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. We have not yet pinpointed the components of e-cigarette vapour that trigger these effects, but preliminary findings suggest that the nicotine in e-juice (the liquid used in e-cigarettes that is vapourised and inhaled) is a significant contributor.
Regular cigarette smoke has more than 5,000 components and nicotine is a small part of this. E-cigarette vapour has many fewer components, so it could mean that nicotine plays a bigger role in the effect we see on MRSA. E-cigarette users take in two to 20 times the amount of vapour in volume, and thus nicotine, than normal smoke. This is because it is so easy to keep inhaling from an e-cigarette – it can keep going for the equivalent of a whole pack of cigarettes, doesn’t make your clothing or breath smell, and can be vaped indoors. This means that vapers are dramatically increasing their intake of nicotine, and therefore increasing the exposure of their colonising bacteria to this substance.
Like cigarette smoke, e-cigarette vapour exposure also weakens our host defences, making it easier for bacteria to cause invasive infections. This means that the vapour is influencing bacteria to be more aggressive and harder to kill, and suppressing the ability of our own cells to attack and kill bacteria.
MRSA in particular is spreadable to other people via touch. There have been outbreaks on school sports teams for example. It is an aggressive bug, so it can cause disease in healthy people as well as the infirm. It already has antibiotic resistance, so making it even more resistant to antimicrobials and killing by host cells is a dangerous thing. It can be incredibly hard to clear MRSA infections, and we are running out of antibiotics powerful enough to eliminate it.
It is hard to believe that anything could be as bad as cigarette smoke. But we simply don’t know enough about the effects of vapour to be able to say that it is a lesser evil. But as best as we can tell from the data we have, e-cigarette vapour is not benign. In fact, it appears that e-cigarette vapour both makes bacteria tougher to kill and weakens the immune system. Together these early findings suggest that people who vape are at increased risk of developing serious bacterial infections.