The oral microbiome and its association with chronic and systemic disease in a South African population

Abstract

Background: The oral microbiome is a complex system that harbors a personalized microbiome. The main function is to maintain health and by doing so they interact with each other and also the human host. If any disruption occurs it will cause an ecological shift in the oral microbiota which will allow pathogens in the form of biofilms to manifest and cause oral diseases. Severe forms of oral disease may progress into systemic diseases such as Diabetes Mellites (DM), Cardiovascular disease (CVD), and Metabolic syndrome (MetS). As the relationship between the human microbiome and health becomes more apparent, more researchers are investigating these relationships as it is clear from previous research that disruptions of the oral microbiome can initiate an abnormal inflammatory response leading to periodontitis and systemic disease. However, information on the causes and changes in the oral microbiota of the oral cavity in individuals with diabetes and MetS is limited. Therefore this project aimed to investigate and characterise the oral plaque samples, using 16s rDNA, in individuals who smoked, are Diabetic, and who had MetS. Methods: Dental assessment was conducted according to guidelines from the World Health Organization (WHO., 2016) and the Community Periodontal Index. Each tooth was probed for bleeding on probing (BOP) and was recorded as presence or absence of bleeding after gentle periodontal probing around each tooth circumference. For pocket depth (PD), each tooth was probed in its whole circumference, and the highest score was recorded. Plaque samples were collected using the wood toothpick method. The device was inserted in the subgingival crevice between the maxillary second premolar and the first upper molar, and 4 toothpick samples were collected from both sides of the mouth and stored separately. Plaque samples with visible presence of blood were not included in this study. The samples were immediately stored at –80 °C until DNA isolation and purification. DNA was extracted as per manufacturer instruction from each pooled toothpick using a DNA extraction kit from Zymo Quick–DNA Fungal/Bacterial Miniprep Kit (Zymo Research). Next-generation sequencing (NGS) was conducted on the 128 plaque samples using the Ion 530 Chip where massive Massively parallel sequencing was performed on the Ion S5 Gene Studio with the Ion S5 IonTorrent. Results: When analysing the oral microbiota in patients across glycaemic status more than two-thirds of all subjects (63.4%, n = 81) had bleeding on probing. Although this was nonsignificantly distributed among the glycemic statuses, 24 (75%) subjects with known diabetes and treatment had gingival bleeding. Periodontal PD ≥4 mm was observed in 75 (58.6%) individuals, and these included 7 (5.5%) with PD ≥6 mm. The most abundant genera observed When oral microbiota analyses were performed patients across glycaemic status genera Fusobacteria and Actinobacteria were significantly enriched and Proteobacteria less enriched in subjects with DM and prediabetes. In those with gingival bleeding, Bacteroidetes were significantly more enriched. As for patients with DM and gingival bleeding reduced abundance was seen in genera Actinobacteria genera. Furthermore, in the smoking group, the oral microbiome was significantly enriched with gram-negative anaerobes. When comparing the oral microbiota within smokers and non-smokers a reduction in the abundance of the phyla Actinobacteria in smokers was observed. Genera Fusobacterium and Campylobacter were found in higher abundance, while genera Leptotrichia, Actinomyces, Corynebacterium, and Lautropia were found in decrease abundance were observed in smokers. As for the comparison of subjects with MetS and without MetS a significant increase in gram-positive aerobic and anaerobic microbiota was observed in those with MetS. Also in MetS subjects, the abundant genera present was Actinomyces, Corynebacterium, and Fusobacterium. Conclusion: Our findings, therefore, concluded that the key to maintaining health is to maintain a well-balanced oral microbiome. Any disruption in the ecosystem due to risk factors such as smoking and other environmental factors will result in a pathogen-rich oral cavity which may provide entry of these oral bacteria into the surrounding tissue resulting in periodontal disease. This is achieved by changing the relationship between microbes and host, by increasing the relative abundance and the acquisition of virulent factors promoting oral disease. As suggested by literature the oral cavity is the primary gateway to the body and severe cases of periodontal disease may promote systemic diseases such as DM, CVD, and MetS.