Methicillin-resistant Staphylococcus aureus (MRSA) bacteria that are exposed to cigarette smoke become even more resistant, researchers have found. The study is published in Infection and Immunity.

Researchers from the University of California, San Diego School of Medicine sought to see whether cigarette smoke and MRSA infections influenced each other. Macrophages were infected with MRSA and grown either normally or with cigarette smoke extract. The team found that it was more difficult to kill the MRSA-exposed to cigarette smoke extract than MRSA without the exposure, though the macrophages were able to take up the two bacterial populations equally.

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The MRSA-exposed to smoke were more resistant to killing by reactive oxygen species and by antimicrobial peptides. The MRSA resistance went up with greater smoke extract exposure, which indicated this was a dose-dependent effect. In addition, the MRSA exposed to cigarette smoke were more successful at sticking to and invading human cells grown in the lab. They also survived longer and caused pneumonia with a higher mortality rate when tested in a mouse model.

The study findings indicate that cigarette smoke enables MRSA bacteria to repel antimicrobial peptides and other charged particles, enhancing their resistance. This may place cigarette smokers at increased susceptibility to infectious diseases, authors conclude.

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