According to new research conducted by scientists from the University of Maryland and the Ecole Centrale de Lyon in France, smokers may face another serious health risk from the habit and the tobacco industry may have another serious PR problem on their hands as a result.

A study appearing in the upcoming issue of Environmental Health Perspectives suggests that Cigarettes are "widely contaminated" with bacteria, including some known to cause disease in people. The research team describes the study as the first to show that "cigarettes themselves could be the direct source of exposure to a wide array of potentially pathogenic microbes among smokers and other people exposed to secondhand smoke."

"The commercially-available cigarettes that we tested were chock full of bacteria, as we had hypothesized, but we didn't think we'd find so many that are infectious in humans, explains Amy R. Sapkota, an assistant professor in the University of Maryland's School of Public Health.

Bacteria of medical significance to humans were identified in all of the tested cigarettes (Camel; Kool Filter Kings; Lucky Strike Original Red; and Marlboro Red) and included Acinetobacter (associated with lung and blood infections); Bacillus (some varieties associated with food borne illnesses and anthrax); Burkholderia (some forms responsible for respiratory infections); Clostridium (associated with foodborne illnesses and lung infections); Klebsiella (associated with a variety of lung, blood and other infections); and Pseudomonas aeruginosa (an organism that causes 10 percent of all hospital-acquired infections in the United States).

The researchers describe the study as the first snapshot of the total population of bacteria in cigarettes. Previous researchers have taken small samples of cigarette tobacco and placed them in cultures to see whether bacteria would grow. But Sapkota's team took a more holistic approach using DNA microarray analysis to estimate the so-called bacterial metagenome, the totality of bacterial genetic material present in the tested cigarettes.

They warn that "[i]f these organisms can survive the smoking process—and we believe they can—then they could possibly go on to contribute to both infectious and chronic illnesses in both smokers and individuals who are exposed to environmental tobacco smoke."  

While the public health implications of the study are potentially very serious, the authors urge caution going forward and explain that more research is needed to reach a conclusive answer.

"Now that we've shown that a pack of cigarettes is loaded with bacteria, we will conduct follow-up research to determine the possible roles of these organisms in tobacco-related diseases." Sapkota says.

For example, do cigarette-borne bacteria survive the burning process and go on to colonize smokers' respiratory systems? Existing research suggests that some hardy bacteria can be transmitted this way, the researchers say.

This might account for the fact that the respiratory tracts of smokers are characterized by higher levels of bacterial pathogens. But it's also possible that smoking weakens natural immunity and the bacteria come from the general environment rather than from cigarettes. Further research will be needed to determine the possible health impacts of cigarette-borne bacteria.

Citation: Amy R. Sapkota, Sibel Berger, and Timothy M. Vogel, 'Human Pathogens Abundant in the Bacterial Metagenome of Cigarettes', Environmental Health Perspectives, 2009, doi: 10.1289/ehp.0901201