Cigarette Smoke Increases MRSA's Drug Resistance

Cigarette smoke may help antibiotic-resistant superbugs like Methicillin-resistant Staphylococcus aureus (MRSA) increase their resistance and fight off the immune system, according to a new study in the journal Infection and Immunity.

“Cigarette smoke exposure increases the ability of bacteria (MRSA) to cause invasive disease and death,” says senior author Laura E. Crotty Alexander, MD, assistant clinical professor of medicine at UC San Diego and staff physician at the Veterans Affairs San Diego Healthcare System. “This increase in virulence persists for days after one single cigarette smoke exposure.”
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In fact, the team saw effects when the cigarette smoke was diluted up to fourfold.

“It is hard to know how much cigarette smoke needs to be inhaled to cause these effects on MRSA colonizing the nasopharynx and airways,” Crotty Alexander says. “However, since we showed that the changes persist for days, it is likely that intermittent exposures will lead to persistent changes whether you are the primary smoker or exposed to secondhand smoke.”

Crotty Alexander and her team infected macrophages, immune cells that engulf pathogens, with two types of MRSA—one that had been grown normally and the other that had been grown with cigarette smoke extract.

MRSA treated with cigarette smoke extract was more persistent and deadly. It was better at adhering to and invading human cells that had been grown in the lab and, in a mouse model, it also had a better chance of survival and caused pneumonia with a higher mortality rate. This type of MRSA was also much harder for the macrophages to kill.

“The drug-resistant bacteria sense the more than 4,000 chemicals in the cigarette smoke, many of which are deadly, and arm themselves against these toxins,” Crotty Alexander says. “They protect themselves with armor, making it harder for the cigarette smoke to kill them but also making it harder for the human immune system to kill them.”

When these bacteria face antibiotic pressure, they make similar changes in their surface charge in order to repel antibiotics so they can’t bind with the bacteria and kill them.

“Knowing how the bacteria have changed in response to smoke will help direct antimicrobial therapies,” Crotty Alexander says. “Using antimicrobials that are unaffected by changes in surface charge and hydrophobicity could help circumvent these changes.”

She and her team have many plans for continued research. “These findings have been very intriguing and have led to studies of e-cigarette vapor effects on human innate immune cells and MRSA virulence,” she says.

—Colleen Mullarkey

Reference

McEachern EK, Hwang JH, Sladewski KM, Nicatia S, Dewitz C, Mathew DP, et al. Analysis of the effects of cigarette smoke on staphylococcal virulence phenotypes. Infect Immun. 2015 Mar 30. [Epub ahead of print]