Smoking Zaps Healthy Bacteria In the Mouth

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Smoking causes the body to turn against its own helpful bacteria, leaving smokers more vulnerable to disease.

Despite the daily disturbance of brushing and flossing, the mouth of a healthy person contains a stable ecosystem of healthy bacteria.

New research shows that the mouth of a smoker is a much more chaotic, diverse ecosystem -- and is much more susceptible to invasion by harmful bacteria.

As a group, smokers suffer from higher rates of oral diseases -- especially gum disease -- than do nonsmokers, which is a challenge for dentists, according to Purnima Kumar, assistant professor of periodontology at Ohio State University. She and her colleagues are involved in a multi-study investigation of the role the body's microbial communities play in preventing oral disease.

"The smoker's mouth kicks out the good bacteria, and the pathogens are called in," said Kumar. "So they're allowed to proliferate much more quickly than they would in a non-smoking environment."

"A few hours after you're born, bacteria start forming communities called biofilms in your mouth," said Kumar. "Your body learns to live with them, because for most people, healthy biofilms keep the bad bacteria away."

She likens a healthy biofilm to a lush, green lawn of grass. "When you change the dynamics of what goes into the lawn, like too much water or too little fertilizer," she said, "you get some of the grass dying, and weeds moving in." For smokers, the "weeds" are problem bacteria known to cause disease.

"When you compare a smoker and nonsmoker, there's a distinct difference," said Kumar. "The first thing you notice is that the basic 'lawn,' which would normally contain thriving populations made of a just few types of helpful bacteria, is absent in smokers."

The team found that for nonsmokers, bacterial communities regain a similar balance of species to the communities that were scraped away during cleaning. Disease-associated bacteria are largely absent, and low levels of cytokines show that the body is not treating the helpful biofilms as a threat.

"By contrast," said Kumar, "smokers start getting colonized by pathogens -- bacteria that we know are harmful -- within 24 hours. It takes longer for smokers to form a stable microbial community, and when they do, it's a pathogen-rich community."

Smokers also have higher levels of cytokines, indicating that the body is mounting defenses against infection. Clinically, this immune response takes the form of red, swollen gums -- called gingivitis -- that can lead to the irreversible bone loss of periodontitis.

In smokers, however, the body is not just trying to fight off harmful bacteria. The types of cytokines in smokers' gum swabs showed the researchers that smokers' bodies were treating even healthy bacteria as threatening.

Although they do not yet understand the mechanisms behind these results, Kumar and her team suspect that smoking is confusing the normal communication that goes on between healthy bacterial communities and their human hosts.

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The above story is reprinted, with editorial adaptation by the Zestzfulness Team, from materials in the Feb. 15, 2012 news release by Ohio State University.

The results of the study were published in the journal Infection and Immunity: P. S. Kumar, C. R. Matthews, V. Joshi, M. de Jager, M. Aspiras. Tobacco Smoking Affects Bacterial Acquisition and Colonization in Oral Biofilms. Infect Immun, 2011; 79 (11): 4730 DOI: 10.1128/IAI.05371-11