Functions and emerging applications of bacteriocins.

Introduction: The recent dramatic increase in the incidence of antimicrobial resistance has been recognized by organizations such as the United Nations and World Health Organization as well as the ...

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An overview of antimicrobial peptides and the latest advances in their development

Bacteriocins: Classification, synthesis, mechanism of action and resistance development in food spoilage causing bacteria.

Antibiotic resistance, prompted by the overuse of antimicrobial agents, may arise from a variety of mechanisms, particularly horizontal gene transfer of virulence and antibiotic resistance genes, which is often facilitated by biofilm formation. The importance of phenotypic changes seen in a biofilm, which lead to genotypic alterations, cannot be overstated. Irrespective of if the biofilm is single microbe or polymicrobial, bacteria, protected within a biofilm from the external environment, communicate through signal transduction pathways (e.g., quorum sensing or two-component systems), leading to global changes in gene expression, enhancing virulence, and expediting the acquisition of antibiotic resistance. Thus, one must examine a genetic change in virulence and resistance not only in the context of the biofilm but also as inextricably linked pathologies. Observationally, it is clear that increased virulence and the advent of antibiotic resistance often arise almost simultaneously; however, their genetic connection has been relatively ignored. Although the complexities of genetic regulation in a multispecies community may obscure a causative relationship, uncovering key genetic interactions between virulence and resistance in biofilm bacteria is essential to identifying new druggable targets, ultimately providing a drug discovery and development pathway to improve treatment options for chronic and recurring infection.

The Complex Relationship between Virulence and Antibiotic Resistance.

Curcuma longa is an important medicinal plant and a spice in Asia. Curcumin (diferuloylmethane) is a hydrophobic bioactive ingredient found in a rhizome of the C. longa. It has drawn immense attention in recent years for its variety of biological and pharmacological action. However, its low water solubility, poor bioavailability, and rapid metabolism represent major drawbacks for its successful therapeutic applications. Hence, researchers have attempted to enhance the biological and pharmacological activity of curcumin and overcome its drawbacks by efficient delivery systems, particularly nanoencapsulation. Research efforts so far and data from the available literature have shown a satisfactory potential of nanorange formulations of curcumin (Nanocurcumin), it increases all the biological and pharmacological benefits of curcumin, which was not significantly possible earlier. For the synthesis of nanocurcumin, an array of techniques has been developed and each technique has its own advantages and individual characteristics. The two most popular and effective techniques are ionic gelation and antisolvent precipitation. So far, many curcumin nanoformulations have been developed to enhance curcumin delivery, thereby overcoming the low therapeutic eﬀects. However, most of the nanoformulation of curcumin remained at the concept level evidence, thus, several questions and challenges still exist to recommend the nanocurcumin as a promising candidate for therapeutic applications. In this review, we discuss the different curcumin nanoformulation and nanocurcumin implications for different therapeutic applications as well as the status of ongoing clinical trials and patents. We also discuss the research gap and future research directions needed to propose curcumin as a promising therapeutic candidate.

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Nanocurcumin: A Promising Candidate for Therapeutic Applications.

Biofilm-associated bacteria are less sensitive to antibiotics than free-living (planktonic) cells. Furthermore, with variations in the concentration of antibiotics throughout a biofilm, microbial cells are often exposed to levels below inhibitory concentrations and may develop resistance. This, as well as the irresponsible use of antibiotics, leads to the selection of pathogens that are difficult to eradicate. The Centers for Disease Control and Prevention use the terms "antibiotic" and "antimicrobial agent" interchangeably. However, a clear distinction between these two terms is required for the purpose of this assessment. Therefore, we define "antibiotics" as pharmaceutically formulated and medically administered substances and "antimicrobials" as a broad category of substances which are not regulated as drugs. This comprehensive minireview evaluates the effect of natural antimicrobials on pathogens in biofilms when used instead of, or in combination with, commonly prescribed antibiotics.

Control of Biofilm Formation: Antibiotics and Beyond

Curcumin, a hydrophobic phenolic compound isolated from tumeric (Curcuma longa), has gained a great attention due to its health benefits and antimicrobial effects. In this study, curcumin nanoparticles (CNPs) were formulated via acusto-plastic deformation technique, with three differently surface-charged surfactants-sodium dodecylsulfate, Tween 20 and cetrimonium bromide (CTAB). The fabricated CNPs were evaluated for their antimicrobial activity against Listeria monocytogenes, one of the most severe foodborne pathogens. Our results demonstrated that the CNPs formulated with positively charged surfactant (CTAB) exhibited the highest antimicrobial activity against L. monocytogenes, indicating that there is a strong relationship between surface charge and antimicrobial activity of curcumin. The enhanced antimicrobial action of CNPs-CTAB was concluded to be due to the increased cell-antimicrobial interaction, which resulted from the opposing electrical charges between CNPs-CTAB and L. monocytogenes cells, as well as increased antimicrobial penetration endowed by the small size.

Practical applications
In this study, we showed that surface charge as well as the small size of curcumin nanoparticles play a key role in enhancing cell-antimicrobial interaction and antimicrobial efficacy. The fabricated CNP-CTAB showed the best antimicrobial activity against Listeria monocytogenes. A size reduction to nano-scale is a recently developed strategy used to improve drug/food delivery and matching the public demand for effective and safe antimicrobial formulations for control of foodborne pathogens.

Antimicrobial efficacy of curcumin nanoparticles against Listeria monocytogenes is mediated by surface charge

Antibiotic resistance and recurrence of bacterial vaginosis (BV), a polymicrobial infection, justify the need for novel antimicrobials to counteract microbial resistance to conventional antibiotics. Previously, two series of cationic amphiphiles (CAms) which self-assemble into supramolecular nanostructures with membrane-lytic properties were designed with hydrophilic head groups and nonpolar domains. The combination of CAms and commonly prescribed antibiotics is suggested as a promising strategy for targeting microorganisms that are resistant to conventional antibiotics. Activities of the CAms against Gardnerella vaginalis ATCC 14018, a representative BV pathogen, ranged from 1.1 to 24.4 μM. Interestingly, the tested healthy Lactobacillus species, especially Lactobacillus plantarum ATCC 39268, were significantly more tolerant of CAms than the selected pathogens. In addition, CAms prevented biofilm formation at concentrations which did not influence the normal growth ability of G. vaginalis ATCC 14018. Furthermore, the biofilm minimum bactericidal concentration (MBC-Bs) of CAms against G. vaginalis ATCC 14018 ranged from 58.8 to 425.6 μM, while much higher concentrations (≥850 μM) were required to produce ≥3-log reductions in the number of biofilm-associated lactobacilli. The conventional antibiotic metronidazole synergized strongly with all tested CAms against planktonic cells and biofilms of G. vaginalis ATCC 14018. The synergism between CAms and the tested conventional antibiotic may be considered a new, effective, and beneficial method of controlling biofilm-associated bacterial vaginosis.

Gemini Cationic Amphiphiles Control Biofilm Formation by Bacterial Vaginosis Pathogens.

https://journals.asm.org/doi/pdf/10.1128/AEM.00165-17

Nicole Comito

Papers

Control of Biofilm Formation: Antibiotics and Beyond

Antimicrobial efficacy of curcumin nanoparticles against Listeria monocytogenes is mediated by surface charge

Gemini Cationic Amphiphiles Control Biofilm Formation by Bacterial Vaginosis Pathogens.

Erratum for Algburi et al., Control of Biofilm Formation: Antibiotics and Beyond.