Cigarette smoke makes MRSA more aggressive, study finds

When methicillin-resistant Staphylococcus aureus bacteria are exposed to cigarette smoke, they become even more resistant to being killed by a person's immune system, according to research out of the University of California, San Diego School of Medicine.

For the study, researchers infected macrophages with MRSA. Some of the MRSA were grown normally, while some were grown with cigarette smoke extract. They found the macrophages infected with smoke-exposed MRSA had a more difficult time killing the bacteria.

Additionally, researchers found MRSA treated with cigarette smoke were better at invading human cells grown in a lab. Also, smoke-exposed MRSA survived better and caused pneumonia with a higher mortality rate in a mouse experiment.

"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," said Crotty Alexander, MD, a pulmonologist and the study's senior author.

Dr. Alexander added, "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."

The study was published in Infection and Immunity.

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