How are bacteria involved in the detrimental health outcomes caused by exposure to air pollutants?

With an annual death toll of 7 million, the effect of air pollution on human morbidity and mortality is a major global problem. Air pollution associated with infectious respiratory disease is responsible for a mortality rate of 1.5 million annually. However, the impact of air pollution on bacterial behaviour is largely unknown. Our work has shown for the first time that black carbon (BC), a major component of air pollution, increases dissemination of colonising Streptococcus pneumoniae and Staphylococcus aureusin in-vivo infection models, and also alters biofilm structure, composition, and function. However, the biological mechanisms responsible for dissemination in the host and biofilm alterations by BC are unknown. BC is known to elicit an oxidative stress in eukaryotic tissues, therefore we hypothesise that the S. aureus oxidative stress response may play an important role in the bacterial response to BC. Our data shows that exposure to BC is toxic to S. aureusand that oxidative stress response of mutant strains show increased sensitivity to BC than the wildtype strain. Transcriptional analysis demonstrated that the expression of key oxidative stress genes in the oxidative stress response pathway are induced in the presence of BC. These findings demonstrate that BC has a metabolic effect on S. aureus and that the oxidative stress response is required for bacterial survival to BC. Furthermore, the induction of the S. aureus oxidative stress response may be important for increased dissemination in the host through adaptation of bacterial cells to the host immune response.