Pseudomonas aeruginosaCan Inhibit Growth of Streptococcal Species via Siderophore Production

Abstract

AbstractCystic Fibrosis (CF) is a genetic disease that causes patients to accumulate thick, dehydrated mucus in the lung and develop chronic, polymicrobial infections due to reduced mucociliary clearance. These chronic polymicrobial infections and subsequent decline in lung function are significant factors in the morbidity and mortality of CF.Pseudomonas aeruginosaandStreptococcusspp. are among the most prevalent organisms in the CF lung; the presence ofP. aeruginosacorrelates with lung function decline and theStreptococcus millerigroup (SMG), a subgroup of the viridans streptococci, is associated with exacerbations in patients with CF. Here we characterize the interspecies interactions that occur between these two genera. We demonstrated that multipleP. aeruginosalaboratory strains and clinical CF isolates promote the growth of multiple SMG strains and oral streptococci in anin vitrococulture system. We investigated the mechanism by whichP. aeruginosaenhances growth of streptococci by screening for mutants ofP. aeruginosaPA14 unable to enhanceStreptococcusgrowth, and we identified theP. aeruginosa pqsL::TnMmutant, which failed to promote growth ofS. constellatusandS. sanguinis. Characterization of theP. aeruginosaΔpqsLmutant revealed that this strain cannot promoteStreptococcusgrowth. Our genetic data and growth studies support a model whereby theP. aeruginosaΔpqsLmutant overproduces siderophores, and thus likely outcompetesStreptococcus sanguinisfor limited iron. We propose a model whereby competition for iron represents one important means of interaction betweenP. aeruginosaandStreptococcusspp.ImportanceCystic fibrosis (CF) lung infections are increasingly recognized for their polymicrobial nature. These polymicrobial infections may alter the biology of the organisms involved in CF-related infections, leading to changes in growth, virulence and/or antibiotic tolerance, and could thereby affect patient health and response to treatment. In this study, we demonstrate interactions betweenP. aeruginosaand streptococci using a coculture model, and show that one interaction between these microbes is likely competition for iron. Thus, these data indicate that one CF pathogen may influence the growth of another and add to our limited knowledge of polymicrobial interactions in the CF airway.