The ability of probiotic bacteria to adhere to the intestinal epithelium play an important role in colonization of the gastrointestinal tract, preventing their elimination by peristalsis and providing a competitive advantage in this ecosystem. To identify bacterial traits related to adhesion the probiotic strain L. acidophilus M92 was examined for autoaggregation ability and cell surface hydrophobicity L. acidophilus M92 exhibits a strong autoaggregation phenotype and also coaggregation with some pathogen microorganisms that may form a barrier that prevents their colonization. The examined probiotic strain manifests a good degree of hydrophobicity determined by microbial adhesion to hydrocarbons. Aggregation and hydrophobicity were abolished upon exposure of the cells to pronase, which suggests the possible role of cell surface layer (S-layer) proteins, approximated at 45 kDa, in a L. acidophilus M92. The relationship between autoaggregation and adhesion ability to intestinal tissue was investigated by observing the adhesivity of L. acidophilus M92 to porcine ileal epithelial cells. Removal of the S-layer proteins by extraction with 5 M LiCl reduced autaggregation and in vitro adhesion of this strain.

Adhesion and aggregation ability of probiotic strain Lactobacillus acidophilus M92

Since discovery of the first antibiotic drug, penicillin, in 1928, a variety of antibiotic and antimicrobial agents have been developed and used for both human therapy and industrial applications. However, excess and uncontrolled use of antibiotic agents has caused a significant growth in the number of drug resistant pathogens. Novel therapeutic approaches replacing the inefficient antibiotics are in high demand to overcome increasing microbial multidrug resistance. In the recent years, ongoing research has focused on development of nano-scale objects as efficient antimicrobial therapies. Among the various nanoparticles, silver nanoparticles have gained much attention due to their unique antimicrobial properties. However, concerns about the synthesis of these materials such as use of precursor chemicals and toxic solvents, and generation of toxic byproducts have led to a new alternative approach, green synthesis. This eco-friendly technique incorporates use of biological agents, plants or microbial agents as reducing and capping agents. Silver nanoparticles synthesized by green chemistry offer a novel and potential alternative to chemically synthesized nanoparticles. In this review, we discuss the recent advances in green synthesis of silver nanoparticles, their application as antimicrobial agents and mechanism of antimicrobial mode of action.

https://pubs.rsc.org/en/content/articlepdf/2019/ra/c8ra08982e

Green synthesis of silver nanoparticles: biomolecule-nanoparticle organizations targeting antimicrobial activity

Infection, as a common postoperative complication of orthopedic surgery, is the main reason leading to implant failure. Silver nanoparticles (AgNPs) are considered as a promising antibacterial agent and always used to modify orthopedic implants to prevent infection. To optimize the implants in a reasonable manner, it is critical for us to know the specific antibacterial mechanism, which is still unclear. In this review, we analyzed the potential antibacterial mechanisms of AgNPs, and the influences of AgNPs on osteogenic-related cells, including cellular adhesion, proliferation, and differentiation, were also discussed. In addition, methods to enhance biocompatibility of AgNPs as well as advanced implants modifications technologies were also summarized.

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Potential antibacterial mechanism of silver nanoparticles and the optimization of orthopedic implants by advanced modification technologies.

Metal nanoparticles have received great attention from researchers across the world because of a plethora of applications in agriculture and the biomedical field as antioxidants and antimicrobial compounds. Over the past few years, green nanotechnology has emerged as a significant approach for the synthesis and fabrication of metal nanoparticles. This green route employs various reducing and stabilizing agents from biological resources for the synthesis of nanoparticles. The present article aims to review the progress made in recent years on nanoparticle biosynthesis by microbes. These microbial resources include bacteria, fungi, yeast, algae and viruses. This review mainly focuses on the biosynthesis of the most commonly studied metal and metal salt nanoparticles such as silver, gold, platinum, palladium, copper, cadmium, titanium oxide, zinc oxide and cadmium sulphide. These nanoparticles can be used in pharmaceutical products as antimicrobial and anti-biofilm agents, targeted delivery of anticancer drugs, water electrolysis, waste water treatment, biosensors, biocatalysis, crop protection against pathogens, degradation of dyes etc. This review will discuss in detail various microbial modes of nanoparticles synthesis and the mechanism of their synthesis by various bioreducing agents such as enzymes, peptides, proteins, electron shuttle quinones and exopolysaccharides. A thorough understanding of the molecular mechanism of biosynthesis is the need of the hour to develop a technology for large scale production of bio-mediated nanoparticles. The present review also discusses the advantages of various microbial approaches in nanoparticles synthesis and lacuna involved in such processes. This review also highlights the recent milestones achieved on large scale production and future perspectives of nanoparticles.

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A review on the biosynthesis of metal and metal salt nanoparticles by microbes

Over the last seven decades, applications using members of the Bacillus subtilis group have emerged in both food processes and crop protection industries. Their ability to form survival endospores and the plethora of antimicrobial compounds they produce has generated an increased industrial interest as food preservatives, therapeutic agents and biopesticides. In the growing context of food biopreservation and biological crop protection, this review suggests a comprehensive way to visualize the antimicrobial spectrum described within the B. subtilis group, including volatile compounds. This classification distinguishes the bioactive metabolites based on their biosynthetic pathways and chemical nature: i.e., ribosomal peptides (RPs), volatile compounds, polyketides (PKs), non-ribosomal peptides (NRPs), and hybrids between PKs and NRPs. For each clade, the chemical structure, biosynthesis and antimicrobial activity are described and exemplified. This review aims at constituting a convenient and updated classification of antimicrobial metabolites from the B. subtilis group, whose complex phylogeny is prone to further development.

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Overview of the Antimicrobial Compounds Produced by Members of the Bacillus subtilis Group.

The human gut microbiota has received considerable interest in the recent years and our knowledge of the inhabitant species and their potential applications is increased particularly after the development of metagenomic studies. Gut microbiota is highly diverse and harboring trillions of microorganisms in human digestive system. The shaping and multiplication of gut microbiome starts at birth, while the modification of their composition depends mainly on various genetic, nutritional and environmental factors. The modification in the composition and function of the gut microbiota can change intestinal permeability, digestion and metabolism as well as immune responses. The pro inflammatory state caused by alternation of gut microbiota balance lead to the onset of many diseases ranging from gastrointestinal and metabolic conditions to immunological and neuropsychiatric diseases. In this context, the present review clarifies the role of gut microbiota in maintaining host health and investigates how nutritional and environmental factors affect the gut microbial structure and function. In addition, many therapeutic strategies of gut microbiota aimed at modulating and restoring of the intestinal ecosystem balance have been surveyed.

Human gut microbiota/microbiome in health and diseases: a review

Thirty bacterial strains were isolated from the rhizosphere of plants collected from Egypt and screened for production of chitinase enzymes. Bacillus thuringiensis NM101-19 and Bacillus licheniformis NM120-17 had the highest chitinolytic activities amongst those investigated. The production of chitinase by B. thuringiensis and B. licheniformis was optimized using colloidal chitin medium amended with 1.5% colloidal chitin, with casein as a nitrogen source, at 30°C after five days of incubation. An enhancement of chitinase production by the two species was observed by addition of sugar substances and dried fungal mats to the colloidal chitin media. The optimal conditions for chitinase activity by B. thuringiensis and B. licheniformis were at 40°C, pH 7.0 and pH 8.0, respectively. Na+, Mg2+, Cu2+, and Ca2+ caused enhancement of enzyme activities whereas they were markedly inhibited by Zn2+, Hg2+, and Ag+. In vitro, B. thuringiensis and B. licheniformis chitinases had potential for cell wall lysis of many phytopathogenic fungi tested. The addition of B. thuringiensis chitinase was more effective than that of B. licheniformis in increasing the germination of soybean seeds infected with various phytopathogenic fungi.

Chitinase production by Bacillus thuringiensis and Bacillus licheniformis: their potential in antifungal biocontrol.

Antimicrobial, antioxidant and antitumor activities of silver nanoparticles synthesized by Allium cepa extract: A green approach

The current research was focused on the characterization and antimicrobial activity of silver nanoparticles (AgNPs) produced by Bacillus licheniformis NM120-17. The synthesis was initially observed by a colour change from pale yellow to brown which was further confirmed by UV-Vis spectroscopy. The AgNPs were characterized using TEM, EDAX and FTIR. The synthesized nanoparticles were found to be spherical and uniformly distributed with a size in the range of 9-27.5 nm. The antibacterial activities and acting mechanism of AgNPs were studied with respect to Staphylococcus aureus and Escherichia coli by measuring the growth curves, protein and reducing sugar leakage, respiratory chain dehydrogenase activity, as well as the formation of bactericidal reactive oxygen species (ROS). The experimental results indicated that 50 mg/ml AgNPs could completely inhibit the growth of bacterial cells and destroy the permeability of bacterial membranes and depress the activity of some membranous enzymes, which cause bacteria to die eventually. These nontoxic nanomaterials, which can be prepared in a simple and cost-effective manner, may be suitable for the formulation of new types of bactericidal materials.

Silver nanoparticles as an antimicrobial agent: A case study on Staphylococcus aureus and Escherichia coli as models for Gram-positive and Gram-negative bacteria.

This study aimed to investigate the antimicrobial and anti-adhesive properties of biosurfactant extracted from ten lactobacilli species isolated from Egyptian dairy products. The produced biosurfactants showed distinct antimicrobial and anti-adhesive activities against several pathogenic microorganisms. Furthermore, lactobacilli isolates were studied for biofilm formation and lactic acid production in different growth media. All lactobacilli isolates produced biofilm on polystyrene surface in all media tested to different degrees. L. acidophilus showed the highest biofilm formation in Rogosa medium. However, the highest lactic acid production was recorded by L. brevis (39.63 g/L), followed by L. reuteri (33.32 g/L) in MRS medium. Evaluation based on in vitro studies including auto-aggregation and co-aggregation with three pathogenic bacterial strains was further analyzed. All lactobacilli isolates tested were able to auto-aggregate (ranging from 51.12% to 78.17% assessed at 5 h of incubation). The lactobacilli isolates co-aggregate with the tested bacterial strains to different degrees; among them L. delbrueckii showed the highest scores of co-aggregation with Candida albicans ATC70014, reaching 59.37%. The aggregation ability exhibited by the isolated lactobacilli, together with the antimicrobial and anti-adhesive properties observed for their biosurfactants, opens future prospects for their use against microorganisms responsible for diseases and infections and as effective probiotic strains.

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Eman Zakaria Gomaa

Papers

Human gut microbiota/microbiome in health and diseases: a review

Chitinase production by Bacillus thuringiensis and Bacillus licheniformis: their potential in antifungal biocontrol.

Antimicrobial, antioxidant and antitumor activities of silver nanoparticles synthesized by Allium cepa extract: A green approach

Silver nanoparticles as an antimicrobial agent: A case study on Staphylococcus aureus and Escherichia coli as models for Gram-positive and Gram-negative bacteria.

Antimicrobial and anti-adhesive properties of biosurfactant produced by lactobacilli isolates, biofilm formation and aggregation ability.