Superbugs Are More Aggressive With Cigarette Smoke

Researchers at the University of California, San Diego have discovered that Methicillin-resistant Staphylococcus aureus (MRSA) bacteria exposed to cigarette smoke became even more resistant to killing by the immune system.

"We already know that smoking cigarettes harms human respiratory and immune cells, and now we've shown that, on the flipside, smoke can also stress out invasive bacteria and make them more aggressive," Laura E. Crotty Alexander, senior author of the study, said in a news release.

For the study, researchers tested the bacteria's susceptibility to individual mechanisms' macrophages employ to kill bacteria. When they were inside the macrophages, smoke-exposed MRSA was more resistant to the killing of reactive oxygen species, the chemical burst that macrophages use to destroy their microbial meals.

Furthermore, they found that smoke-exposed MRSA was more resistant to killing by antimicrobial peptides that poke holes in bacterial cells and trigger inflammation. And the more smoke extract used, the more resistant the MRSA became.

Mouse models exposed to cigarette smoke had a higher mortality rate and experienced higher rates of pneumonia, overall. MRSA treated with cigarette smoke extract was better at sticking to cells and invading in the tissues during growth.

Researchers found that due to the alteration of the cell walls, cigarette smoke strengthens MRSA bacteria in such a way that it's better able to repel antimicrobial peptides and other particles.

"Cigarette smokers are known to be more susceptible to infectious diseases. Now we have evidence that cigarette smoke-induced resistance in MRSA may be an additional contributing factor," Crotty Alexander said.