Strains of methicillin resistant Staphylococcus aureus - MRSA - can become more resistant to antibiotics when exposed to cigarette smoke, researchers have found. Some strains of S. aureus microbes are harmless while others like MRSA are far more dangerous. S. aureus bacteria are found in anywhere from thirty to sixty percent of people worldwide. It wasn’t true of every strain tested, but cigarette smoke caused some of the infectious strains to become more invasive and persistent. The findings have been published in Scientific Reports.
"Smoking is the leading cause of preventable death worldwide, and cigarette smoke has over 4,800 compounds within it. We wanted to study S. aureus because it's so common in humans and it can cause a range of diseases, so we wanted to see what happened when we exposed it to smoke,” explained the lead study author Dr. Maisem Laabei of the University of Bath's Department of Biology & Biochemistry.
In this work, the international research team selected six clinically relevant reference strains of MRSA known to cause a variety of disorders including pneumonia and skin infections. The genetically diverse group of microbial strains were then exposed to cigarette smoke. They didn’t all have the same reaction, but some became more resistant to the antibacterial effect of rifampicin, and were more persistent and invasive.
Cigarette smoke is thought to be an environmental stressor that triggers an emergency response in S. aureus cells; the mutation rate in the DNA of the microbes increases, raising the likelihood that a persister that can resist antibiotics will be created.
The research also connected this stress to the growth of tough populations of cells called Small Colony Variants (SCVs), which previous work has linked with chronic infections in smokers. Other studies have also suggested that the increased incidence of infection in smokers was attributable to immune system impairment caused by cigarette smoke. This study indicates that the smoke is also impacting microbes in a way that raises the chance of dangerous infection.
"These Small Colony Variants are highly adhesive, invasive and persistent. They can sit around for a long time, are difficult to kick out, and are linked to chronic infections. We hope that our work provides another reason for people not to smoke and for current smokers to quit," added Laabei.
"We expected some effects but we didn't anticipate smoke would affect drug-resistance to this degree. We recognize that exposure in a lab is different to inhaled smoke over a long time, but it seems reasonable to hypothesize, based on our research and others' that stressful conditions imposed by smoking induce responses in microbial cells leading to adaptation to harsh conditions, with the net effect of increasing virulence and/or potential for infection," added Laabei.
Next, the investigators want to see whether air pollution is having a similar effect on bacteria living in our nasal passages.
Sources: AAAS/Eurekalert! via University of Bath, Scientific Reports