Microbial changes associated with advancing periodontitis in STR/N mice

A 16S rRNA Gene and Draft Genome Database for the Murine Oral Bacterial Community

Mouse model studies are frequently used in oral microbiome research, particularly to investigate diseases such as periodontitis and caries, as well as other related systemic diseases. We have reported here the details of the development of a curated reference database to characterize the oral microbial community in laboratory and some wild mice.

A curated murine oral microbiome database to be used as a reference for mouse-based studies has been constructed using a combination of bacterial culture, 16S rRNA gene amplicon, and whole-genome sequencing. The database comprises a collection of nearly full-length 16S rRNA gene sequences from cultured isolates and draft genomes from representative taxa collected from a range of sources, including specific-pathogen-free laboratory mice, wild Mus musculusdomesticus mice, and formerly wild wood mouse Apodemus sylvaticus. At present, it comprises 103 mouse oral taxa (MOT) spanning four phyla—Firmicutes, Proteobacteria, Actinobacteria, and Bacteroidetes—including 12 novel undescribed species-level taxa. The key observations from this study are (i) the low diversity and predominantly culturable nature of the laboratory mouse oral microbiome and (ii) the identification of three major murine-specific oral bacterial lineages, namely, Streptococcus danieliae (MOT10), Lactobacillus murinus (MOT93), and Gemella species 2 (MOT43), which is one of the novel, still-unnamed taxa. Of these, S. danieliae is of particular interest, since it is a major component of the oral microbiome from all strains of healthy and periodontally diseased laboratory mice, as well as being present in wild mice. It is expected that this well-characterized database should be a useful resource for in vitro experimentation and mouse model studies in the field of oral microbiology.

IMPORTANCE Mouse model studies are frequently used in oral microbiome research, particularly to investigate diseases such as periodontitis and caries, as well as other related systemic diseases. We have reported here the details of the development of a curated reference database to characterize the oral microbial community in laboratory and some wild mice. The genomic information and findings reported here can help improve the outcomes and accuracy of host-microbe experimental studies that use murine models to understand health and disease. Work is also under way to make the reference data sets publicly available on a web server to enable easy access and downloading for researchers across the world.

Genetic susceptibility to chronic periodontal disease

Evidence suggests that there is a significant genetic component to susceptibility and resistance to chronic periodontal disease. Data from both clinical studies and studies using animal models are reviewed here. Also outlined are the genomic methods that are now available for identifying susceptibility and resistance loci.

Disorder of salivary secretion in inbred polydipsic mouse

To find mechanisms of an extreme polydipsia in an inbred strain of mice, STR/N, this study was undertaken using Institute of Cancer Research (ICR) mice as a control. During food deprivation, daily water intake of both strains decreased. The decrement in the STR/N mice was larger than that in the ICR mice. During dehydration, daily food intake of the STR/N mice was smaller than that of the ICR mice. These data indicate that prandial drinking was more severely affected for the STR/N mice. Under anesthesia, the stimulated salivary secretion by pilocarpine of the STR/N mice was significantly smaller than that of the ICR mice. The submandibular gland of the STR/N mice was lighter and harder than that of the ICR mice. After desalivation from the major three salivary glands, the ICR mice drank as much as the STR/N mice. Young STR/N mice with undeveloped polydipsia did not show different salivary secretion stimulated by pilocarpine from the young ICR mice. These findings indicate a dysfunction with age in the salivary glands of the STR/N mice, and they suggest that the decreased saliva induces thirst and triggers extraordinary drinking in the polydipsic mice.

Oral microbial ecology and the role of salivary immunoglobulin A

In the oral cavity, indigenous bacteria are often associated with two major oral diseases, caries and periodontal diseases. These diseases seem to appear following an imbalance in the oral resident microbiota, leading to the emergence of potentially pathogenic bacteria. To define the process involved in caries and periodontal diseases, it is necessary to understand the ecology of the oral cavity and to identify the factors responsible for the transition of the oral microbiota from a commensal to a pathogenic relationship with the host. The regulatory forces influencing the oral ecosystem can be divided into three major categories: host related, microbe related, and external factors. Among host factors, secretory immunoglobulin A (SIgA) constitutes the main specific immune defense mechanism in saliva and may play an important role in the homeostasis of the oral microbiota. Naturally occurring SIgA antibodies that are reactive against a variety of indigenous bacteria are detectable in saliva. These antibodies may control the oral microbiota by reducing the adherence of bacteria to the oral mucosa and teeth. It is thought that protection against bacterial etiologic agents of caries and periodontal diseases could be conferred by the induction of SIgA antibodies via the stimulation of the mucosal immune system. However, elucidation of the role of the SIgA immune system in controlling the oral indigenous microbiota is a prerequisite for the development of effective vaccines against these diseases. The role of SIgA antibodies in the acquisition and the regulation of the indigenous microbiota is still controversial. Our review discusses the importance of SIgA among the multiple factors that control the oral microbiota. It describes the oral ecosystems, the principal factors that may control the oral microbiota, a basic knowledge of the secretory immune system, the biological functions of SIgA, and, finally, experiments related to the role of SIgA in oral microbial ecology.