The Effects of Air Pollution on Respiratory Bacteria

Particulate Matter (PM), a major component of air pollution, is associated with a variety of cardiorespiratory diseases including acute lower respiratory tract infections. It is well established that PM has detrimental effects on the host, causing tissue damage, oxidative stress, and modulating the immune system. However there has been extremely limited research into the effects of PM on bacteria, the organisms responsible for the respiratory infections associated with PM exposure. This project investigated whether Black Carbon (BC), a major component of PM produced as a by-product of fossil fuel combustion, directly affects respiratory tract bacteria. Two model opportunistic pathogens of the respiratory tract were chosen for this investigation, Streptococcus pneumoniae and Staphylococcus aureus. BC was found to alter biofilm formation, structure, matrix composition, and functioning, of both S. pneumoniae and S. aureus, as well as inhibiting planktonic growth. Interestingly, these effects were strain-dependent. Furthermore, BC promoted dissemination of S. pneumoniae from the nasopharynx to the lower respiratory tract in an in vivo murine colonisation model. BC was not observed to alter the respiratory tract microbiota in this project, however a variety of limitations which may have prevented a definitive conclusion being reached are presented. This study provides the first evidence to show that bacteria are directly affected by PM, and thereby suggests that the adverse health effects of PM may not only be due to effects on host tissues, but that modulation of bacterial behaviour may also have a role. The findings of this study therefore show the potential importance of this overlooked field.