Web edition: January 27, 2010
The tobacco in cigarettes hosts a bacterial bonanza — literally hundreds of different germs, including those responsible for many human illnesses, a new study finds.
“Nearly every paper that you pick up discussing the health effects of cigarettes starts out with something to the effect that smokers and people exposed to secondhand smoke experience high rates of respiratory infections,” notes Amy Sapkota of the University of Maryland, College Park. The presumption has been that smoking renders people vulnerable to disease by impairing lung function or immunity. And it may well do both.
“But nobody talks about cigarettes as a source of those infections,” she says. Her new data now suggest that’s distinctly possible.
If these germs are alive, something she has not yet confirmed, just handling cigarettes or putting an unlit one to the mouth could be enough to cause an infection.
The idea that tobacco might contain viable germs isn’t just idle conjecture. Several research teams have isolated bacteria from tobacco that they could grow out in petri dishes. Those earlier investigations tended to hunt for — and, when found, attempted to grow — only one or two species of interest, Sapkota says.
What’s novel in her study: She and her colleagues probed for genetic material from any and every bacterium in a cigarette’s tobacco. Under sterile conditions, the researchers opened up cigarettes and then performed a series of tests on the leafy bits. For instance, they isolated all of the ribosomal material and then homed in on its long, species-specific stretches known as 16S regions. These genetic segments were then compared to 16S patches characteristic of known bacterial species.
Sapkota’s team had 16S probes for close to 800 different bacteria and found matches to many hundreds in the four brands of cigarettes screened: Marlboro Red, Camel, Kool Filter Kings and Lucky Strike Original Red. These cigarettes are “among the most commonly smoked brands in Westernized countries and represent three major tobacco companies,” Sapkota notes. All were purchased in Lyon, France, where she was completing her postdoctoral studies.
Among the large number of germs whose DNA laced these cigarettes were: Campylobacter, which can cause food poisoning and Guillain-Barre Syndrome; Clostridium, which causes food poisoning and pneumonias; Corynebacterium, also associated with pneumonias and other diseases; E. coli; Klebsiella, Pseudomonas aeruginosa and Stenotrophomonas maltophilia, all of which are associated not only with pneumonia but also with urinary tract infections; and a number of Staphylococcus species that underlie the most common and serious hospital-associated infections.
Sapkota’s team lists many of these — including the most prevalent bacteria in the tobacco they studied — in a paper published early, online in Environmental Health Perspectives.
Some people have criticized the idea of infectious cigarettes, arguing that as tobacco burns, it would kill any germs present. But Sapkota is not so sure that's true. The tobacco farthest from the burning tip might be a balmy temperature, from a bacterial point of view. And here’s “a really wild idea,” she says: What if the smoke particles traveling through the still-unburned part of a cigarette pick up some germs and then ferry them deeply into the lung, where they’re unlikely to be cleared? Wouldn’t that be the prescription for disease?
Of course, there’s also plenty of chances for a smoker to become exposed prior to lighting up. And, of course, the potential for highest oral exposure would come from chewing tobacco — and nasal exposures from snuff.
Sapkota, an environmental health scientist, plans to follow up her preliminary data to see which types of tobacco are most likely to host viable germs, and whether those bacteria are transported into the body, either during smoking or by the insertion of unburned tobacco products (including chewing tobacco) into the mouth.
Several thousand potentially toxic chemicals have been isolated from cigarettes. Sapkota says that it’s not hard to imagine that the number of germs hosted by tobacco products could rival that of the carcinogens and other poisons residing in or produced by burning tobacco.
How so, when she's only found genetic material indicting hundreds of germs? Owing to the bacterial probes available when Sapkota began her tobacco work, she was only able to screen for 700-odd species. But newer probes on the market can now screen for the bacterial 16S genetic material of 5,000 or more germs. And if she used such huge batteries of probes now, she said she fully expects she could turn up at least 1,000 hitchhiking bacterial species in tobacco products.
Sapkota, A.R., S. Berger, and T.M. Vogel. 2010. Human Pathogens Abundant in the Bacterial Metagenome of Cigarettes. Environmental Health Perspectives (in press). DOI: 10.1289/ehp.0901201
Rubinstein, I. and G.W. Pedersen. 2002. Bacillus Species Are Present in Chewing Tobacco Sold in the United States and Evoke Plasma Exudation from the Oral Mucosa. Clinical and Diagnostic Laboratory Immunology 9(September):1057.
Pauly, J.L., J.D. Waight and G.M. Paszkiewicz. 2008. Tobacco Flakes on Cigarette Filters Grow Bacteria: A Potential Health Risk to the Smoker? Tobacco Control 17(September):i49. doi:10.1136/tc.2007.022772
Rooney, A.P., et al. 2005. Bacterial Species Diversity in Cigarettes Linked to an Investigation of Severe Pneumonitis in U.S. Military Personnel Deployed in Operation Iraqi Freedom. Current Microbiology(July):46. doi:10.1007/s00284-005-4491-z