New evidence from scientists at the University of Bath suggests that the ability of the superbug, methicillin-resistant Staphylococcus aureus (MRSA), to resist antibiotics is enhanced by the presence of cigarette smoke.¹

Cigarette smoking is one of the most important modifiable risk factors for many health problems including cancer, cardiovascular and metabolic disorders, as well as many pulmonary diseases.² Containing an estimate of 5,000 chemicals, cigarette smoke is probably the most significant source of toxic chemical exposure to the human body.³ One of the key components in cigarette smoke, reactive oxygen species (ROS), are responsible for the altered composition of respiratory tract microbiota due to their bactericidal effects. Researchers believe that the stress exerted by these chemicals can trigger an emergency ‘SOS’ response; this response increases the rate of DNA mutation resulting in highly resistant strains such as MRSA. ¹

S. aureus, a common pathogenic component of the commensal flora of the human respiratory tract, is associated with various types of infection ranging from skin infection to endocarditis.⁴ Its highly adaptive ability – especially that of MRSA strains – facilitates its emergence as an important respiratory pathogen.

The study, which focused on six strains of MRSA clones (selected based on their clinical significance and genetic diversity), demonstrated that cigarette smoking leads to MRSA strains developing  a greater resistance to rifampicin – as well as an increase in invasiveness and persistence.¹ The possibility of developing resistance to other antibiotics was also speculated, although the responses in this study varied between the strains. The study also reported that the increased virulence was closely related to the emergence of Small Colony Variants (SCVs) – a sub-population of S. aureus which is less susceptible to antibiotics.¹ The increased frequency of these colonies was linked to a mutation caused by exposure to cigarette smoke. SCVs have been known to be responsible for chronic infections due to their ability to survive harsh environments.⁵

The lead author, Dr Maisem Laabei, said that his team chose S. aureus because it is a typical disease-contracting bacterium in humans.⁶ Reflecting on the results, he stated that his team did not anticipate that the impact of cigarette smoking on drug resistance would reach the extent that it did. He also explained that SCVs are highly adhesive, invasive, persistent and very difficult to treat.⁶

Dr Laabei and his colleagues recognised that the impact of laboratory exposure to cigarette smoke is quite different to that associated with long-term cigarette smoking.⁶ However, they believe that the stressful conditions imposed by cigarette smoking will result in adaptive responses and promote virulence and/or potential for infection.

The increased virulence of MRSA due to exposure to cigarette smoking is an alarming revelation to the already known challenging health problems caused by these superbugs. With a huge number of smokers globally, it may be making a considerable contribution to the escalating antimicrobial-resistance problem. Furthermore, the researchers anticipate that other kind of aerosol pollutants might have similar impact on bacterial virulence.

References

1. Lacoma A, et al. Sci Rep 2019;9:10798
2. Onor IO, et al. Int J Environ Res Public Health 2017;14:1147
3. Talhout R, et al. Int J Environ Res Public Health 2011;8:613–628
4. Parker D, Prince A. Semin Immunopathol 2012;34:281–297
5. Proctor RA, et al. Nat Rev Microbiol 2006;4:295–305
6. Melvin C. University of Bath: Cigarette smoke makes MRSA superbug bacterium more drug-resistant. Available at: https://www.bath.ac.uk/announcements/cigarette-smoke-makes-mrsa-superbug-bacterium-more-drug-resistant/. Accessed 5 September 2019.