The debate weighing up the relative harms and benefits of e-cigarettes continues. New evidence suggests that e-cigarettes boost the virulence of drug-resistant pathogens, according to researchers at the VA San Diego Healthcare System and the University of California, San Diego.

A prominent feature in the marketing of e-cigarettes by their manufacturer remains the notion that e-cigarettes are a healthy alternative to traditional cigarettes. However, more and more research is suggesting that e-cigarettes may come with their own attached harms.

In April, the Food and Drug Administration announced proposals to include the currently unregulated e-cigarettes under their regulations for tobacco products. The proposed regulation followed studies assessing the thirdhand smoke risk of e-cigarettes and reports of lung damage linked to e-cigarettes.

Some studies have also questioned whether e-cigarettes actually encourage conventional cigarette smoking, rather than acting as a cessation aid.

Lead author Dr. Laura E. Crotty Alexander told Medical News Today:

"There is mounting evidence that e-cigarettes do not help people quit smoking, or are not any better than other nicotine replacement options. Since we know very little about the short-term and long-term health consequences of vaping e-cigarettes, I still recommend to patients that they use nicotine replacement therapies that are well studied (gum, patches, inhalers)."

Dr. Crotty Alexander and her team grew methicillin-resistant Staphylococcus aureus (MRSA) in culture. They found that exposing the MRSA to e-cigarette vapor - similar in concentration to e-cigarette products available on the market - increased the virulence of the bacteria, making it better able to establish infection in the body and cause more severe disease.

How did the e-cigarette vapor make the MRSA more virulent?

The researchers looked at five factors that contribute to MRSA virulence:

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The researchers found that as well as increasing bacterial virulence, e-cigarette vapor also decreases the ability of human epithelial cells to kill pathogens.
  • Growth rate
  • Susceptibility to reactive oxygen species
  • Surface charge
  • Hydrophobicity
  • Biofilm formation.

The e-cigarette vapor caused alterations in the surface charge and biofilm formation of the MRSA, which provided greater resistance to attack from human cells and antibiotics.

The surface of the bacteria became more positively charged to avoid binding by the animicrobial peptides that are lethal to the pathogen. The bacterial biofilms also became thicker, making the MRSA less vulnerable to attack.

Another possible factor in the increased resistance of the MRSA was a change in pH, which jumped from 7.4 up to 8.4 when exposed to the e-cigarette vapor. This change in pH makes the environment very alkalotic, which stresses the MRSA cells and prompts activation of defense mechanisms.

Overall, the researchers found that as well as increasing bacterial virulence, e-cigarette vapor also decreases the ability of human epithelial cells to kill pathogens.

Effect of boosting MRSA resistance was stronger with cigarette smoke

Although the e-cigarette vapor increased the resistance of this pathogen, which is potentially lethal to humans, the virulence of MRSA was even greater when exposed to conventional cigarette smoke.

The surface charge alterations in the bacteria were 10 times greater when exposed to conventional cigarette smoke, compared with e-cigarette vapor.

Putting this to the test in a mouse model, cigarette smoke-exposed MRSA killed 30% more mice with pneumonia than a control strain of MRSA. The cigarette smoke-exposed MRSA also had four-times greater survival in the lungs than the control MRSA.

E-cigarette-exposed MRSA was also virulent in mice, with a three-times greater survival than the control MRSA.

"Informing my patients of our early research findings may frighten them into avoiding both traditional cigarettes and e-cigarettes," Dr. Crotty Alexander told us, "since both types of cigarettes make drug-resistant bacteria more virulent. But, since in our preliminary studies the effects of the e-cigarettes on bacteria were less than regular cigarettes, patients might still think of them as the lesser of two evils."

Reminding that e-cigarette vapor is not benign, Dr. Crotty Alexander concluded:

"New data from our lab demonstrate that e-cigarette vapor not only increases bacterial virulence but also decreases the ability of human immune cells to fight infection. Thus, my advice to patients remains: it is hard to imagine anything that is worse for you than smoking cigarettes, but we simply don't know enough about e-cigarettes to make recommendations about them. They may cause disease as well."