Effect of a novel antimicrobial peptide chrysophsin-1 on oral pathogens and Streptococcus mutans biofilms

Chicken NK-lysin is an alpha-helical cationic peptide that exerts its antibacterial activity through damage of bacterial cell membranes

The antimicrobial peptides (AMP) are important elements of the first line of defense against pathogens in animals, and an important constituent of innate immunity. Antimicrobial peptides act on a broad spectrum of microbial organisms. NK-Lysin is a cationic antibacterial peptide that was originally isolated from porcine intestinal tissue based on its antibacterial activity. We synthesized peptides corresponding to each helical region of chicken NK-lysin and analyzed their secondary structures in addition to their antimicrobial activity. Circular dichroism spectroscopy of the synthetic chicken NK-lysin (cNK-78) and 4 small peptides in negatively charged liposomes demonstrated transition in the conformation of α-helical peptides relative to the charged environment. Chicken NK-lysin inhibits the growth of a representative gram-negative bacterium, Escherichia coli. The antimicrobial activity of 2 peptides designated H23 and H34 was similar to that of mature NK-lysin, cNK-78. Microscopic analyses revealed the death of bacterium with disrupted membranes after peptide treatment, suggesting that chicken NK-lysin, an alpha-helical cationic peptide, exerts its antimicrobial activity by damaging the bacterial cell membrane.

The virulence of Streptococcus mutans and the ability to form biofilms

In some diseases, a very important role is played by the ability of bacteria to form multi-dimensional complex structure known as biofilm. The most common disease of the oral cavity, known as dental caries, is a top leader. Streptococcus mutans, one of the many etiological factors of dental caries, is a microorganism which is able to acquire new properties allowing for the expression of pathogenicity determinants determining its virulence in specific environmental conditions. Through the mechanism of adhesion to a solid surface, S. mutans is capable of colonizing the oral cavity and also of forming bacterial biofilm. Additional properties enabling S. mutans to colonize the oral cavity include the ability to survive in an acidic environment and specific interaction with other microorganisms colonizing this ecosystem. This review is an attempt to establish which characteristics associated with biofilm formation--virulence determinants of S. mutans--are responsible for the development of dental caries. In order to extend the knowledge of the nature of Streptococcus infections, an attempt to face the following problems will be made: Biofilm formation as a complex process of protein-bacterium interaction. To what extent do microorganisms of the cariogenic flora exemplified by S. mutans differ in virulence determinants "expression" from microorganisms of physiological flora? How does the environment of the oral cavity and its microorganisms affect the biofilm formation of dominant species? How do selected inhibitors affect the biofilm formation of cariogenic microorganisms?

Antimicrobial peptides from fish

Antimicrobial peptides (AMPs) are found widely distributed through Nature, and participate in the innate host defense of each species. Fish are a great source of these peptides, as they express all of the major classes of AMPs, including defensins, cathelicidins, hepcidins, histone-derived peptides, and a fish-specific class of the cecropin family, called piscidins. As with other species, the fish peptides exhibit broad-spectrum antimicrobial activity, killing both fish and human pathogens. They are also immunomodulatory, and their genes are highly responsive to microbes and innate immuno-stimulatory molecules. Recent research has demonstrated that some of the unique properties of fish peptides, including their ability to act even in very high salt concentrations, make them good potential targets for development as therapeutic antimicrobials. Further, the stimulation of their gene expression by exogenous factors could be useful in preventing pathogenic microbes in aquaculture.

Antimicrobial and anti-biofilm effect of Bac8c on major bacteria associated with dental caries and Streptococcus mutans biofilms

Dental caries is a common oral bacterial infectious disease. Its prevention and treatment requires control of the causative pathogens within dental plaque, especially Streptococcus mutans (S. mutans). Antimicrobial peptides (AMPs), one of the promising substitutes for conventional antibiotics, have been widely tested and used for controlling bacterial infections. The present study focuses on evaluating the potential of the novel AMPs cyclic bactenecin and its derivatives against bacteria associated with dental caries. The results indicate that Bac8c displayed highest activity against the bacteria tested, whereas both cyclic and linear bactenecin had weak antimicrobial activity. The cytotoxicity assay showed that Bac8c did not cause detectable toxicity at concentrations of 32-128μg/ml for 5min or 32-64μg/ml for 60min. S. mutans and Lactobacillus fermenti treated with Bac8c showed variable effects on bacterial structure via scanning electron microscopy and transmission electron microscopy. There appeared to be a large amount of extracellular debris and obvious holes on the cell surface, as well as loss of cell wall and nucleoid condensation. The BioFlux system was employed to generate S. mutans biofilms under a controlled flow, which more closely resemble the formation process of natural biofilms. Bac8c remarkably reduced the viability of cells in biofilms formed in the BioFlux system. This phenomenon was further analyzed and verified by real-time PCR results of a significant suppression of the genes involved in S. mutans biofilm formation. Taken together, this study suggests that Bac8c has a potential clinical application in preventing and treating dental caries.

Field emission scanning electron microscopy of biofilm-growing bacteria involved in nosocomial infections

Scanning electron microscopy (SEM) provides useful information on the shape, size, and localization within the biofilm of single bacteria as well as on the steps of biofilm formation process, on bacterial interactions, and on production of extracellular polymeric substances.When biofilms are constituted by microbial species involved in health care-associated infections, information provided by SEM can be fruitfully used not only for basic researches but also for diagnostic purposes.The protocols currently used in our laboratory for biofilm investigation by SEM are reported here. Particularly, the procedures to fix, dehydrate, and metalize in vitro-developed biofilms or ex vivo clinical specimens colonized by biofilm-growing microorganisms are described as well as the advantages of the observation of these samples by field emission scanning electron microscopy.

In vitro pharmacokinetics of antimicrobial cationic peptides alone and in combination with antibiotics against methicillin resistant Staphylococcus aureus biofilms

Antibiotic therapy for methicillin-resistant Staphylococcus aureus (MRSA) infections is becoming more difficult in hospitals and communities because of strong biofilm-forming properties and multidrug resistance. Biofilm-associated MRSA is not affected by therapeutically achievable concentrations of antibiotics. Therefore, we investigated the in vitro pharmacokinetic activities of antimicrobial cationic peptides (AMPs; indolicidin, cecropin [1-7]-melittin A [2-9] amide [CAMA], and nisin), either alone or in combination with antibiotics (daptomycin, linezolid, teicoplanin, ciprofloxacin, and azithromycin), against standard and 2 clinically obtained MRSA biofilms. The minimum inhibitory concentrations (MIC) and minimum biofilm-eradication concentrations (MBEC) were determined by microbroth dilution technique. The time-kill curve (TKC) method was used to determine the bactericidal activities of the AMPs alone and in combination with the antibiotics against standard and clinically obtained MRSA biofilms. The MIC values of the AMPs and antibiotics ranged between 2 to 16 and 0.25 to 512 mg/L, and their MBEC values were 640 and 512 to 5120 mg/L, respectively. The TKC studies demonstrated that synergistic interactions occurred most frequently when using nisin+daptomycin/ciprofloxacin, indolicidin+teicoplanin, and CAMA+ciprofloxacin combinations. No antagonism was observed with any combination. AMPs appear to be good candidates for the treatment of MRSA biofilms, as they act as both enhancers of anti-biofilm activities and help to prevent or delay the emergence of resistance when used either alone or in combination with antibiotics.

Time-kill behaviour against eight bacterial species and cytotoxicity of antibacterial monomers

OBJECTIVES

The objectives of this study were to investigate: (1) the antibacterial activity of two antibacterial monomers, dimethylaminododecyl methacrylate (DMADDM) and dimethylammoniumethyl dimethacrylate (DMAEDM), against eight different species of oral pathogens for the first time; (2) the cytotoxicity of DMAEDM and DMADDM.

METHODS

DMAEDM and DMADDM were synthesized by reacting a tertiary amine group with an organo-halide. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) against eight species of bacteria were tested. Time-kill determinations were performed to examine the bactericidal kinetics. Cytotoxicity of monomers on human gingival fibroblasts (HGF) was assessed using a methyl thiazolyltetrazolium assay and live/dead viability assay.

RESULTS

DMADDM showed strong bactericidal activity against all bacteria, with MIC of 1.2-9.8μg/mL. DMAEDM had MIC of 20-80mg/mL. Time-kill determinations indicated that DMADDM and DMAEDM had rapid killing effects against eight species of bacteria, and eliminated all bacteria in 30min at the concentration of 4-fold MBC. Median lethal concentration for DMADDM and DMAEDM was between 20 and 40μg/mL, which was 20-fold higher than 1-2μg/mL for BisGMA control.

CONCLUSIONS

DMAEDM and DMADDM were tested in time-kill assay against eight species of oral bacteria for the first time. Both were effective in bacteria-inhibition, but DMADDM had a higher potency than DMAEDM. Different killing efficacy was found against different bacteria species. DMAEDM and DMADDM had much lower cytotoxicity than BisGMA. Therefore, DMADDM and DMAEDM are promising for use in bonding agents and other restorative/preventive materials to combat a variety of oral pathogens.

The pathogenicity of the Streptococcus genus

Streptococcus infections are still one of the important problems facing contemporary medicine. As the World Health Organization (WHO) warns, Streptococcus pneumoniae is responsible for the highest number of pneumonia cases all over the world. Despite an increasing number of pneumococcal vaccinations, incidences of disease connected to this pathogen's infection stay at the same level, which is related to a constantly increasing number of infections caused by nonvaccinal serotypes. Unfortunately, the pathogenicity of bacteria of the Streptococcus genus is also connected to species considered to be physiological flora in humans or animals and, additionally, new species exhibiting pathogenic potential have been discovered. This paper presents an opinion concerning the epidemiology of streptococci infections based on case studies and other publications devoted to this problem. It also sheds new light based on recent reports on the prevention of protective vaccinations application in the case of streptococci infections.

Tannins possessing bacteriostatic effect impair Pseudomonas aeruginosa adhesion and biofilm formation

Plants produce many compounds that are biologically active, either as part of their normal program of growth and development or in response to pathogen attack or stress. Traditionally, Anadenanthera colubrina, Commiphora leptophloeos and Myracrodruon urundeuva have been used by communities in the Brazilian Caatinga to treat several infectious diseases. The ability to impair bacterial adhesion represents an ideal strategy to combat bacterial pathogenesis, because of its importance in the early stages of the infectious process; thus, the search for anti-adherent compounds in plants is a very promising alternative. This study investigated the ability of stem-bark extracts from these three species to control the growth and prevent biofilm formation of Pseudomonas aeruginosa, an important opportunistic pathogen that adheres to surfaces and forms protective biofilms. A kinetic study (0–72 h) demonstrated that the growth of extract-treated bacteria was inhibited up to 9 h after incubation, suggesting a bacteriostatic activity. Transmission electron microscopy and fluorescence microscopy showed both viable and nonviable cells, indicating bacterial membrane damage; crystal violet assay and scanning electron microscopy demonstrated that treatment strongly inhibited biofilm formation during 6 and 24 h and that matrix production remained impaired even after growth was restored, at 24 and 48 h of incubation. Herein, we propose that the identified (condensed and hydrolyzable) tannins are able to inhibit biofilm formation via bacteriostatic properties, damaging the bacterial membrane and hindering matrix production. Our findings demonstrate the importance of this abundant class of Natural Products in higher plants against one of the most challenging issues in the hospital setting: biofilm resilience.

Antimicrobial activity of the synthetic peptide Lys-a1 against oral streptococci

The peptide LYS-[TRP(6)]-Hy-A1 (Lys-a1) is a synthetic derivative of the peptide Hy-A1, initially isolated from the frog species Hypsiboas albopunctatus. According to previous research, it is a molecule with broad antimicrobial activity. The objective of this study was to evaluate the antimicrobial activity of the synthetic peptide Lys-a1 (KIFGAIWPLALGALKNLIK-NH2) on the planktonic and biofilm growth of oral bacteria. The methods used to evaluate antimicrobial activity include the following: determination of the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) in microtiter plates for growth in suspension and quantification of biomass by crystal violet staining and counting of colony forming units for biofilm growth. The microorganisms Streptococcus oralis, Streptococcus sanguinis, Streptococcus parasanguinis, Streptococcus salivarius, Streptococcus mutans and Streptococcus sobrinus were grown in Brain Heart Infusion broth at 37°C under atmospheric pressure with 10% CO2. The peptide was solubilized in 0.1% acetic acid (v/v) at various concentrations (500-1.9 μg mL(-1)). Chlorhexidine gluconate 0.12% was used as the positive control, and BHI culture medium was used as the negative control. The tested peptide demonstrated a remarkable antimicrobial effect, inhibiting the planktonic and biofilm growth of all strains tested, even at low concentrations. Thus, the peptide Lys-a1 is an important source for potential antimicrobial agents, especially for the control and prevention of microbial biofilms, which is one of the most important factors in cariogenic processes.

Screening of aqueous extracts of medicinal herbs for antimicrobial activity against oral bacteria

Background

Dental caries is considered to be a preventable disease, and various antimicrobial agents have been developed for the prevention of dental diseases; however, many bacteria show resistance to existing agents. In this study, 14 medicinal herbs were evaluated for antimicrobial activity against five common oral bacteria as a screen for potential candidates for the development of natural antibiotics.

Methods

Aqueous extracts of medicinal herbs were tested for activity against Enterococcus faecalis, Actinomyces viscosus, Streptococcus salivarius, Streptococcus mutans, and Streptococcus sanguis grown in brain heart infusion (BHI) broth. A broth microdilution assay was used to determine the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). A disk diffusion assay was performed by inoculating bacterial cultures on BHI agar plates with paper disks soaked in each of the medicinal herb extracts. Inhibition of the synthesis of water-insoluble glucans by S. mutans was also investigated.

Results

The aqueous extracts of many of the 14 medicinal herbs demonstrated antimicrobial activity against the five types of pathogenic oral bacteria. The extracts of Sappan Lignum, Coptidis Rhizoma, and Psoraleae Semen effectively inhibited the growth of oral bacteria and showed distinct bactericidal activity. The extracts of Notoginseng Radix, Perillae Herba, and Psoraleae Semen decreased the synthesis of water-insoluble glucans by the S. mutans enzyme glucosyltransferase (GTase). The present study is the first to confirm the antimicrobial activity of the extract of Sappan Lignum against all five species of oral bacteria strains.

Conclusion

These results suggest that certain herbal medicines with proven antimicrobial effects, such as Sappan Lignum and Psoraleae Semen, may be useful for the treatment of dental diseases.

New trends in peptide-based anti-biofilm strategies: a review of recent achievements and bioinformatic approaches

Antimicrobial peptides (AMPs) have a broad spectrum of activity and unspecific mechanisms of action. Therefore, they are seen as valid alternatives to overcome clinically relevant biofilms and reduce the chance of acquired resistance. This paper reviews AMPs and anti-biofilm AMP-based strategies and discusses ongoing and future work. Recent studies report successful AMP-based prophylactic and therapeutic strategies, several databases catalogue AMP information and analysis tools, and novel bioinformatics tools are supporting AMP discovery and design. However, most AMP studies are performed with planktonic cultures, and most studies on sessile cells test AMPs on growing rather than mature biofilms. Promising preliminary synergistic studies have to be consubstantiated and the study of functionalized coatings with AMPs must be further explored. Standardized operating protocols, to enforce the repeatability and reproducibility of AMP anti-biofilm tests, and automated means of screening and processing the ever-expanding literature are still missing.