β-Galactosidase activity and H(2)S production in an experimental oral biofilm

Oral microbiota transplantation for intra-oral halitosis: a feasibility analysis based on an oral microbiota colonization trial in Wistar rats

BACKGROUND

Intra-oral halitosis (IOH) is bad breath produced locally by the mouth in addition to systemic diseases and is one of the main causes of interpersonal communication and psychological disorders in modern society. However, current treatment modalities still only alleviate IOH and do not eradicate it. Therefore, based on the differential performance of oral microecology in IOH patients, we propose a microbiota transplantation treatment aimed at restoring oral microecological balance and analyze its feasibility by oral flora colonization test in Wistar rats.

OBJECTIVE

Saliva flora samples were collected from IOH patients and healthy subjects to analyze the feasibility of oral microbiota transplantation (OMT) for the treatment of IOH by the Wistar rat oral flora colonization test.

METHODS

Seven patients with IOH who visited the First Affiliated Hospital of Xinjiang Medical University from June 2017 to June 2022 with the main complaint of halitosis and three healthy subjects were randomly selected. A Halimeter portable breath detector was used to record breath values and collect saliva flora samples. Sixteen SPF-grade male Wistar rats were housed in the Animal Experiment Center of Xinjiang Medical University and randomly divided into an experimental group (Group E) and a control group (Group C) for the oral flora colonization test. Species composition and associated metabolic analysis of oral flora during the Wistar rat test using 16SrRNA sequencing technology and PICRUSt metabolic analysis. Also, the changes in the breath values of the rats were recorded during the test.

RESULTS

The proportion of Porphyromonas, Fusobacterium, Leptotrichia, and Peptostreptococcus was significantly higher in group E compared to group C after colonization of salivary flora of IOH patients (all P < 0.05), and the abundance with Gemella was zero before colonization, while no colonization was seen in group C after colonization compared to baseline. PICRUSt metabolic analysis also showed significantly enhanced IOH-related metabolic pathways after colonization in group E (all P < 0.05), as well as significantly higher breath values compared to baseline and group C (all P < 0.0001). After colonization by salivary flora from healthy subjects, group E rats showed a decrease in the abundance of associated odor-causing bacteria colonization, a reduction in associated metabolism, and a significant decrease in breath values. In contrast, group C also showed differential changes in flora structure and breath values compared to baseline after salivary flora colonization of IOH patients.

CONCLUSIONS

OMT for IOH is a promising green treatment option, but the influence of environmental factors and individual differences still cannot be ignored.

The Role of the Oral Microbiome in the Development of Diseases

Periodontal disease (PD) is a complex and infectious illness that begins with a disruption of bacterial homeostasis. This disease induces a host inflammatory response, leading to damage of the soft and connective tooth-supporting tissues. Moreover, in advanced cases, it can contribute to tooth loss. The aetiological factors of PDs have been widely researched, but the pathogenesis of PD has still not been totally clarified. There are a number of factors that have an effect on the aetiology and pathogenesis of PD. It is purported that microbiological, genetic susceptibility and lifestyle can determine the development and severity of the disease. The human body’s defence response to the accumulation of plaque and its enzymes is known to be a major factor for PD. The oral cavity is colonised by a characteristic and complex microbiota that grows as diverse biofilms on all mucosal and dental surfaces. The aim of this review was to provide the latest updates in the literature regarding still-existing problems with PD and to highlight the role of the oral microbiome in periodontal health and disease. Better awareness and knowledge of the causes of dysbiosis, environmental risk factors and periodontal therapy can reduce the growing worldwide prevalence of PDs. The promotion of good oral hygiene, limiting smoking, alcohol consumption and exposure to stress and comprehensive treatment to decrease the pathogenicity of oral biofilm can help reduce PD as well as other diseases. Evidence linking disorders of the oral microbiome to various systemic diseases has increased the understanding of the importance of the oral microbiome in regulating many processes in the human body and, thus, its impact on the development of many diseases.

Pre-Disinfection of Poly-Methyl-Methacrylate (PMMA) Reduces Volatile Sulfides Compounds (VSC) Production in Experimental Biofilm In Vitro

Temporary dental crowns and bridges are commonly made of poly-methylmethacrylate (PMMA), a porous material attracting the microbial biofilm associated with malodor production. The purpose of the present study was to test pre-disinfection of PMMA on malodor-related parameters in an experimental oral biofilm. PMMA discs were pre-soaked in anti-malodor disinfecting solutions and controls: (i) Saline, (ii) essential oils (EO), (iii) herbal extracts (HE), and (iv) chlorhexidine (CHX). Following, discs were subjected to a salivary incubation assay and monitored for malodor-producing bacteria within the biofilm using confocal microscopy (CLSM), malodor production (organoleptic scale 0–5), volatile sulfide levels (Halimeter), and salivary protein degradation (SDS-PAGE). Results showed that disinfection solutions were significantly effective in reducing malodor-related parameters (CHX > HE > EO > Saline). Taken together, these results suggest that pre-disinfection may help to reduce malodor production in PMMA temporary dental restorations.

Identification of Salivary Microorganisms and Metabolites Associated with Halitosis

Halitosis is mainly caused by the action of oral microbes. The purpose of this study was to investigate the differences in salivary microbes and metabolites between subjects with and without halitosis. Of the 52 participants, 22 were classified into the halitosis group by the volatile sulfur compound analysis on breath samples. The 16S rRNA gene amplicon sequencing and metabolomics approaches were used to investigate the difference in microbes and metabolites in saliva of the control and halitosis groups. The profiles of microbiota and metabolites were relatively different between the halitosis and control groups. The relative abundances of Prevotella, Alloprevotella, and Megasphaera were significantly higher in the halitosis group. In contrast, the relative abundances of Streptococcus, Rothia, and Haemophilus were considerably higher in the control group. The levels of 5-aminovaleric acid and n-acetylornithine were significantly higher in the halitosis group. The correlation between identified metabolites and microbiota reveals that Alloprevotella and Prevotella might be related to the cadaverine and putrescine pathways that cause halitosis. This study could provide insight into the mechanisms of halitosis.

Salivary β-glucosidase as a direct factor influencing the occurrence of halitosis

β-Glucosidases are enzymes present in all living organisms, playing a pivotal role in diverse biological processes. These enzymes cleave β-glycosidic bonds between carbohydrates, or between a carbohydrate and a non-carbohydrate moiety, which may result in the liberation of volatile aglycones. Released compounds execute diverse physiological roles, while the industry takes advantage of exogenously added β-glucosidases for aroma enrichment during food and beverage production. β-Glucosidase enzymatic activity has been reported in human saliva and given the fact that these enzymes are involved in aroma release, we investigated here the correlation between β-glucosidase activity in human saliva and the occurrence of halitosis. Measurement of salivary enzyme activity of 48 volunteers was performed using p-nitrophenyl-β-d-glucopyranoside as substrate. Each volunteer was clinically evaluated by a dental surgeon and clinical and laboratorial data were statistically analyzed. Gas-chromatography of saliva headspace allowed the analysis of the direct role of exogenous β-glucosidase on aromatic /volatile profile of saliva samples. The data demonstrated a positive correlation between halitosis and enzymatic activity, suggesting that the enzyme exerts a direct role in the occurrence of bad breath. Gas-chromatography analysis demonstrated that exogenously added enzyme led to the alteration of volatile organic content, confirming a direct contribution of β-glucosidase activity on saliva volatile compounds release. Although halitosis is a multifactorial condition, the complete understanding of all governing factors may allow the development of more effective treatment strategies. Such studies may pave the way to the use of β-glucosidase inhibitors for halitosis clinical management.

•

β-Glucosidases are capable of altering the aromatic profile of saliva.

•

Increased salivary β-glucosidase is associated with halitosis.

•

Increased salivary β-glucosidase is associated with dental biofilm.

•

Salivary β-glucosidases are produced by oral microrganisms.

Dynamic Alterations of Oral Microbiota Related to Halitosis in Preschool Children

Objective

This longitudinal study was aimed to evaluate the dynamic shift in oral microbiota during the process of halitosis progression among preschool children.

Methods

The oral examinations, questionnaires and tongue coating specimens were collected at the baseline and 12-month follow-up. All children were oral healthy at the enrollment. At the 12-month follow-up, children who developed halitosis were included to the halitosis group (n = 10). While children who matched the age, gender, kindergarten and without halitosis were included to the control group (n = 10). 16S rRNA gene sequencing was used to reveal the shift of the tongue coating microbiome in these children during the 12- month period with the Human Oral Microbiome Database.

Results

A remarkable shift in relative abundance of specific bacteria was observed prior to halitosis development. The principal coordinates and alpha diversity analyses revealed different shifting patterns of halitosis and the healthy participants’ microbiome structures and bacterial diversity over the 12-month follow-up. Both groups showed variable microbiota community structures before the onset of halitosis. Halitosis-enriched species Prevotella melaninogenica, Actinomyces sp._HMT_180 and Saccharibacteria TM7_G-1_bacterium_HMT_352 were finally selected as biomarkers in the halitosis-onset prediction model after screening, with a prediction accuracy of 91.7%.

Conclusions

The microbiome composition and relative abundance of the tongue coatings in the halitosis and control groups remarkably differed, even prior to the onset of the clinical manifestations of halitosis. The halitosis prediction model constructed on the basis of tongue coating microbiome biomarkers indicated the microbial shifts before the halitosis onset. Therefore, this can be considered for the timely detection and intervention of halitosis in children.

Microbiome variations in preschool children with halitosis

OBJECTIVE

To assess the bacterial characteristics associated with intra-oral halitosis among Chinese preschool children.

METHODS

An epidemiological study was conducted among 273 preschool children (aged 3-4 years) in Shanghai, China, followed by the collection of 16 samples from the tongue coating of caries-free healthy and halitosis participants. The characterization of associated microbial communities was performed using 16S rRNA gene sequencing on the MiSeq.

RESULTS

Halitosis was observed in 13.2% of the preschool children. No significant difference in terms of microbial diversity (p > .05) was detected in the control and halitosis groups. The dominant bacterial genera observed in both groups included Prevotella, Veillonella, Streptococcus, Neisseria, Actinomyces, Haemophilus, and Leptotrichia. The relative proportions of thirteen species (including Leptotrichia sp. HMT_417, Prevotella Pallens, and Alloprevotella rava) were significantly higher in the halitosis group compared with the control group, whereas the distribution of seventeen species from genera Streptococcus, Gemella, and Kingella showed a higher abundance in the control group. Further investigation of interactions among species demonstrated obvious differences in two groups, indicating that various microorganisms interact to produce halitosis in preschool children.

CONCLUSIONS

Overall, halitosis is associated with multi-microbial mutual interactions. The oral flora microorganisms may exert potentiating or inhibiting effects on each other.

The tongue microbiome in healthy subjects and patients with intra-oral halitosis

Intra-oral halitosis (IOH) is an unpleasant odor emanating from the oral cavity. It is thought that the microbiota of the dorsal tongue coating plays a crucial role in this condition. The aim of the study was to investigate the composition of the tongue microbiome in subjects with and without IOH. A total of 26 subjects, 16 IOH patients and 10 healthy subjects were recruited based on their organoleptic score and volatile sulfur compound (VSC) measurements. The composition of the tongue microbiome was studied using the 16s amplicon sequencing of the V3-V4 hyper variable region with an Illumina MiSeq. The sequenced data were analyzed using QIIME, and the sequences obtained were distributed across 7 phyla, 27 genera and 825 operational taxonomic units (OTUs). At a higher taxon level, TM7 was associated with IOH patients whereas Gemellaceae was significantly abundant in the healthy subjects. At OTU level, we found several significant OTUs that differentiated the IOH patients from the controls. These included Aggregatibacter (OTU id 4335776), Aggregatibacter segnis (A. segnis), Campylobacter, Capnocytophaga, Clostridiales, Dialister, Leptotrichia, Parvimonas, Peptostreptococcus, Peptococcus, Prevotella, Selenomonas, SR1, Tannerella, TM7-3 and Treponema in the IOH group. In the control group, Aggregatibacter (OTU id 4363066), Haemophilus, Haemophilus parainfluenza (H. parainfluenza), Moryella, Oribacterium, Prevotella, several Streptococcus, Rothia dentocariosa (R. dentocariosa) and OTU from Gemellaceae were significantly abundant. Based on our observation, it was concluded that the bacterial qualitative composition of the IOH and the control group was almost the same, except for the few above-mentioned bacterial species and genera.

Zinc enhances the phototoxic effect of blue light against malodour-producing bacteria in an experimental oral biofilm

Oral malodour is thought to be caused mainly by the production of volatile sulfide compounds (VSCs) by anaerobic Gram-negative oral bacteria. Previous studies have shown that these bacteria are susceptible to blue light (400-500 nm wavelength). In the present study, we tested the effect of blue light in the presence of zinc, erythrosine B or both on malodour production in an experimental oral biofilm. Biofilms were exposed to a plasma-arc light source for 30, 60 and 120 s (equal to energy fluxes of 41, 82 and 164 J cm(-2), respectively) with or without the addition of zinc acetate, erythrosine B or both. After the light exposure, biofilm samples were examined for malodour production (by an odour judge) and VSC production (with a Halimeter), and VSC-producing bacteria were quantified using a microscopy-based sulfide assay (MSA) and in situ confocal laser scanning microscopy (CLSM). Results showed that exposing experimental oral biofilm to both blue light and zinc reduced malodour production, which coincided with a reduction in VSC-producing bacteria in the biofilm. These results suggest that zinc enhances the phototoxicity of blue light against malodour-producing bacteria.

In vitro CPC retention and VSC adsorption by IPM oil droplets: possible mechanisms of action of a two phase mouthwash

Two phase oil-water mouthwash has been previously shown to efficiently bind oral microorganisms, relying on their cell surface hydrophobicity. The aim of the present in vitro study was to test the cetylpyridinium chloride (CPC) retention and volatile sulfide compounds (VSCs) adsorption abilities of the oil droplets created by mixing of a two phase oil-water solution. VSC adsorption was assayed using a salivary incubation assay and garlic powder solutions, and demonstrated using microscopic sulfide assay. CPC retention was assayed by kinetic and endpoint measurement of Streptococcus salivarius outgrowth using microplate (ELISA) reader. Results showed that the isopropyl myristate (IPM) oil droplets in the two phase solutions were able to adsorb 68-80% of VSCs. CPC at a concentration of 0.05% was most affectively retained by the oil droplets showing a significantly increase in residual antibacterial activity against Streptococcus salivarius. These results taken together, suggests that VSC adsorption and CPC retention by IPM oil droplets may be two additional mechanisms in the activity of the two phase mouthwash formulation.

Relationship between the β-galactosidase activity in saliva and parameters associated with oral malodor

Volatile sulfur compounds (VSCs) are produced by enzymes capable of transforming S-amino acids to corresponding sulfides. Protein degradation by periodontopathogens plays an important role in this process, and the proteolysis of glycoproteins depends on the initial removal of the carbohydrate side chains. In the present report, we tested the relationship between the β-galactosidase activity in saliva and parameters that influence oral malodor, including daily habits and oral conditions. The prevalence of periodontopathic bacteria was also examined. Forty-nine saliva samples were collected from halitosis patients. Patients were examined for breath odor and other associated parameters. Their breath odor was assessed using an organoleptic test, a portable sulfide monitor and gas chromatography. The presence of periodontopathic bacteria in the saliva was also examined. β-galactosidase activity was measured with the chromogenic substrates 5-bromo-4-chloro-3-indoyl-β-d-galactopyranoside and isopropyl-β-d-thiogalactopyranoside. β-galactosidase activity was positively correlated with malodor strength (organoleptic score, portable sulfide monitor score and VSC concentrations). Enzyme activity was also correlated with the degree of observable tongue coating. However, it showed no relationship with periodontal condition, saliva flow, tooth decay, unfitted restorations or the color of any tongue coating. While there was no relationship with Porphyromonas gingivalis and Treponema denticola, there was a negative correlation with Prevotella intermedia. These results indicate that β-galactosidase activity plays an important role in malodor production. Interestingly, the activity of this enzyme was not related to the presence of periodontopathic bacteria, which are the main malodor-producing organisms. The results obtained here may have been associated with physiologic halitosis, which is not necessarily associated with oral problems or with periodontopathic bacteria.