Tobacco smoke makes germs more resilient

UofL dental researcher explores microbiological mechanisms as World Health Organization urges for a day of abstinence from tobacco use

University of Louisville- logoThe mouth is one of the dirtiest parts of the body, home to millions of germs. But puffing cigarettes can increase the likelihood that certain bacteria like Porphyromonas gingivalis will not only set up camp but will build a fortified city in the mouth and fight against the immune system.

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 published today on the BioMedCentral website.

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.

Cigarette smoking alters the mouth microbiota

Smoking significantly changes the mouth's microbiome, with potential implications for tooth decay and the ability to break down toxins, according to results published in the ISME (International Society for Microbial Ecology) Journal.

[girl smoking]
Smokers' mouths have lower levels of the bacteria that break down smoking-related toxins.

Cigarette smoking is the number one cause of preventable disease and mortality in the US, leading to 480,000 deaths annually, or 20% of all deaths.

Over 16 million people live with a smoking-related illness in the US, according to figures from the Centers for Disease Control and Prevention (CDC).

In 2014, the CDC estimated that 16.8% of Americans aged 18 years and over were cigarette smokers, or around 40 million adults.

Much recent research has focused on imbalances in the gut microbiota and how they relate to immune disorders such as Crohn's disease and gastrointestinal cancers.

There are around 600 species of bacteria in the human mouth. Over 75% of oral cancers are thought to be linked to smoking, but it remains unclear whether microbial differences in the mouth affect the risk for cancer.

Higher levels of Streptococcus in smokers' mouths

Researchers from New York University Langone Medical Center and its Laura and Isaac Perlmutter Cancer Center have been using precise genetic tests to investigate the impact of smoking on the composition and action of oral microbiota.

Fast facts about quitting smoking

  • In the US, there are more former smokers than current smokers, according to the CDC
  • In 2010, 68.8% of American smokers wanted to quit
  • In 2013, 48% of smokers in high school had tried to quit in the past year.

Learn more about quitting smoking

The team used mouthwash samples from 1,204 American adults who are registered in a large, ongoing study into cancer risk, funded by the National Institutes of Health (NIH) and the American Cancer Society (ACS).

Participants were all aged 50 years or over. Among them were 112 smokers and 521 individuals with no history of smoking. There were also 571 people who had quit smoking, 17% of them having stopped within the past 10 years.

Using genetic tests and statistical data, the researchers analyzed the thousands of bacteria residing in the mouths of volunteers.

Results suggest that the oral microbiome of smokers is significantly different from that of people who have never smoked or are no longer smoking. In the mouths of smokers, the levels of 150 bacterial species were significantly higher, while levels of 70 other species were distinctly lower.

Proteobacteria made up 4.6% of overall bacteria in the mouths of smokers, compared with 11.7% in nonsmokers. Proteobacteria are thought to play a part in breaking down the toxic chemicals introduced by smoking.

By contrast, 10% more species of Streptococcus were found in the mouths of smokers, compared with nonsmokers. Streptococcus is known to promote tooth decay.

Recovery comes after quitting smoking

On quitting smoking, however, the oral microbiome appears to return to its previous state. In people who had smoked previously, but not in the last 10 years, the microbial balance was the same as in the mouths of nonsmokers.

Senior investigator and epidemiologist Jiyoung Ahn, PhD, says:

"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."

Co-lead investigator Brandilyn Peters, PhD, points out that the results do not reveal how long it takes former smokers' microbiome to find its balance after quitting.

The authors are planning further studies to establish the precise timeline for recovery of the bacterial community in the mouth.

They also hope to understand the biological changes that occur in the oral microbiome as a result of smoking, and how these changes might affect the risk for various cancers of the mouth and elsewhere in the body.

Medical News Today recently reported on research suggesting that the effect of some smoking cessation therapies may be limited.

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