Nontypeable Haemophilus influenzae Infection Impedes Pseudomonas aeruginosa Colonization and Persistence in Mouse Respiratory Tract

Abstract

Patients with cystic fibrosis (CF) experience lifelong respiratory infections which are a significant cause of morbidity and mortality. These infections are polymicrobial in nature, and the predominant bacterial species undergo a predictable series of changes as patients age. Young patients have populations dominated by opportunists that are typically found within the microbiome of the human nasopharynx, such as nontypeable Haemophilus influenzae (NTHi); these are eventually supplanted and the population within the CF lung is later dominated by pathogens such as Pseudomonas aeruginosa ( Pa ). In this study, we investigated how initial colonization with NTHi impacts colonization and persistence of Pa in the respiratory tract. Analysis of polymicrobial biofilms in vitro by confocal microscopy revealed that NTHi promoted greater levels of Pa biofilm volume and diffusion. However, sequential respiratory infection of mice with NTHi followed by Pa resulted in significantly lower Pa as compared to infection with Pa alone. Coinfected mice also had reduced airway tissue damage and lower levels of inflammatory cytokines as compared with Pa infected mice. Similar results were observed after instillation of heat-inactivated NTHi bacteria or purified NTHi lipooligosaccharide (LOS) endotoxin prior to Pa introduction. Based on these results, we conclude that NTHi significantly reduces susceptibility to subsequent Pa infection, most likely due to priming of host innate immunity rather than a direct competitive interaction between species. These findings have potential significance with regard to therapeutic management of early life infections in patients with CF.

Acute polymicrobial airway infections: analysis in cystic fibrosis mice

“…aeruginosa resulted in cooperative infection with more significant inflammatory consequences following dual infection (Figs 3–5). These experiments are consistent with our published work seen in non-CF BALB/c mice [12, 13].…”

“…Our recent work showed that in experimental mouse respiratory infections, NTHi diminishes colonization and persistence of P. aeruginosa by priming of innate host defenses [12]. Conversely, in separate studies, we also showed that P.…”

“…influenzae impacted subsequent infection with P. aeruginosa , resulting in decreased bacterial burden and airway tissue damage documented by histopathologic examination [12]. To study these CF pathogens in a disease-specific model, we compared infection outcomes of BALB/c Cftr tm1UNC mice to that of WT, age matched littermates.…”

“…aeruginosa infection. Other inflammatory makers, including IL-1α, IL-1β and IL-6, were not different between infection groups [12]. To assess this phenotype in the BALB/c Cftr tm1UNC mouse model, we measured inflammatory markers in the BALF by multiplex assay.…”

“…aeruginosa infection, including bacterial burden, tissue damage and inflammatory response to P. aeruginosa [12]. Polymicrobial infections in the BALB/c Cftr tm1UNC also showed increased bacterial load and increased infectious consequences, indicating significant cooperativity between S.…”