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 wherein the predominant bacterial species changes as patients age. Young patients have populations dominated by pathobionts such as nontypeable Haemophilus influenzae (NTHi), that are eventually supplanted by pathogens such as Pseudomonas aeruginosa (Pa), which are more typical of late-stage CF disease. 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 infection of mice with NTHi followed by Pa showed significant reduction in Pa in the lungs as compared to infection with Pa alone. Coinfected mice also had reduced severity of airway tissue damage and lower levels of inflammatory cytokines as compared mice infected with Pa alone. Similar results were observed using heat-inactivated NTHi bacteria prior to Pa introduction. Based on these results, we conclude that NTHi can significantly reduce susceptibility to subsequent Pa infection, most likely due to immune priming 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

“…Bacterial challenge with S. maltophilia and P. 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].…”

“…We carried out polymicrobial bacterial infections in BALB/c Cftr tm1UNC and Cftr tm1UncTg (FABPhCFTR)1Jaw/J mice, evaluating early infection response and bacterial clearance. As we have observed previously, NTHi infection caused innate immune priming that can reduce both colonization and pathology associated with subsequent P. 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. maltophilia and P. aeruginosa populations in vivo.…”

“…In previous work, we showed that preceding infection with nontypeable H. 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.…”

“…Our previous work showed that sequential introduction of NTHi followed by P. aeruginosa resulted in significant reduction of some inflammatory markers, including MCP-1, TNF-α and anti-inflammatory marker IL-10 in dual-infected mice compared to a single-species P. 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.…”

“…As patients age, these microbes are gradually supplanted by other bacterial species, most notably mucoid variants of Pseudomonas aeruginosa, which often correlates with declining respiratory function and worsened disease outcomes [10,11]. 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. aeruginosa can promote colonization of other bacteria, namely Stenotrophomonas maltophilia, by means of cooperative persistence within polymicrobial biofilms [13].…”