Cigarette smoke has long been known to have a multitude of damaging effects, but thanks to recent research we now know it also fuels the virulent rampage of superbugs. According to a study published in the journal Infection and Immunity by researchers at the University of California, San Diego School of Medicine, antibiotic-resistant bacteria, specifically MRSA, are vastly more difficult to kill when exposed to cigarette smoke.
Methicillin-resistant Staphylococcus aureus, or MRSA, is a type of bacteria that causes life-threatening infections to the skin, bloodstream, or a surgical site, and sometimes causes pneumonia. Originating as a strain of staph infection, MRSA becomes resistant to antibiotics and often affects individuals in hospitals or other health care settings. A disastrous diagnosis due to its innate difficulty to treat, it has become even more threatening with the addition of smoking.
"We already know that smoking cigarettes harms human respiratory and immune cells, and now we've shown that, on the flipside, smoke can also stress out invasive bacteria and make them more aggressive," said Dr. Laura E. Crotty Alexander of UC San Diego and the Veterans Affairs San Diego Healthcare System, in a press release. Crotty Alexander, a pulmonologist, sought to find potential ties between the increased occurrences of MRSA cases in smokers. In order to do so, Crotty Alexander and her team tested two groups of MRSA, one exposed to cigarette smoke extract and one not, to see how each group responded to the defenses of our immune system.
Macrophages, or immune cells known to devour infectious ages, were infected with both types of MRSA (smoke exposed and not) to test the immune response. Although both were able to take up the populations of MRSA, macrophages fighting MRSA exposed to cigarette smoke extract had a significantly harder time killing them.
Researchers found that this type of MRSA was more resistant to the reactive oxygen species, a chemical burst macrophages utilize once they have engulfed bacteria. MRSA exposed to smoke extract was also more resistant to antimicrobial peptides, another line of immune defense used to make holes in bacteria and cause inflammation. Even more alarming was researchers’ discovery that MRSA was able to adhere better to human cells when treated with smoke, assisting in the success of their invasion. This effect depended strongly on dose; the more smoke extract the MRSA was exposed to, the more resistant it became.
Ultimately, the data suggest that through altering the cell walls of the bacteria, cigarette smoke allows MRSA to repel common forms of immune responses. Another study conducted by researchers at University of California, San Diego School of Medicine a year earlier suggested something similar with e-cigarette smoke; vaporized smoke can also alter the structure of MRSA’s cell wall to make it more resistant to bacteria. However, this research also discovered that surface changes to the bacteria increased 10 times more with exposure to cigarette smoke rather than e-cigarette vapor.
"Cigarette smokers are known to be more susceptible to infectious diseases. Now we have evidence that cigarette smoke-induced resistance in MRSA may be an additional contributing factor," Crotty Alexander said. Through their finding, Crotty Alexander and her team hope to add yet another reason to why individuals should refrain from smoking.
Source: Crotty Alexander L, Matthew D, Hwang J, et al. Analysis of the Effects of Cigarette Smoke on Staphylococcal Virulence Phenotypes. Infection and Immunity. 2015.