Association of oral streptococci community dynamics with severe early childhood caries as assessed by PCR-denaturing gradient gel electrophoresis targeting the rnpB gene

Development of novel broad-range pan-genus PCR assays for the detection of Tropheryma species

Introduction. Tropheryma whipplei is responsible for the classical Whipple's disease. Recently, a new Tropheryma species was described in a Belgian immunocompromised patient with pleuritis.Gap Statement. There is currently no specific molecular diagnostic test detecting other Tropheryma species than Tropheryma whipplei.Aim. To develop and validate two broad-range pan-Tropheryma genus PCRs detecting both T. whipplei and new Tropheryma species.Methodology. From shotgun sequencing data of the lung tissue biopsy of the Belgian subject, we designed two PCRs targeting the 23S rRNA and rnpB genes. Prospectively, requests for T. whipplei PCR were tested with T. whipplei-specific PCRs and the two Tropheryma broad-range PCRs from January 2019 to November 2022.Results. In total, 2605 samples were tested using both the pan-Tropheryma 23S rRNA PCR and the T. whipplei-specific PCR. In addition, 833 of the 2605 samples were also tested using the pan-Tropheryma rnpB PCRs. Sensitivity was 78.8% and 79.7% for 23S rRNA and rnpB PCRs, as compared with the species-specific T. whipplei PCR. Specificity was 99.9% and 99.7% for the 23S rRNA and the rnpB PCRs, respectively. We identified a patient whose bronchoalveolar lavage tested positive with the two broad-range PCRs with >105 copies ml-1. Specific T. whipplei PCRs were negative. Known for panuveitis, this 49-year-old male presented with an eye inflammation recurrence, and a CT scan showed multiple mediastino-hilar necrotic adenopathies. Doxycyclin (1 year), hydroxychloroquin (1 year) and co-trimoxazol (1 month) treatments led to a favourable outcome.Conclusion. Specific T. whipplei PCR exhibited better sensitivity than the pan-Tropheryma PCRs. However, both broad-range pan-Tropheryma PCRs demonstrated excellent specificity and were pivotal to identifying a new probable case of Tropheryma infection due to another species-level lineage.

vicR overexpression in Streptococcus mutans causes aggregation and affects interspecies competition

Streptococcus mutans is considered to be a major causative agent of dental caries. VicRK is a two-component signal transduction system (TCSTS) of S. mutans, which can regulate the virulence of S. mutans, such as biofilm formation, exopolysaccharide production, acid production, and acid resistance. Meanwhile, it can also regulate the production of mutacins (nlmC) through the TCSTS ComDE. In this study, we found that the vicR-overexpressing strain was more likely to aggregate to form cell clusters, leading to the formation of abnormal biofilm; the overexpression of vicR increased the length of the chain of S. mutans. Furthermore, the expression of the mutacins in the vicR overexpression strain was increased under aerobic conditions. Compared with the control strain and the parental strain, the vicR overexpression strain was more competitive against Streptococcus gordonii. But there was no significant difference against Streptococcus sanguinis. In clinical strains, the expression level of vicR was positively correlated with their competitive ability against S. gordonii. Transcriptional profiling revealed 24 significantly upregulated genes in the vicR-overexpressing strain, including nlmA, nlmB, nlmC, and nlmD encoding mutacins. Electrophoretic mobility shift assays and DNase I footprinting assays confirmed that VicR can directly bind to the promoter sequence of nlmD. Taken together, our findings further demonstrate that VicRK, an important TCSTS of S. mutans, is involved in S. mutans cell morphology and biofilm formation. VicRK regulates the production of more mutacins in S. mutans in response to oxygen stimulation. VicR can bind to the promoter sequence of nlmD, thereby directly regulating the production of mutacins NlmD.

Genomic and phenotypic characterization of Streptococcus mutans isolates suggests key gene clusters in regulating its interaction with Streptococcus gordonii

Streptococcus mutans (S. mutans) is one of the primary pathogens responsible for dental caries. Streptococcus gordonii (S. gordonii) is one of the early colonizers of dental plaque and can compete with S. mutans for growth. In the present analysis, we explored key target genes against S. gordonii in S. mutans using 80 S. mutans clinical isolates with varying capabilities against S. gordonii. A principal coordinate analysis revealed significant genetic diversity differences between antagonistic and non-antagonistic groups. Genomic comparisons revealed 33 and 61 genes that were, respectively, positively and negatively correlated with S. mutans against S. gordonii, with RNA-sequencing (RNA-seq) highlighting 11 and 43 genes that were, respectively, upregulated and downregulated in the antagonistic group. Through a combination of these results and antiSMASH analysis, we selected 16 genes for qRT-PCR validation in which the expression levels of SMU_137 (malate dehydrogenase, mleS), SMU_138 (malate permease, mleP), SMU_139 (oxalate decarboxylase, oxdC), and SMU_140 (glutathione reductase) were consistent with RNA-seq results. SMU_1315c-1317c (SMU_1315c transport-related gene) and SMU_1908c-1909c were, respectively, downregulated and upregulated in the antagonistic group. The expression patterns of adjacent genes were closely related, with correlation coefficient values greater than 0.9. These data reveal new targets (SMU_137–140, SMU_1315c-1317c, and SMU_1908c-1909c) for investigating the critical gene clusters against S. gordonii in S. mutans clinical isolates.

[Association of sepM gene mutation with mutacin Ⅳ production by Streptococcus mutans]

OBJECTIVE

To investigate the types of sepM gene mutations and their distribution in clinical isolates of Streptococcus mutans (S. mutans) and explore the association of sepM gene mutation with the capacity of mutacin Ⅳ production by S. mutans.

OBJECTIVE

We assessed the capacity of mutacin Ⅳ production in 80 clinical isolates of S. mutans using an inhibition zone assay. The minimum spanning tree and phylogenetic tree of these isolates were constructed using core genome multilocus sequence typing and maximum likelihood method, respectively. GeneMarkS software was used to predict the coding genes of these isolates, and the predicted genes were blasted against the sepM gene sequence of the reference genome UA159 to determine sepM gene mutations and their distribution characteristics in the clinical isolates. The mutation types affecting mutacin Ⅳ production were identified by analyzing the differentially distributed mutations between mutacin Ⅳ-producing isolates and mutacin Ⅳ-free isolates and by comparing the inhibition zones between isolates with sepM gene mutations and those without mutations.

OBJECTIVE

Among the 80 clinical isolates of S. mutans, 25 isolates were capable of mutacin Ⅳ production and 55 did not produce mutacin Ⅳ. The minimum spanning tree showed that the allelic differences were less among the mutacin Ⅳproducing isolates than among the mutacin Ⅳ-free isolates, and the origins of the mutacin Ⅳ-producing isolates were similar. We identified a total of 34 single base mutations in the 80 clinical isolates, and among them, C31T (P=0.001), G533A (P < 0.001), C756T (P=0.025), and C1036T (P=0.003) showed significant differential distributions between the mutacin Ⅳ-producing and mutacin Ⅳ-free isolates. These differentially distributed mutations were positively correlated with the capacity of mutacin Ⅳ production of the bacteria.

OBJECTIVE

sepM gene mutations that affect the capacity of mutacin Ⅳ production are present in the clinical strains of S. mutans.

Insight into the Effect of Small RNA srn225147 on Mutacin IV in Streptococcus mutans

Streptococcus mutans (S. mutans) is a serious microbe causing dental caries. Mutacin IV is an effective bacteriocin produced by S. mutans to antagonize numerous non-mutans streptococcal species. However, the posttranscriptional regulation of mutacin IV remains unclear. This study aimed to analyze the effect of small RNA srn225147 on mutacin IV. The functional prediction suggested that srn225147 is involved in the production of mutacin IV, an important secondary metabolite. According to RNAhybrid and RNAPredator prediction, the mutacin IV formation-associated gene comD is a target of srn225147. We further analyzed the roles of srn225147 and comD in 20 S. mutans clinical strains with high production of mutacin IV (High-IV group) and lacking mutacin IV (None-IV group). Levels of comD expression were significantly higher in the High-IV group, whereas the Non-IV group showed relatively higher expression of srn225147, with a negative correlation observed between srn225147 and comD. Moreover, compared to the mimic negative control (NC) group, comD expression was decreased at 400-fold srn225147 overexpression but increased at approximately 1400-fold overexpression. Although the production of mutacin IV in the 1400-fold change srn225147 mimic group was larger than that in the 400-fold change mimic group, there was no significant difference in the production of mutacin IV between the srn225147 mimic group and mimic NC group. These results indicate that srn225147 has a two-way regulation effect on the expression of comD but that its regulation in the production of mutacin IV is weak.

Salivary antioxidant capacity of children with severe early childhood caries before and after complete dental rehabilitation

OBJECTIVE

There is a need to determine whether total antioxidant capacity (TAC) in severe early childhood caries (S-ECC) is an indicator of inflammatory response to the lesion or a marker of the disease. This study compared TAC levels in children with ECC before and after dental treatment and compared the results with those of caries-free children.

DESIGN

Prospective study.

SETTING

A teaching hospital.

PATIENT SELECTION

Salivary samples were obtained from 20 children aged 5 years and diagnosed with S-ECC, and 20 age- and sex-matched controls.

INTERVENTION DETAILS

Complete dental rehabilitation under general anesthesia was performed on the children with S-ECC, and follow-up salivary samples were obtained one week and three months postoperatively. TAC was measured using a commercially available Oxygen Radical Absorbance Antioxidant Assay measurement kit (Zen-Bio ORAC™, AMS Biotechnology, Abington, UK).

OUTCOME MEASURES

Differences between children with and without dental caries were tested using the Mann-Whitney U test; differences before and after dental treatment were analyzed using Friedman test followed by Wilcoxon sign-rank test with Bonferroni correction to compensate for multiple comparisons.

RESULTS

Median TAC (1.54 mcg/L, CI 1.15-1.92) of the control group was significantly lower than that of the treated group prior to treatment (p = 0.003). Treatment of the dental lesions significantly reduced TAC of the treated group, and no significant differences were observed between the test and control groups at either one week (p = 0.076) recall or three-month recall (p = 0.096). TAC in children posttreatment was significantly reduced compared to their pretreatment values (p < 0.001).

CONCLUSION

Total antioxidant capacity in the saliva of children with severe early childhood caries undergoes significant reduction following treatment of the carious lesions.