Production of antagonistic substance by Eikenella corrodens isolated from the oral cavity of human beings with and without periodontal disease

Porphyromonas gingivalis: where do we stand in our battle against this oral pathogen?

Periodontal diseases, such as gingivitis and periodontitis, are inflammatory diseases triggered by pathogenic bacteria that lead to damage of the soft tissue and bone supporting the teeth. Amongst the identified oral periodontopathogenic bacteria, Porphyromonas gingivalis is able to enhance oral dysbiosis, which is an imbalance in the beneficial commensal and periodontal pathogenic bacteria that induces chronic inflammation. Given the critical role of oral pathogenic bacteria like P. gingivalis in the pathogenesis of periodontitis, local and/or systemic antibacterial therapy has been suggested to treat this disease, especially in its severe or refractory forms. Nevertheless, the majority of the antibacterial agents currently used for the treatment of periodontal diseases are broad-spectrum, which harms beneficial bacterial species that are critical in health, inhibit the growth of pathogenic bacteria, contribute in protecting the periodontal tissues to damage and aid in its healing. Thus, the development of more effective and specific antibacterial agents is needed to control oral pathogens in a polymicrobial environment. The strategies for the development of novel antibacterial agents include natural product isolation as well as synthetic and semi-synthetic methodologies. This review presents an overview of the periodontal diseases gingivitis and periodontitis along with current antibacterial treatment options (i.e., classes of antibacterial agents and the mechanism(s) of resistance that hinder their usage) used in periodontal diseases that specifically target oral pathogens such as P. gingivalis. In addition, to help medicinal chemists gain a better understanding of potentially promising scaffolds, this review provides an in-depth coverage of the various families of small molecules that have been investigated as potential anti-P. gingivalis agents, including novel families of compounds, repositioned drugs, as well as natural products.

Inter-bacterial correlations in subgingival biofilms: a large-scale survey

AIM

Although the complexity of the oral ecology and the ecological differences between health and disease are well accepted, a clear view on the dynamics in relation to disease is lacking. In this study, the prevalence and abundance of 20 key oral bacteria was assessed in health and disease and more importantly a closer look was given to the inter-bacterial relationships.

MATERIALS AND METHODS

A blinded microbiological database was analysed in this cross-sectional, retrospective study. The database was constructed based on microbiological analyses of samples from 6308 patients, with gradations of periodontitis (healthy to periodontitis). Data concerning the abundance of 20 oral bacteria and probing pocket depth were provided.

RESULTS

Porphyromonas gingivalis, Tannerella forsythia, Treponema denticola, Eubacterium nodatum, Porphyromonas micra and Porphyromonas intermedia showed a clear increase in abundance and prevalence with increasing pocket depth. Correlation matrices illustrated that almost all microorganisms were in one way correlated to other species and most of these correlations were significant. Several beneficial bacteria showed strong correlations with other beneficial bacteria.

CONCLUSION

Knowledge on bacterial correlations can pave the way for new treatment options focusing on restoring the shifted balance.

TSST-1, enterotoxin and bacteriocin-like substance production by Staphylococcus aureus isolated from foods

The production of Toxic Shock Syndrome Toxin-1 (TSST-1), enterotoxins and bacteriocin-like substances was evaluated in 95 strains of Staphylococcus aureus recovered from raw bovine milk (n=31) and from food samples involved in staphylococcal food poisoning (n=64). Enterotoxigenicity tests with the membrane over agar associated to optimal sensibility plate assays were performed and showed that 96.77% of strains recovered from milk and 95.31% from food samples produced enterotoxins A, B, C, D or TSST-1. Reference strains S. epidermidis, Bacillus cereus, Listeria monocytogenes, Lactobacillus casei, Pseudomonas aeruginosa, S. aureus, Salmonella Typhimurium, Escherichia coli, Enterococcus faecalis and Bacteroides fragilis were used as indicator bacteria in the antagonistic assays, the first five being sensitive to antagonistic substances. Brain heart infusion agar, in pH values ranging from 5.0 to 7.0 in aerobic atmosphere showed to be the optimum condition for antagonistic activity as evaluated with the best producer strains against the most sensitive indicator bacterium, L. monocytogenes. Sensitivity to enzymes confirmed the proteinaceous nature of these substances. Neither bacteriophage activity nor fatty acids were detected and the antagonistic activity was not due to residual chloroform. Results did not establish a positive correlation between the bacteriocinogenic profile and toxigenicity in the tested S. aureus strains.

The effects of stress hormones on growth of selected periodontitis related bacteria

The focus of this study was to examine in vitro the effects of stress hormones (catecholamines: epinephrine, norepinephrine, dopamine and hydrocortisone: cortisol) on the growth of four anaerobic species of periodontitis-related bacteria (Fusobacterium nucleatum, Porphyromonas gingivalis, Prevotella intermedia and Tannerella forsythia) and one facultative anaerobic species (Eikenella corrodens). Bacterial growth was determined by two different methods: fluorescence in situ hybridization (FISH), and the viable count by culture method. To simulate stress, each single strain was grown in a special growth medium with three different concentrations of each hormone, using an anaerobic chamber at 37 °C. Growth of F. nucleatum increased in the presence of all stress hormones. Growth of P. gingivalis was not significantly influenced by any hormone. Growth of P. intermedia and E. corrodens was inhibited by almost all stress hormones tested. Both methods of analysis revealed that the highest concentrations of norepinephrine and cortisol increased the growth of T. forsythia. Different hormones have a different effect on the growth of periodontitis-related bacteria in vitro. It appears that bacterial viability is more strongly influenced than is bacterial metabolic activity. The growth of F. nucleatum particularly and partially of T. forsythia is increased by several stress hormones and may have an additional negative impact on periodontal disease.

Identification of interspecies interactions affecting Porphyromonas gingivalis virulence phenotypes

Background

Periodontitis is recognized as a complex polymicrobial disease, however, the impact of the bacterial interactions among the 700–1,000 different species of the oral microbiota remains poorly understood. We conducted an in vitro screen for oral bacteria that mitigate selected virulence phenotypes of the important periodontal pathogen, Porphyromonas gingivalis.

Method

We isolated and identified oral anaerobic bacteria from subgingival plaque of dental patients. When cocultured with P. gingivalis W83, specific isolates reduced the cytopathogenic effects of P. gingivalis on oral epithelial cells.

Result

In an initial screen of 103 subgingival isolates, we identified 19 distinct strains from nine species of bacteria (including Actinomyces naeslundii, Streptococcus oralis, Streptococcus mitis, and Veilonella dispar) that protect oral epithelial cells from P. gingivalis-induced cytotoxicity. We found that some of these strains inhibited P. gingivalis growth in plate assays through the production of organic acids, whereas some decreased the gingipain activity of P. gingivalis in coculture or mixing experiments.

Conclusion

In summary, we identified 19 strains isolated from human subgingival plaque that interacted with P. gingivalis, resulting in mitigation of its cytotoxicity to oral epithelial cells, inhibition of growth, and/or reduction of gingipain activity. Understanding the mechanisms of interaction between bacteria in the oral microbial community may lead to the development of new probiotic agents and new strategies for interrupting the development of periodontal disease.

Antagonism and synergism in Gardnerella vaginalis strains isolated from women with bacterial vaginosis

Antagonistic and synergistic substances are important for interactions between micro-organisms associated with human body surfaces, either in healthy or in diseased conditions. In the present study, such compounds produced by Gardnerella vaginalis strains isolated from women with bacterial vaginosis (BV) were detected in vitro and the antagonistic ones were partially characterized. Among 11 G. vaginalis strains tested, all showed antagonistic activity against at least one of the 22 indicator bacteria assayed. Interestingly, for some of these strains, antagonism reverted to synergism, favouring one of the indicator strains (Peptostreptococcus anaerobius) when the growth medium was changed. Partial characterization of antagonistic substances suggested a bacteriocin-like chemical nature. Depending on growth conditions, G. vaginalis isolated from women with BV produced antagonistic or synergistic compounds for other bacterial components of the vaginal ecosystem. This is the first report to our knowledge of the production of antagonistic and/or synergistic substances by G. vaginalis. This ability may be a pivotal factor in understanding BV and the ecological role of this bacterium in the vaginal environment.

Bacteriocin production by Shigella sonnei isolated from faeces of children with acute diarrhoea

Shigella is a common agent of diarrhoea, a worldwide major health problem. The bacterium produces bacteriocins; however, the role of these substances as a virulence factor is completely unknown. With the aim to search for colicin production by Shigella sonnei, to evaluate the influence of culture conditions on bacteriocin expression, and to characterize the substance partially, 16 S. sonnei strains isolated from children with diarrhoea were tested for antagonism against members of the intestinal microbiota or agents of diarrhoea. Nine strains exhibited isoantagonism and heteroantagonism against S. flexneri and diarrhoeagenic Escherichia coli. Autoantagonism and antagonism against the intestinal microbiota were not detected. Culture medium and incubation conditions influenced antagonism expression. Antagonism resulting from bacteriophages, low pH, fatty acids, hydrogen peroxide, and chloroform was excluded. The activity of the intracellular fraction obtained with 75% ammonium sulphate was preserved at pH 1.0-11.0, and was found to be reduced by organic solvents and affected by high temperatures and proteases. The antagonistic spectrum and the in vitro conditions for better antagonism expression suggest that the role of colicin in S. sonnei virulence, if any, would be expressed prior to infection, and may regulate population density of enteropathogens by helping in organism transmission.

Interspecies interactions within oral microbial communities

While reductionism has greatly advanced microbiology in the past 400 years, assembly of smaller pieces just could not explain the whole! Modern microbiologists are learning "system thinking" and "holism." Such an approach is changing our understanding of microbial physiology and our ability to diagnose/treat microbial infections. This review uses oral microbial communities as a focal point to describe this new trend. With the common name "dental plaque," oral microbial communities are some of the most complex microbial floras in the human body, consisting of more than 700 different bacterial species. For a very long time, oral microbiologists endeavored to use reductionism to identify the key genes or key pathogens responsible for oral microbial pathogenesis. The limitations of reductionism forced scientists to begin adopting new strategies using emerging concepts such as interspecies interaction, microbial community, biofilms, polymicrobial disease, etc. These new research directions indicate that the whole is much more than the simple sum of its parts, since the interactions between different parts resulted in many new physiological functions which cannot be observed with individual components. This review describes some of these interesting interspecies-interaction scenarios.

Purification and partial characterization of a bacteriocin produced by Eikenella corrodens

AIMS

The purpose of this study was to purify and characterize a bacteriocin produced by Eikenella corrodens A32E2.

METHODS AND RESULTS

Peptostreptococcus anaerobius ATCC27337 was used as indicator strain in antagonistic assays for bacteriocin-producing E. corrodens A32E2. Protein extraction was influenced by pH and buffer composition. The protein was active in the pH range 6-8. Inhibitory activity was lost by both heating and treatment with proteolytic enzymes and decreased with organic solvents. The substance is rather unstable but maintains 100% of its activity after being exposed to acetone and when stored at -70 degrees C. The antagonistic substance was first precipitated by ammonium sulfate and further partially purified by Mono-Q FPLC and C-18 HPLC. Mass spectrometry analysis showed that the molecular mass was 23 625 Da, and the sequence obtained for the N-terminus was: Met-Asn-Phe-Asp-Glu-Lys-Val-Gly-Lys-Val-X-Phe-Lys-Val-Gly-Asp.

CONCLUSIONS

The evidence presented in this study supports the idea that an antagonistic substance produced by E. corrodens A32E2 isolated from a periodontal diseased site is a novel bacteriocin, which we designate corrodecin.

SIGNIFICANCE AND IMPACT OF THE STUDY

We anticipated that corrodecin might play an important role at the periodontal site. This compound could also be attractive in biotechnological applications as an interesting tool for oral ecosystem control.