Salivary mucins play active role to fight cavities

		IMAGE: The viscoelastic properties of mucus and saliva are attributed to mucins, large glycoproteins that play a key role in host defense and maintaining a healthy microbiome. Human salivary mucins protect... Click here for more information.

Salivary mucins, key components of mucus, actively protect the teeth from the cariogenic bacterium, Streptococcus mutans, according to research published ahead of print in Applied and Environmental Microbiology. The research suggests that bolstering native defenses might be a better way to fight dental caries than relying on exogenous materials, such as sealants and fluoride treatment, says first author Erica Shapiro Frenkel, of Harvard University, Cambridge, MA.

S. mutans attaches to teeth using sticky polymers that it produces, eventually forming a biofilm, a protected surface-associated bacterial community that is encased in secreted materials, says Frenkel. As S. mutans grows in the biofilm, it produces organic acids as metabolic byproducts that dissolve tooth enamel, which is the direct cause of cavities. "We focused on the effect of the salivary mucin, MUC5B on S. mutansattachment and biofilm formation because these are two key steps necessary for cavities to form," says Frenkel.

		IMAGE: This is two overlayed fluorescent microscopy images ofStreptococcus mutans, the primary bacteria responsible for dental cavities. When S. mutans forms biofilms on the tooth surface, it produces organic acids... Click here for more information.

"We found that salivary mucins don't alterS. mutans' growth or lead to bacterial killing over 24 hours," says Frenkel. "Instead, they limit biofilm formation by keeping S. mutans suspended in the liquid medium. This is particularly significant forS. mutans because it only causes cavities when it is attached, or in a biofilm on the tooth's surface." She adds that the oral microbiome is better preserved when naturally occurring species aren't killed. "The ideal situation is to simply attenuate bacterial virulence," she says.

The study grew out of previous work in the investigators' laboratory showing that other types of mucins, such as porcine gastric mucins, had protective effects against common lung pathogens, says Frenkel. With this in mind, they suspected that salivary mucins would play a protective role, but they were not sure what that would be.

		IMAGE: This is a fluorescent microscopy image of a Streptococcus mutans biofilm. Click here for more information.

"Defects in mucin production have been linked to common diseases such as asthma, cystic fibrosis, and ulcerative colitis," says Frenkel. "There is increasing evidence that mucins aren't just part of the mucus for structure or physical protection, but that they play an active role in protecting the host from pathogens and maintaining a healthy microbial environment. We wanted to apply these emerging ideas to a disease model that is a widespread, global public health problem--cavities. We chose to study the interaction of MUC5B with Streptococcus mutans because it is the primary cavity-causing bacteria in the oral cavity."

The research makes a fundamental contribution to scientific understanding of host-microbe interactions, says principal investigator Katharina Ribbeck, of the Massachusetts Institute of Technology, Cambridge MA. "It is generating a paradigm shift from the textbook view of mucus as a simple catchall filter for particles, towards the understanding that mucus is a sophisticated bioactive material with powerful abilities to manipulate microbial behavior."

Sleeping in dentures doubles the risk of pneumonia in the elderly

Poor oral health and hygiene are increasingly recognized as major risk factors for pneumonia among the elderly. To identify modifiable oral health-related risk factors, lead researcher Toshimitsu Iinuma, Nihon University School of Dentistry, Japan, and a team of researchers prospectively investigated associations between a constellation of oral health behaviors and incidences of pneumonia in the community-living of elders 85 years of age or older. This study, titled "Denture Wearing During Sleep Doubles the Risk of Pneumonia in Very Elderly," has been published by the International and American Associations for Dental Research (IADR/AADR in the OnlineFirst portion of the Journal of Dental Research (JDR)

At baseline, 524 randomly selected seniors (228 males, 296 females, average age was 87.8 years old) were examined for oral health status and oral hygiene behaviors as well as medical assessment, including blood chemistry analysis, and followed up annually until first hospitalization for or death from pneumonia. Over a three-year follow-up period, 48 events associated with pneumonia were identified (20 deaths and 28 acute hospitalizations). Among 453 denture wearers, 186 (40.8%) who wore their dentures during sleep, were at higher risk for pneumonia than those who removed their dentures at night.

In a multivariate Cox model, both perceived swallowing difficulties and overnight denture wearing were independently associated with approximately 2.3-fold higher risk of the incidence of pneumonia, which was comparable with the high risk attributable to cognitive impairment, history of stroke and respiratory disease. In addition, those who wore dentures while sleeping were more likely to have tongue and denture plaque, gum inflammation, positive culture for Candida albicans, and higher levels of circulating interleukin-6 as compared to their counterparts.

This study provides empirical evidence that denture wearing during sleep is associated not only with oral inflammatory and microbial burden but also with incident pneumonia, suggesting potential implications of oral hygiene programs for pneumonia prevention in the community. Frauke Mueller, University of Geneva, Switzerland, wrote a perspective titled "Oral Hygiene Reduces the Mortality From Aspiration Pneumonia in Frail Elders," commenting that these findings lead to a simple and straight forward clinical recommendation—denture wearing during the night should be discouraged in geriatric patients.