Smoking weakens the immune system and lowers the ability of human cells to fight infection – research has shown this over and over again. Smoking cigarettes, and breathing in second-hand smoke, puts people at risk for developing severe lung and respiratory track infections. Smokers are two to four times more likely to develop pneumococcal pneumonia than non-smokers. Cigarette smoking also increases the rates and severity of influenza infection and increases the risk of tuberculosis.

But what if the problem isn’t just that cigarette smoke weakens the immune system, but actually makes the bacteria more aggressive?

Antibiotic resistant bacteria are a growing problem worldwide. MRSA (Methicillin Resistant Staphylococcus aureus) is one of the most common, causing thousands of deaths every year. About 20% of people are colonised by MRSA, and the nasal passages are the most common site for these bacteria to live. Because this organism inhabits an area that is exposed to inhaled substances and is a common cause of invasive disease, we began studying it in the lab. I hypothesised that cigarette smoke would put stress on bacterial cells, just as it does on human cells, and that the bacteria would respond by protecting and arming themselves.

Our research, recently presented at the American Thoracic Society’s international conference in San Diego, has found that cigarette smoke increases the resistance of MRSA to being killed by a host’s immune cells. In particular, cigarette smoke induced resistance to antimicrobial peptides – substances produced by human cells, which kill bacteria like antibiotics do.

As the e-cigarette market boomed, I wondered if e-cigarette vapour would have the same effects, so we ran parallel studies on the effects of it on MRSA virulence. We have found over the past few months that both regular cigarette smoke and e-cigarette vapour make drug-resistant bacteria more virulent.  Read more: e-cigarettes makes MRSA bacteria more aggressive.