Inhaling cigarette smoke drastically alters the composition of the oral microbiome, according to the results of a study published this month in the International Society for Microbial Ecology Journal. While more research is needed in order to establish a concrete connection between this effect and the development of smoking-related diseases, evidence suggests that changes to the bacterial populations in smokers’ mouths could increase their susceptibility to the toxic effects of tobacco smoke.
To conduct this research, scientists from the NYU Langone Medical Center took mouthwash samples from a group of 1,204 individuals, made up of current and past smokers, as well as non-smokers. They analyzed the microbial DNA in these samples in order to determine the prevalence of the various bacteria present in the mouths of participants.
In doing so, they found that the oral microbiome of current smokers differed greatly from that of both past smokers and non-smokers, noting that cigarettes appear to promote the growth of over 150 different bacterial species while inhibiting the proliferation of a further 70. However, the fact no difference was found between the samples of former smokers and those who had never taken up the habit suggests that this effect is not permanent, and can be reversed by giving up smoking.
Alarmingly, many bacterial species belonging to the phylum Proteobacteria were found to be sharply reduced in the mouths of smokers. These microorganisms are known to play a key role in breaking down many of the toxic components of tobacco smoke, such as polycyclic aromatic hydrocarbon and xylene. As such, a loss of these bacteria is likely to have negative consequences for smokers’ health.
Conversely, bacteria of the phylum Streptococcus were discovered to be more populous in the mouths of smokers than non-smokers. These bacteria have previously been associated with an increased risk of periodontal disorders, implying that cigarettes could lead to the development of gum disease.
The cause of this disruption to the oral microbiome has a number of possible explanations. For instance, as cigarette smoke decreases the availability of oxygen in the mouth, it creates an environment that favours anaerobic bacteria over aerobic bacteria. Given that many Streptococcus species are anaerobes while Proteobacteria are generally aerobic, this theory would seem to be plausible.
Alternatively, smoking has been shown to increase the acidity of saliva, generating conditions in which acid-tolerant microbes like Streptococcus are able to thrive. Certain chemicals in cigarette smoke have also been shown to have antibiotic effects, which could explain why some bacteria become depleted when exposed to it.
Taken as a whole, this study appears to provide ample evidence that some of the negative health effects associated with smoking may be partially mediated or enhanced by changes in oral microbiota. However, lead researcher Jiyoung Ahn explained in a statement that “further experiments will be needed… to prove that these changes weaken the body's defenses against cancer-causing chemicals in tobacco smoke, or trigger other diseases in the mouth, lungs, or gut.”