E-cigarette vapor extract-exposed bacteria were also more virulent in a mouse model of pneumonia.
E-cigaratte vapour is not benign and inhaling high doses daily can kill lung cells, causing inflammatory diseases.
"This study shows that e-cigarette vapour is not benign - at high doses it can directly kill lung cells, which is frightening," said senior author Laura E Crotty Alexander, from the Veterans Affairs San Diego Healthcare System.
"We already knew that inhaling heated chemicals, including the e-liquid ingredients nicotine and propylene glycol, couldn't possibly be good for you," said Crotty Alexander, who is also an assistant clinical professor at University of California, San Diego School of Medicine in US.
"This work confirms that inhalation of e-cigarette vapor daily leads to changes in the inflammatory milieu inside the airways," she said.
The researchers conducted their study in mice. Inflammatory markers - signs of full-body inflammation - in the airways and blood of mice that inhaled e-cigarette vapors for one hour a day, five days a week, for four weeks were elevated by 10 per cent compared to unexposed mice.
"We don't know specifically which lung and systemic diseases will be caused by the inflammatory changes induced by e-cigarette vapor inhalation, but based on clinical reports of acute toxicities and what we have found in the lab, we believe that they will cause disease in the end," Crotty Alexander said.
"Some of the changes we have found in mice are also found in the airways and blood of conventional cigarette smokers, while others are found in humans with cancer or inflammatory lung diseases," she said.
Conversely, bacterial pathogens exposed to e-cigarette vapor benefited.
Specifically, Staphylococcus aureus bacteria were better able to form biofilms, adhere to and invade airway cells and resist human antimicrobial peptides after exposure to e-cigarette vapor.
E-cigarette vapor extract-exposed bacteria were also more virulent in a mouse model of pneumonia. All mice infected with normal methicillin-resistant S aureus (MRSA), an antibiotic-resistant "superbug," survived.
Meanwhile, 25 per cent of mice infected with MRSA pre-exposed to e-cigarette vapor died.
The results were consistent with e-liquids from seven different manufacturers, demonstrating that the findings are not limited to one formula or brand.
The team recently also reported that MRSA bacteria exposed to conventional cigarette smoke are more resistant to killing by the immune system than unexposed bacteria.
The study was published in the the Journal of Molecular Medicine.