The researchers say their analysis is the most comprehensive to date to examine the effects of smoking on the make-up and action of bacterial species in the human mouth based on precise genetic testing.

Recent work in the field links imbalances in microbial populations in the gut to such immune disorders as Crohn’s disease, as well as to some gastrointestinal cancers. Experts estimate that more than three-quarters of oral cancers are tied to smoking, but it remains to be seen whether smoking-related microbial differences in the mouth contribute to disease risk.

“Our study is the first to suggest that smoking has a profound impact on the oral microbiome,” says study senior investigator and epidemiologist Jiyoung Ahn, PhD.

“Further experiments will be needed, however, 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,” says Ahn, an associate professor at NYU Langone and associate director of population sciences at its Laura and Isaac Perlmutter Cancer Center.

Microbiome Bounces Back

The NYU Langone team relied on mouthwash samples from 1,204 American men and women whose health is already being monitored as part of larger ongoing cancer risk studies funded by the National Institutes of Health and the American Cancer Society. Study volunteers were all age 50 or older and included 112 smokers, 571 former smokers (among whom 17 percent had quit within the past 10 years), and 521 people who never smoked. The team then used genetic tests and statistical analyses to tell apart the thousands of bacteria in each study participant’s mouth.

Importantly, the investigators found that the oral microbiome of smokers differed significantly from that of people who had never smoked and those who had quit smoking. The team also found that the oral microbiome of smokers bounces back after they quit smoking, with all former smokers (who had not smoked for at least 10 years) showing the same microbial balance as nonsmokers.

More than 150 bacterial species showed significantly increased growth in the mouths of smokers, while another 70 showed sharp decreases in growth. For instance, smokers had relatively fewer species of Proteobacteria (at 4.6 percent of overall bacteria in the mouth), than nonsmokers (at 11.7 percent), with Proteobacteria shown to be involved in the breakdown of toxic chemicals introduced by smoking. By contrast, smokers had 10 percent more species of Streptococcus than nonsmokers, with Streptococcus known to promote tooth decay.

Postdoctoral fellow and study co-lead investigator Brandilyn Peters, PhD, cautions that study data did not enable researchers to tell how long it actually takes former smokers to rebalance their oral microbiomes after they stop smoking. But, she adds, further experiments are planned to determine the precise timeline for microbiome recovery.

Ahn says their goal is to identify what happens biologically from smoking-related changes in the oral microbiome. The team also plans to investigate how these smoking-related changes might influence risk for various cancers of the mouth and other parts of the body.

University of Louisville School of Dentistry researcher David A. Scott, Ph.D., explores how cigarettes lead to colonization of bacteria in the body. Scott and his research team have identified how tobacco smoke, composed of thousands of chemical components, is an environmental stressor and promotes bacteria colonization and immune invasion.

Scott says since this initial finding several years ago, a recent literature review published in Tobacco Induced Diseases revealed that cigarette smoke and its components also promote biofilm formation by several other pathogens including Staphylococcus aureus, Streptococcus mutans, Klebsiella pneumonia and Pseudomonas aeruginosa.

Biofilms are composed of numerous microbial communities often made up of complex, interacting and co-existing multispecies structures. Bacteria can form biofilms on most surfaces including teeth, heart valves and the respiratory tract.

“Once a pathogen establishes itself within a biofilm, it can be difficult to eradicate as biofilms provide a physical barrier against the host immune response, can be impermeable to antibiotics and act as a reservoir for persistent infection,” Scott said. “Furthermore, biofilms allow for the transfer of genetic material among the bacterial community and this can lead to antibiotic resistance and the propagation of other virulence factors that promote infection.”

One of the most prevalent biofilms is dental plaque, which can lead to gingivitis — a gum disease found in almost half the world’s population — and to more severe oral diseases, such as chronic periodontitis. Bacterial biofilms also can form on heart valves resulting in heart-related infections, and they also can cause a host of other problems.

“We are continuing research to understand the interactions of the elaborate communities within biofilms and how they relate to disease. Many studies have investigated biofilms using single species, but more relevant multispecies models are emerging. Novel treatments for biofilm-induced diseases also are being investigated, but we have a long way to go,” Scott said.

Scott elaborates on this research in a short question and answer style blog to be published May 31 on the BioMedCentral website: http://blogs.biomedcentral.com/on-health/2016/05/31/wntd-author-qa/

Attention to Scott’s work comes as the World Health Organization observes World No Tobacco Day on May 31 to encourage a global 24-hour abstinence from all forms of tobacco consumption. The effort points to the annual 6 million worldwide deaths linked to the negative health effects of tobacco use.

In the United States, Kentucky ranks second for cigarette use among adults, according the Centers for Disease Control and Prevention (CDC). Only West Virginia has more smokers. Kentucky also brings up the rear among youth in grades 9-12 who use tobacco; according to 2011 CDC data, about 24-percent of high school students smoke cigarettes.