Exposure to cigarette smoke can further drug resistance in methicillin-resistant Staphylococcus aureus (MRSA) strains, researchers find.
Tobacco smoking represents the leading preventable cause of death worldwide. Smoking is a known risk factor for several health conditions, including lung cancer, cardiovascular disease, and chronic obstructive pulmonary disorder. Smoking also increases susceptibility to infectious disease.
Previous research has found that smoking reduces the immune system’s ability to respond to infection. A team from the University of Bath has reported that cigarette smoke can change the DNA and characteristics of pathogenic bacteria to enable a more persistent infection.
The researchers focused on Staphylococcus aureus, a microbe that is normally present in the nasopharynx of 30-60% of the population. S. aureus causes many infections that range in severity from uncomplicated skin infections to pneumonia and endocarditis. While antibiotics remain the first line of treatment, the emergence and spread of antibiotic-resistant strains of bacteria, such as methicillin-resistant S. aureus (MRSA), is a global health concern.
The new study appears in Scientific Reports. The authors conducted lab-based experiments using six strains of MRSA chosen for their clinical relevance and genetic diversity. The researchers aimed to determine the impact of cigarette smoke on bacterial virulence, which refers to the ability of a microorganism to cause disease.
Bacteria were grown in the presence of cigarette smoke and added to cultured human lung cells to assess toxicity and invasiveness. Smoke-exposed S. aureus was associated with properties that benefited disease progression, including increased biofilm formation, reduced toxicity, and greater intracellular persistence. However, the effect of cigarette smoke varied among strains and not all strains responded the same way.
Critically, exposure to cigarette smoke induced the formation of small colony variants (SCVs) for some strains. SCVs are slow-growing, hardy bacterial subpopulations that have been linked to the recurrence of chronic infections in smokers. The researchers found that cigarette smoke triggers an intracellular stress response, resulting in an accelerated mutation rate and SCV formation. Of note, S. aureus SCVs were better able to resist the antibiotic, rifampicin, which suggests that resistance to other antibiotics may also be affected following smoke exposure.
“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,” said Dr. Maisem Laabei, University of Bath Department of Biology & Biochemistry researcher and lead author of the study.
Laabei and her team hope that the link between cigarette smoke and heightened bacterial virulence will highlight the importance of smoking cessation.
Written by Cheryl Xia, HBMSc
References:
- Melvin, C. Cigarette smoke makes MRSA superbug bacterium more drug-resistant. EurekAlert! (2019).
- Lacoma, A. et al. Cigarette smoke exposure redirects Staphylococcus aureus to a virulence profile associated with persistent infection. Sci Rep 9, 10798 (2019).
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