicity effects of MicroPlastics (MPs) and other contaminants in marine environments, as well as their toxicity effects and mechanisms based on a variety of environmentally important test organisms, were also covered in this study.

Syntheses, Characterization, and Antibacterial Evaluation of P. grandiflora Extracts Conjugated with Gold Nanoparticles

Background. With the recent increase in antibiotic resistance to conventional antibiotics, gold nanoparticles, and medicinal plants, extracts present an interesting alternative. Objectives. This study aimed to synthesize, characterize, and evaluate Pyrenacantha grandiflora Baill extracts and gold nanoparticle conjugates against pathogenic bacteria. Methods. We synthesized gold nanoparticles by chemical and biological methods. The nanoparticles were characterized by the use of UV-visible spectrophotometry, followed by transmission electron microscopy (TEM) and energy-dispersive X-ray analysis (EDX). Gold nanoparticles were conjugated to plant extracts and analyzed with a Fourier-transform infrared spectroscope (FTIR). We determined the antimicrobial activity of the conjugates using well diffusion and the microdilution assays. Results. The UV–visible spectra of gold nanoparticles showed a synthesis peak at 530 nm. FTIR analysis indicated functional biomolecules that were associated with plant extract conjugated gold nanoparticles; the formation of C–H group and carbonyl (C=O) groups, –OH carbonyl, and C≡C groups were also observed. Biologically synthesized nanoparticles were star-shaped when observed by TEM with an average size of 11 nm. Gold nanoparticles synthesized with P. grandiflora water extracts showed the largest zone of inhibition (22 mm). When the gold nanoparticles synthesized by the biological method were conjugated with acetone extracts of P. grandiflora, MIC as low as 0.0063 mg/mL was observed against beta-lactamase producing K. pneumonia. The activity of acetone extracts was improved with chemically synthesized gold nanoparticles particularly when beta-lactamase producing E. coli and MRSA were used as test organisms. A synergistic effect was observed against all tested bacteria, except for MRSA when gold nanoparticles were conjugated with acetone extract. Conclusion. Overall, P. grandiflora tuber extracts conjugated with gold nanoparticles showed a very good antibacterial activity that improved both plant extract and gold nanoparticle’s individual activity.

A Comparison of Antibacterial Potential of Different Soil Actinomycetes from Pokhara

Actinomycetes are widely distributed in the environment and used for the production of several important secondary metabolites like antibiotics, immunosuppressive agents, enzymes and antitumor agents. Therefore, the main objective of this study is to isolate and assess antibacterial potential of different actinomycetes obtained from different soil samples. This study was conducted in the microbiology laboratories of Prithvi Narayan Campus and Lambda Food Lab Pvt Ltd, Pokhara. A total of nine soil samples were collected from different places of Pokhara (forest land, agriculture land and lake bank) and processed. Isolated actinomycetes were screened by primary and secondary screening for antibiotic producers against test organisms like Staphylococcus aureus (ATCC 25923), Pseudomonas aeruginosa (ATCC 27853) and Bacillus spp, E coli (ATCC 25922). This study isolated 27 actinomycetes in total, using the soil samples through spread plating on Starch Casein Agar (SCA) and by serial dilution. After incubation, actinomycetes colonies (rough, chalky) were selected for gram staining to observe thin thread-like mycelial and hyphal structures. The highest number of actinomycetes isolates were obtained from agricultural land’s soil samples (14 out of 27 isolates i.e. 51.85%) whereas only 3 isolates were obtained from the lake soil. Primary screening was performed on Nutrient agar where test bacteria were streaked perpendicular to the isolated actinomycetes to observe antagonism. This showed 12 actinomycetes as active isolates inhibiting at least one test bacteria. The antibacterial compounds were extracted by ethyl acetate method and used in secondary screening. Secondary screening in Mueller Hinton agar (MHA) further revealed five isolates showed promising inhibitory capacity. In both screening methods higher sensitivity was observed towards Gram-positive bacteria especially S aureus (ATCC 25923), and the least sensitivity towards Gram-negative bacteria especially Pseudomonas aeruginosa (ATCC 27853). Agricultural land was shown to harbor more actinomycetes than forest land and lake bank soil. Though variations were observed in primary and secondary screening, actinomycetes obtained from agricultural land demonstrated an inhibitory action against the Gram-positive and Gram-negative test organisms. As compared to Gram-negative bacteria, the Gram-positive had higher effects. These findings showed that soil of different locations of Pokhara valley found many actinomycetes strains, preventing the growth of pathogenic bacteria of certain kinds. The study suggested that further investigations need to be done that helped obtain new antimicrobial agents from actinomycetes, using various other sources.

Phytochemical, Heavy Metals and Antimicrobial Study of the Leaves of Calopogonium Mucunoides

Background: In this study, the phytochemical, heavy metals, and antimicrobial characteristics of the leaves of Calopogonium mucunoides were investigated in other to determine its therapeutic potentials. The phytochemicals present in the leaves were extracted with n-hexane, methanol and ethyl acetate, and the extracts were used to investigate for the phytochemical constituents and antimicrobial activity. The methanol extract was used to test for the concentration of five heavy metals.Results: The result of the phytochemical screening confirmed the presence of alkaloids, anthocyanins, flavonoids, glycosides, phenols, reducing sugars, saponins, steroids, tannins, and terpenoids in various quantities. The heavy metals analysis result revealed the presence of lead (0.08 mg/kg) and iron (0.08 mg/kg) well below the acceptable limits set by the World Health Organization for heavy metals in plants, while cadmium, nickel and zinc were found to be below detectable limits. The extracts were tested against thirteen human pathogens (ten bacteria and three fungi) using the disk diffusion method. The extracts possessed a broad range of microbial activities, with the methanolic extract reportedly showing the highest zone of inhibition (31 mm) against Bacillus sp. while the n-hexane extract did not show any antimicrobial activity in the whole test organisms.Conclusion: The results obtained revealed that the leaves of C. mucunoides has some therapeutic values and could be exploited in the preparation of herbal drugs for the treatment of various ailments.

Astaxanthin-Mediated Bacterial Lethality: Evidence from Oxidative Stress Contribution and Molecular Dynamics Simulation

The involvement of cellular oxidative stress in antibacterial therapy has remained a topical issue over the years. In this study, the contribution of oxidative stress to astaxanthin-mediated bacterial lethality was evaluated in silico and in vitro. For the in vitro analysis, the minimum inhibitory concentration (MIC) of astaxanthin was lower than that of novobiocin against Staphylococcus aureus but generally higher than those of the reference antibiotics against other test organisms. The level of superoxide anion of the tested organisms increased significantly following treatment with astaxanthin when compared with DMSO-treated cells. This increase compared favorably with those observed with the reference antibiotics and was consistent with a decrease in the concentration of glutathione (GSH) and corresponding significant increase in ADP/ATP ratio. These observations are suggestive of probable involvement of oxidative stress in antibacterial capability of astaxanthin and in agreement with the results of the in silico evaluations, where the free energy scores of astaxanthins’ complexes with topoisomerase IV ParC and ParE were higher than those of the reference antibiotics. These observations were consistent with the structural stability and compactness of the complexes as astaxanthin was observed to be more stable against topoisomerase IV ParC and ParE than DNA Gyrase A and B. Put together, findings from this study underscored the nature and mechanism of antibacterial action of astaxanthin that could suggest practical approaches in enhancing our current knowledge of antibacterial arsenal and aid in the novel development of alternative natural topo2A inhibitor.