Cigarette Smoke Boosts Virulence Potential of S aureus, Making It More Resistant

Cigarette smoke may affect the virulence of certain bacterial strains of Staphylococcus aureus, making the pathogen more resistant to antibiotics, according to a new study from investigators at the University of Bath in the United Kingdom.

The research team sought to evaluate the effects of cigarette smoke on the bacteria that inhabit the nasopharynx and/or upper respiratory tract—areas directly exposed to cigarette smoke—given its known association with immune dysregulation and increased risk of infectious disease.

Investigators exposed 6 genetically distinct, clinically relevant methicillin-resistant S aureus (MRSA) isolates to cigarette smoke to analyze how this contact altered specific virulence phenotypes known to be important in animal models of infection.

The findings, published in Scientific Reports, were quite surprising, according to Maisem Laabei, PhD, a lecturer in microbiology in the Department of Biology and Biochemistry at the University of Bath, and co-author on the study.

“Our results indicated that cigarette smoke increased biofilm formation, invasion, and persistence within alveolar epithelial cells and reduced toxin production. Surprisingly, cigarette smoke exposure also significantly accelerated small colony variant (SCV) formation,” he said. “SCVs are resistant to a number of antibiotics and are associated with chronic infections as they are highly invasive and can persist within human cells making them very difficult to treat. Taken together, our results suggest that MRSA exposed to cigarette smoke redirects its virulence potential to one associated with persistent, difficult-to-treat infections.”

Also, interestingly, the team “observed that S aureus community-acquired (CA-) MRSA strains (JKD6159, MW2 and JE2 [USA300]) are better able to survive and replicate within cigarette smoke-[tryptic soy broth] than health care-acquired (HA) MRSA (EMRSA-15; CA/HA MRSA strain, TW20 and MRSA252) and lab strains (SH1000 and Newman).”

Upon further investigation into the observation that cigarette smoke accelerated SCV formation, the research team found that cigarette smoke exposure also enhanced the frequency of mutations in S aureus, according to Laabei.

“We then showed that a specific DNA repair pathway was involved, and that cigarette smoke resulted in DNA damage, triggering this pathway which resulted in more mutations and accelerated SCV formation,” he said. “Our results indicate that cigarette smoke exposure can significantly alter many aspects of S aureus physiology and virulence. We now need to investigate how this occurs with low grade exposure over longer time periods, in essence trying to mimic a more in vivo environment.”