The influence of different concentrations of melatonin on the cell surface hydrophobic characteristics of Neisseria meningitidis

Bacteriostatic Potential of Melatonin: Therapeutic Standing and Mechanistic Insights

Diseases caused by pathogenic bacteria in animals (e.g., bacterial pneumonia, meningitis and sepsis) and plants (e.g., bacterial wilt, angular spot and canker) lead to high prevalence and mortality, and decomposition of plant leaves, respectively. Melatonin, an endogenous molecule, is highly pleiotropic, and accumulating evidence supports the notion that melatonin's actions in bacterial infection deserve particular attention. Here, we summarize the antibacterial effects of melatonin in vitro, in animals as well as plants, and discuss the potential mechanisms. Melatonin exerts antibacterial activities not only on classic gram-negative and -positive bacteria, but also on members of other bacterial groups, such as Mycobacterium tuberculosis. Protective actions against bacterial infections can occur at different levels. Direct actions of melatonin may occur only at very high concentrations, which is at the borderline of practical applicability. However, various indirect functions comprise activation of hosts' defense mechanisms or, in sepsis, attenuation of bacterially induced inflammation. In plants, its antibacterial functions involve the mitogen-activated protein kinase (MAPK) pathway; in animals, protection by melatonin against bacterially induced damage is associated with inhibition or activation of various signaling pathways, including key regulators such as NF-κB, STAT-1, Nrf2, NLRP3 inflammasome, MAPK and TLR-2/4. Moreover, melatonin can reduce formation of reactive oxygen and nitrogen species (ROS, RNS), promote detoxification and protect mitochondrial damage. Altogether, we propose that melatonin could be an effective approach against various pathogenic bacterial infections.

Utilizing melatonin to combat bacterial infections and septic injury

Melatonin, also known as N-acetyl-5-methoxytryptamine, is a ubiquitously acting molecule that is produced by the pineal gland and other organs of animals, including humans. As melatonin and its metabolites are potent antioxidants and free radical scavengers, they are protective against a variety of disorders. Moreover, multiple molecular targets of melatonin have been identified, and its actions are both receptor-mediated and receptor-independent. Recent studies have shown that melatonin may be useful in fighting against sepsis and septic injury due to its antioxidative and anti-inflammatory actions; the results generally indicate a promising therapeutic application for melatonin in the treatment of sepsis. To provide a comprehensive understanding regarding the protective effects of melatonin against septic injury, in the present review we have evaluated the published literature in which melatonin has been used to treat experimental and clinical sepsis. Firstly, we present the evidence from studies that have used melatonin to resist bacterial pathogens. Secondly, we illustrate the protective effect of melatonin against septic injury and discuss the possible mechanisms. Finally, the potential directions for future melatonin research against sepsis are summarized.

Surface adhesion and host response as pathogenicity factors of Neisseria meningitidis

Neisseria meningitidis (N. meningitidis) is an exclusively human pathogen that has been identified in 10%-35% of the adult population and in 5.9% of the child population. Despite the high prevalence of carriers of N. meningitidis, it only occasionally causes meningococcal disease in the context of endemic disease, in certain geographic areas or in isolated epidemic outbreaks. After the N. meningitidis genome is described, progress has been made toward understanding the pathogenic mechanisms of the bacteria, although some aspects concerning its interaction with the environment and the host remain unclear. Some studies have reported that oxidative stress in the environment can modify the surface characteristics of N. meningitidis, increasing its adhesive properties and favouring an asymptomatic carrier state. The antigenic structure of N. meningitidis can be modified by its importing genetic material from other bacteria in its ecological niche. Some structures of lipopolysaccharides help it to evade the immune response, and these are observed more frequently in N. meningitidis isolated from blood than in healthy nasopharyngeal carriers. There is evidence that pili and capsule are downregulated upon contact with target cells. This paper reviews current knowledge on host-environment-bacteria mechanisms and interactions, with the aim of contributing to our understanding of the pathogenic mechanisms of N. meningitidis.

Comparative study of the influence of melatonin and vitamin E on the surface characteristics of Escherichia coli

AIMS

Melatonin is a hormone produced by the pineal gland and that affects the response of various cell membranes to an oxidative stimulus.

METHODS AND RESULTS

The present study evaluates the hydrophobic characteristics of Escherichia coli in response to melatonin (100 nmol l(-1), 200 micromol l(-1)) and to vitamin E (5 mg dl(-1)). A reduction was found in the surface hydrophobicity of E. coli at concentrations of 200 micromol l(-1) melatonin in a Müeller-Hinton (MH) broth. These effects were modified when a protein synthesis inhibitor (chloramphenicol) was added at sub-lethal concentrations to the broth. Vitamin E produced a greater diminution in surface hydrophobicity than melatonin. The adherence of E. coli to nitrocellulose filters increased in the presence of melatonin + chloramphenicol, and vitamin E. The effects observed were independent of the concentration of iron in the broth.

CONCLUSION

Oxidative stress plays an important role in modifying the surface characteristics of E. coli, which could affect the micro-organism's capacity to adhere to epithelia.

SIGNIFICANCE AND IMPACT OF THE STUDY

We think that the oxide reduction potential of the host may be a determinant factor in the bacterial colonization of animal tissue.