[Latest Findings on Polyketides/Non-ribosomal Peptides That Are Secondary Metabolites of Streptococcus mutans]

Dental caries is a chronic infectious disease that occurs in the hard tissue of teeth under the influence of multiple factors, among which bacteria being a key factor. Streptococcus mutans ( S. mutans) is considered a major pathogen that causes caries. Secondary metabolites, including bacteriocins and polyketides/non-ribosomal peptides, are a class of small-molecule compounds synthesized by S. mutans. To date, polyketides/non-ribosomal peptides identified in S. mutans include mutanobactin, mutanocyclin, and mutanofactin, which are synthesized by the mub, muc, and muf biosynthetic gene clusters, respectively. These polyketides/non-ribosomal peptides play important roles in bacterial inter-species competition, oxidative stress, and biofilm formation. In this review, we provided an overview of the synthesis, function and regulation of three polyketides/non-ribosomal peptides of S. mutans, including mutanobactin, mutanocyclin, and mutanofactin, aiming to provide new insights into the cariogenic mechanism of S. mutans and to promote the better management of dental caries.

[Mechanisms and Management of COVID-19-Associated Taste Disorders]

The taste buds in the human tongue contain specialized cells that generate taste signals when they are stimulated. These signals are then transmitted to the central nervous system, allowing the human body to distinguish nutritious substances from toxic or harmful ones. This process is critical to the survival of humans and other mammals. A number of studies have shown that dysgeusia, or taste disorder, is a common complication of coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, which can severely affect patients' nutritional intake and quality of life. Based on the physiological process of taste perception, the direct causes of dysgeusia include dysfunction of taste receptors and damage to the taste nervous system, while indirect causes include genetic factors, aging-related changes, bacterial and viral infections, and cancer treatments such as radiotherapy and chemotherapy. The pathogenic factors of dysgeusia are complicated, further research is needed to fully understand the underlying mechanisms, and some of the reported findings and conclusions still need further validation. All these form a great challenge for clinical diagnosis of the cause and targeted treatment of dysgeusia. Herein, we reviewed published research on the physiological process of taste perception, the potential mechanisms of taste disorders related to SARS-CoV-2 infection, and strategies for prevention and treatment, providing theoretical support for establishing and improving the comprehensive management of COVID-19 complicated by taste disorders.

[Research Progress in the Relationship Between Lactobacillus and Dental Caries]

Lactobacillus is the first microorganism found to be closely associated with dental caries. It demonstrates acidogenicity, aciduricity, and the ability to bind with collagen and to synthesize extracellular polysaccharides to promote bacterial adhesion. Some lactobacilli inhibit the growth of cariogenic bacteria by producing antibacterial compounds or metabolites, competing with cariogenic bacteria for adhesion sites or co-aggregation, or regulating the expression of genes related to cariogenic virulence. Therefore, researchers have, in recent years, experimented with applying Lactobacillusas probiotics in the prevention and control of caries. However, the cariogenic mechanism of Lactobacillus is still not fully understood, and the potential effects, presumably beneficial, of specific Lactobacillus on oral and intestinal microecology remain unknown. More research needs to be done to combine both the cariogenic and probiotic properties of Lactobacillus, and to comprehensively evaluate the effects of Lactobacillus on oral and systemic health. We, herein, summarized research progress in the cariogenicity and caries prevention effect of Lactobacillus, focusing on a discussion of the role of Lactobacillus in cariogenesis, the development of dental caries, and clinical prevention and control of dental caries, in order to provide new ideas and references for the prevention and control of dental caries.

[Latest Research Findings on the Mechanism of Periodontal Pathogens in Cardiovascular Disease]

Cardiovascular disease (CVD) is a major cause of death worldwide. Research findings indicate that periodontal infection is an independent risk factor for CVD. Periodontal pathogens can cause cardiovascular diseases through various pathways, including direct invasion, induction of platelet activation and agglutination, immune inflammatory response, bacteremia, and oxidative stress. Moreover, CVD symptoms are relieved after the patients undergo periodontal interventional treatment. There have been substantial findings indicating that there may be a close connection between periodontal disease and CVD. However, periodontal disease is a chronic disease. The treatment of periodontal diseases and the improvement of periodontal health require long-term efforts. Long-term effective reduction of the incidence of CVD in clinical practice through prevention of periodontal disease remains a challenging area of study. Here we summarized and reported the latest findings on the mechanism of action of periodontal pathogens in cardiovascular diseases, intending to contribute to the better understanding of the pathogenesis of CVD and to provide potential targets and new ideas for its prevention and treatment.

[Development and Influencing Factors of Oral Microbiota in Early Life]

Oral cavity, an important component of and the gateway to the digestive system, is also the colonization site and the microecological environment of trillions of microorganisms. The establishment and succession of oral microbiota are of great importance for the development of human immune system, and function as a major determinant of oral and systemic health. Within a few hours after birth, early colonizers such as Streptococcus and Lactobacillus can be detected in an infant's mouth. The oral microbiota communities mature gradually along with the growth of the host, expanding in their species abundance and diversity. In addition to genetic factors, a number of cross-sectional studies have revealed that the development of oral microecosystems in early life is influenced and tuned by multiple external factors, including maternal health status, mode of delivery, feeding habits, antibiotics use, etc. The dysbiosis of oral microecology in early life is closely related to the pathogenesis and progression of oral and systemic diseases. Therefore, good oral hygiene habits are of vital importance to the early management of oral microbial diseases and their effective prevention and control. Herein, we summarized the colonization and succession of oral microbiota in early life and further discussed the key external factors that affect early life oral microecosystem, as well as the impact of early life oral microbiota on the host's health at a later stage, intending to help providing new insights into and new strategies for the management of the whole lifecycle oral and systemic health.

[Research Updates: Relationship between Gingival Epithelial Intercellular Junctions and Periodontal Pathogenic Bacteria]

Gingival epithelial barrier is the first line of defense of periodontal tissues against the invasion of pathogenic bacteria. The destruction of gingival epithelial barrier is closely related to the development of periodontal disease. Studies have shown that periodontal pathogenic bacteria and their inflammatory microenvironment can inhibit the expression of gingival epithelial junctional proteins via molecular mechanisms such as the downregulation of the expression of grainyhead-like protein family and the upregulation of the methylation level of gene promoter of epithelial connexin, and thus cause damage to the gingival epithelial barrier and the development of periodontitis. We herein reviewed the effects of bacteria and inflammatory factors induced by bacterial infection on gingival epithelial intercellular junctions and related mechanisms, and summarized the research progress on the relationship between gingival epithelial intercellular junctions and periodontal pathogenic bacteria in recent years. Most recent studies were focused on i n vitro cytological experiments and animal models of infections caused by a single kind of bacterium. We have suggested that building gingival epithelial organoid model and combining multi-omics approaches with high resolution three-dimensional electron microscopy are expected to help pinpoint the key microorganisms and their most important virulence factors that trigger periodontal microecologcal imbalance and cause functional damage to the gingival epithelial barrier, to reveal the key molecular mechanisms involved in the maintenance and destruction of gingival epithelial barrier function, and to provide new perspectives on the pathogenesis and the clinical prevention and treatment of periodontitis.