Identification of disulphide stress-responsive extracytoplasmic function sigma factors in Rothia mucilaginosa

Biofilm disruption and bactericidal activity of aqueous ozone coupled with ultrasonic dental scaling

Background

The COVID-19 pandemic has heightened the awareness of a common hazard encountered in the dental clinic: aerosol transmission of pathogens. Treatment of sources of infection before or during dental procedures is one means of decreasing pathogen load and aerosol transmission.

Methods

An ultrasonic scaler supplied with aqueous ozone was used to examine the effect of its viability on planktonic cultures and biofilms formed by 2 model bacteria: Rothia mucilaginosa and Escherichia coli.

Results

Both organisms showed susceptibility to aqueous ozone alone (97% and 99.5% lethality, respectively). When combined with manual scaling using an ultrasonic scaler, a greater than 99% reduction in colony-forming units (CFUs)/mL could be reached with an aqueous ozone concentration of approximately 2 mg/L (R. mucilaginosa) or 0.75 mg/L (E. coli) after 5 through 6 seconds of scaling.

Conclusions

Aqueous ozone coupled with ultrasonic scaling exhibited a higher efficiency of microbial kill than either method used alone. Both gram-positive and gram-negative species were affected by this treatment. Studies on other oral microbiota constituents, including fungi and viruses, will provide information on the efficacy of this method on a greater biological scale. Studies to verify concomitant reduction of microbial load in dispersed aerosols in clinical settings should be completed to support practical applications of this treatment.

A novel catalytic heme cofactor in SfmD with a single thioether bond and a bis-His ligand set revealed by a de novo crystal structural and spectroscopic study

SfmD is a heme-dependent enzyme in the biosynthetic pathway of saframycin A. Here, we present a 1.78 Å resolution de novo crystal structure of SfmD, which unveils a novel heme cofactor attached to the protein with an unusual Hx n HxxxC motif (n ∼ 38). This heme cofactor is unique in two respects. It contains a single thioether bond in a cysteine-vinyl link with Cys317, and the ferric heme has two axial protein ligands, i.e., His274 and His313. We demonstrated that SfmD heme is catalytically active and can utilize dioxygen and ascorbate for a single-oxygen insertion into 3-methyl-l-tyrosine. Catalytic assays using ascorbate derivatives revealed the functional groups of ascorbate essential to its function as a cosubstrate. Abolishing the thioether linkage through mutation of Cys317 resulted in catalytically inactive SfmD variants. EPR and optical data revealed that the heme center undergoes a substantial conformational change with one axial histidine ligand dissociating from the iron ion in response to substrate 3-methyl-l-tyrosine binding or chemical reduction by a reducing agent, such as the cosubstrate ascorbate. The labile axial ligand was identified as His274 through redox-linked structural determinations. Together, identifying an unusual heme cofactor with a previously unknown heme-binding motif for a monooxygenase activity and the structural similarity of SfmD to the members of the heme-based tryptophan dioxygenase superfamily will broaden understanding of heme chemistry.

Complete Genome Sequence of Rothia mucilaginosa Strain NUM-Rm6536, Isolated from a Human Oral Cavity

Here, we present the complete genome sequence of Rothia mucilaginosa NUM-Rm6536, a strain isolated from the tongue plaque of a healthy human adult. This strain is amenable to genetic manipulation by transformation and so provides a useful foundation for more detailed investigation of this species.

Supplementary sampling of obturation materials enhances microbial analysis of endodontic treatment failures: a proof of principle study

OBJECTIVES

Root canal treatment failures often correlate with persistent biomaterial-associated endodontic infections. The aim of the present study was to assess the impact of endodontic obturation material sampling from root canals with posttreatment apical periodontitis on improving standard study protocols.

MATERIALS AND METHODS

Samples from previously filled root canals and their corresponding endodontic filling materials were obtained from five root-filled teeth with posttreatment periradicular lesions. After cultivation, the isolated microorganisms were quantified and biochemically identified. Moreover, clone libraries were constructed after the amplification of bacterial 16S ribosomal DNA (rDNA) from the same samples. DNA from selected clones was sequenced to identify microbial species. Transmission electron microscopy (TEM) aided visualization of the detected bacteria.

RESULTS

Overall, 22 taxa of the phyla Firmicutes, Actinobacteria, and Bacteroidetes were detected in both obturation and root canal samples by culture-dependent and culture-independent methods. Root canal fillings sheltered 17 species (3.30-7.50 × 10(3) CFU/ml). Of these, nine were detected solely in the retrieved obturation materials. The reinfected root canals harbored 13 taxa (3.48-7.36 × 10(3) CFU/ml). Obligate and facultative anaerobic bacteria prevailed. The number of different species ranged from 1 to 5 within a single sample. Fungi were not detected.

CONCLUSIONS

Bacteria can colonize both root canals and endodontic fillings in vivo.

CLINICAL RELEVANCE

Integrating the sampling of obturation materials with standard root canal sample collection offers a clearer insight into the actual microbial flora of reinfected root canals and improves the study protocols of secondary/persistent endodontic infections.