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. Ultimately, the data suggest that through altering the cell walls of the bacteria, cigarette smoke allows MRSA to repel common forms of immune responses. 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. 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. 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. 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. / NIAID 
 
 The study stated it was performed to examine an alternative to the prevailing theory that cigarette smoke mostly causes disease by harming the smoker. "Because MRSA causes severe pneumonia more often than MSSA, and because MRSA commonly colonizes the nasopharynx and airways and thus is exposed to inhaled substances, we examined the effect of cigarette smoke on MRSA resistance to host innate immune killing mechanisms and the ability to cause pneumonia in mice," the study stated. Study co-authors include Elisa K. McEachern, John H. Hwang, Katherine M. Sladewski, UC San Diego and Veterans Affairs San Diego Healthcare System; Shari Nicatia, UC San Diego, Veterans Affairs San Diego Healthcare System and Utrecht University; Carola Dewitz, UC San Diego, Veterans Affairs San Diego Healthcare System and University of Veterinary Medicine, Hannover, Germany; Denzil P. Mathew, Veterans Affairs San Diego Healthcare System; and Victor Nizet, UC San Diego.
– Superbugs such as MRSA are already bad enough. But it turns out that something can make them even nastier: cigarette smoke. Researchers found that antibiotic-resistant bacteria exposed to the smoke became more aggressive and far more difficult to kill, they explain at Eureka Alert. It's almost as if the smoke sets off an alarm that causes the bacteria to strengthen its defenses, explains the Union-Tribune of San Diego. Scientists made the discovery by exposing immune cells to two different batches of MRSA, one normal and one treated with cigarette smoke extract. The bigger the dose of smoke, the bigger the effect, notes Medical Daily. "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," says lead author Laura Crotty Alexander of UC San Diego. It's a double-whammy: Smokers already have weakened immune systems that make them more susceptible to infectious diseases, and the smoke they inhale seems to make invading pathogens even more dangerous. In this study, the smoke helped MRSA survive longer and kill more mice with pneumonia. (The latest antibiotic-resistant bug to make headlines is a nasty stomach virus.)