Pathogenicity of exopolysaccharide-producing Actinomyces oris isolated from an apical abscess lesion

Complete Genome Sequence of Actinomyces oris Strain K20, Isolated from an Oral Apical Lesion

Actinomyces oris strain K20 was isolated from oral apical lesions. Here, we report the complete circular genome sequence of this strain, obtained by means of hybrid assembly using two next-generation sequencing datasets. The strain has a 3.1-Mb genome with 2,636 coding sequences.

D-arginine Enhances the Effect of Alpha-Amylase on Disassembling Actinomyces viscosus Biofilm

Peri-implantitis is the leading cause of dental implant failure, initially raised by biofilm accumulation on the implant surface. During the development of biofilm, Actinomyces viscosus (A. viscosus) plays a pivotal role in initial attachment as well as the bacterial coaggregation of multispecies pathogens. Hence, eliminating the A. viscosus-associated biofilm is fundamental for the regeneration of the lost bone around implants. Whereas clinical evidence indicated that antimicrobials and debridement did not show significant effects on the decontamination of biofilm on the implant surface. In this study, alpha-amylase was investigated for its effects on disassembling A. viscosus biofilm. Then, in order to substantially disperse biofilm under biosafety concentration, D-arginine was employed to appraise its enhancing effects on alpha-amylase. In addition, molecular dynamics simulations and molecular docking were conducted to elucidate the mechanism of D-arginine enhancing alpha-amylase. 0.1–0.5% alpha-amylase showed significant effects on disassembling A. viscosus biofilm, with definite cytotoxicity toward MC3T3-E1 cells meanwhile. Intriguingly, 8 mM D-arginine drastically enhanced the eradication of A. viscosus biofilm biomass by 0.01% alpha-amylase with biosafety in 30 min. The exopolysaccharides of biofilm were also thoroughly hydrolyzed by 0.01% alpha-amylase with 8 mM D-arginine. The biofilm thickness and integrity were disrupted, and the exopolysaccharides among the extracellular matrix were elusive. Molecular dynamics simulations showed that with the hydrogen bonding of D-arginine to the catalytic triad and calcium-binding regions of alpha-amylase, the atom fluctuation of the structure was attenuated. The distances between catalytic triad were shortened, and the calcium-binding regions became more stable. Molecular docking scores revealed that D-arginine facilitated the maltotetraose binding process of alpha-amylase. In conclusion, these results demonstrate that D-arginine enhances the disassembly effects of alpha-amylase on A. viscosus biofilm through potentiating the catalytic triad and stabilizing the calcium-binding regions, thus providing a novel strategy for the decontamination of biofilm contaminated implant surface.

Identification of Dominant Bacteria Isolated From Periodontal Abscesses

Aim:

Various methods investigating the bacterial content causing periodontal abscesses have been applied in studies conducted until today. However, these studies have focused on periodontopathogens. Our study was carried out to research whether different pathogens other than the known periodontopathogens are present in periodontal abscess formation. Therefore, dominant bacterial samples obtained from the periodontal abscess content using the culture-dependent method were identified by 16S rDNA sequencing.

Materials and Methods:

Samples were obtained using a syringe or a periopaper from periodontal abscesses of 20 volunteers who met the research criteria. The three different bacterial colonies that were observed most intensely in each sample were selected and purified, and the isolates obtained were kept until the next characterization. Genomic DNA was isolated from each isolate; 16S rRNA genes were amplified by polymerase chain reaction and identified using DNA sequencing analyses.

Results:

As a result of culture-dependent methods, bacterial species belonging to Streptococcus, Staphylococcus, Neisseria, Actinomyces, Morococcus, Moraxella, and Enterococcus genera were isolated from a total of 60 bacterial isolates, three of which were the most densely growing colonies from each periodontal abscess sample.

Conclusion:

In our study, most of the bacterial species detected were identified for the first time in the bacterial content of periodontal abscesses. In some previously done studies, most of these bacteria species were shown to cause abscesses in different parts of the body. It was concluded that further studies are needed to determine the number and proportion of these bacteria species in total bacterial content to evaluate whether they cause periodontal abscesses.

Biochemical characterization of extracellular polymeric substances from endodontic biofilms

Apical periodontitis is frequently associated with the presence of bacteria biofilm, which has an indisputable impact on the prognosis of endodontic therapy due to the high resistance to adverse environmental conditions, chemicals, and antibiotic therapy that characterize bacteria within biofilm. The biofilm matrix acts as a protective shield over the encased microorganisms. The aim of this investigation was to identify the main biochemical components of biofilm matrix from endodontic mono- and dual-species biofilms. Enterococcus faecalis and Actinomyces naeslundii were cultured as mono- and dual-species biofilms for 14 days. Crude extracellular polymeric substances (EPSs) from biofilm matrices were extracted using chemical and physical methods. High-performance liquid chromatography, gas chromatography, and mass spectrometry were used to determine the carbohydrate, protein, and fatty acid components. Chemical analysis of the biofilm matrices revealed that they were mainly composed of stachyose, maltose, and mannose carbohydrates. The protein profile in all biofilm samples showed abundant oxidoreductases and chaperone proteins and some virulence- associated proteins mainly located in the membrane surface. High percentages of saturated and monounsaturated fatty acids were identified in all biofilm matrices, with a major prevalence of palmitic, stearic, and oleic acids. Based on the results, it was possible to obtain for the first time a general overview of the biochemical profile of endodontic biofilm matrices.

Prevalence of Actinomyces spp. in patients with chronic periodontitis

This study investigated the prevalence of Actinomyces spp. in shallow, deep and very deep pockets of patients with chronic periodontitis compared to healthy controls and correlated the results with clinical status. Twenty patients with chronic periodontitis and 15 healthy subjects were enrolled in this study. Clinical indices were recorded in a six-point measurement per tooth. From each patient samples of supra and subgingival plaque were taken separately from teeth with shallow, deep and very deep pockets. Samples of supragingival plaque and sulcular microflora were collected from the healthy subjects. All the samples were cultivated on different media at 37̊C in an anaerobic atmosphere for 7 days. All the suspect colonies were identified using a rapid ID 32 A system (bioMèrieux) and MALDI-TOF-MS analysis using an Autoflex II Instrument (Bruker Daltonics) together with in house developed identification software and a reference spectra database. A total of 977 strains were identified as Actinomyces. Actinomyces naeslundii/oris/johnsonii (430 isolates) was the most prevalent species and was found in all patients and in almost all of the healthy subjects. Significant differences (p=0.003) between the groups were found for Actinomyces odontolyticus/meyeri and Actinomyces israelii which were associated with periodontitis patients. Actinomyces dentalis was found in higher percentage (p=0.015) in the periodontitis group. Actinomyces gerencseriae and Actinomyces massiliensis were significantly more often found supragingivally than subgingivally (p=0.004, p=0.022, respectively) in the periodontitis group. Whether some Actinomyces species, definitely important plaque formers, are actively involved in the pathogenicity of chronic periodontitis needs further investigation.

Identification of the genes involved in the biofilm-like structures on actinomyces oris K20, a clinical isolate from an apical lesion

INTRODUCTION

Although the production of biofilm is thought to be crucial in the pathogenesis of abscess formations caused by oral resident microorganisms, the particular mechanisms are still unknown. The aim of this study was to identify gene(s) responsible for maintaining the cell surface-associated meshwork-like structures, which are found in some biofilm-producing bacteria, in a clinical isolate of Actinomyces oris K20.

METHODS

Random insertional mutagenesis by using transposon EZ-Tn5 was performed against the strain K20. Transposon insertion mutants were screened by scanning electron microscopy for the absence of cell surface-associated meshwork-like structures. The disrupted genes by the transposon insertion were determined by direct genome sequencing with the transposon-end primers.

RESULTS

Five mutants without the meshwork-like structures were identified from 175 mutants. Sequencing of flanking regions of transposon insertion revealed that 3 mutants had a gene encoded polysaccharide deacetylase, Spo0J containing ParB-like nuclease domain, and hypothetical protein, respectively. The other 2 mutants had an insertion in a noncoding region and an unidentified region, respectively.

CONCLUSIONS

Our findings indicated that these genes might be involved in the formation of meshwork-like structures on Actinomyces oris K20.