If you haven't ditched your smoking habit yet, here's another reason why you should: Cigarettes harbor many pathogenic bacteria.

Apparently not only are cigarettes bad news because of the nicotine, but they also contain a wide variety of human bacterial pathogens.

"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."

"If 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."

Bacteria of medical significance to humans were identified in all of the tested cigarettes 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 also suspect that smoking weakens a person's natural immunity, which may be why the respiratory tract of smokers are characterized by higher levels of bacterial pathogens.