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Characterization of nontypable Haemophilus influenzae isolates recovered from adult patients with underlying chronic lung disease reveals genotypic and phenotypic traits associated with persistent infection.

ABSTRACT: Nontypable Haemophilus influenzae (NTHi) has emerged as an important opportunistic pathogen causing infection in adults suffering obstructive lung diseases. Existing evidence associates chronic infection by NTHi to the progression of the chronic respiratory disease, but specific features of NTHi associated with persistence have not been comprehensively addressed. To provide clues about adaptive strategies adopted by NTHi during persistent infection, we compared sequential persistent isolates with newly acquired isolates in sputa from six patients with chronic obstructive lung disease. Pulse field gel electrophoresis (PFGE) identified three patients with consecutive persistent strains and three with new strains. Phenotypic characterisation included infection of respiratory epithelial cells, bacterial self-aggregation, biofilm formation and resistance to antimicrobial peptides (AMP). Persistent isolates differed from new strains in showing low epithelial adhesion and inability to form biofilms when grown under continuous-flow culture conditions in microfermenters. Self-aggregation clustered the strains by patient, not by persistence. Increasing resistance to AMPs was observed for each series of persistent isolates; this was not associated with lipooligosaccharide decoration with phosphorylcholine or with lipid A acylation. Variation was further analyzed for the series of three persistent isolates recovered from patient 1. These isolates displayed comparable growth rate, natural transformation frequency and murine pulmonary infection. Genome sequencing of these three isolates revealed sequential acquisition of single-nucleotide variants in the AMP permease sapC, the heme acquisition systems hgpB, hgpC, hup and hxuC, the 3-deoxy-D-manno-octulosonic acid kinase kdkA, the long-chain fatty acid transporter ompP1, and the phosphoribosylamine glycine ligase purD. Collectively, we frame a range of pathogenic traits and a repertoire of genetic variants in the context of persistent infection by NTHi.

SUBMITTER: Garmendia J

PROVIDER: S-EPMC4019658 | biostudies-literature | 2014

REPOSITORIES: biostudies-literature

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Characterization of nontypable Haemophilus influenzae isolates recovered from adult patients with underlying chronic lung disease reveals genotypic and phenotypic traits associated with persistent infection.

Garmendia Junkal J Viadas Cristina C Calatayud Laura L Mell Joshua Chang JC Martí-Lliteras Pau P Euba Begoña B Llobet Enrique E Gil Carmen C Bengoechea José Antonio JA Redfield Rosemary J RJ Liñares Josefina J

PloS one 20140513 5

Nontypable Haemophilus influenzae (NTHi) has emerged as an important opportunistic pathogen causing infection in adults suffering obstructive lung diseases. Existing evidence associates chronic infection by NTHi to the progression of the chronic respiratory disease, but specific features of NTHi associated with persistence have not been comprehensively addressed. To provide clues about adaptive strategies adopted by NTHi during persistent infection, we compared sequential persistent isolates wit ...[more]

PMID: 24824990

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Project description:Genetic variants arising from within-patient evolution shed light on bacterial adaptation during chronic infection. Contingency loci generate high levels of genetic variation in bacterial genomes, enabling adaptation to the stringent selective pressures exerted by the host. A significant gap in our understanding of phase-variable contingency loci is the extent of their contribution to natural infections. The human-adapted pathogen nontypeable Haemophilus influenzae (NTHi) causes persistent infections, which contribute to underlying disease progression. The phase-variable high-molecular-weight (HMW) adhesins located on the NTHi surface mediate adherence to respiratory epithelial cells and, depending on the allelic variant, can also confer high epithelial invasiveness or hyperinvasion. In this study, we characterize the dynamics of HMW-mediated hyperinvasion in living cells and identify a specific HMW binding domain shared by hyperinvasive NTHi isolates of distinct pathological origins. Moreover, we observed that HMW expression decreased over time by using a longitudinal set of persistent NTHi strains collected from chronic obstructive pulmonary disease (COPD) patients, resulting from increased numbers of simple-sequence repeats (SSRs) downstream of the functional P2hmw1A promoter, which is the one primarily driving HMW expression. Notably, the increased SSR numbers at the hmw1 promoter region also control a phenotypic switch toward lower bacterial intracellular invasion and higher biofilm formation, likely conferring adaptive advantages during chronic airway infection by NTHi. Overall, we reveal novel molecular mechanisms of NTHi pathoadaptation based on within-patient lifestyle switching controlled by phase variation. IMPORTANCE Human-adapted bacterial pathogens have evolved specific mechanisms to colonize their host niche. Phase variation is a contingency strategy to allow adaptation to changing conditions, as phase-variable bacterial loci rapidly and reversibly switch their expression. Several NTHi adhesins are phase variable. These adhesins are required for colonization but also immunogenic, in such a way that bacteria with lower adhesin levels are better equipped to survive an immune response, making their contribution to natural infections unclear. We show here that the major NTHi adhesin HMW1A displays allelic variation, which can drive a phase-variable epithelial hyperinvasion phenotype. Over time, hmw1A phase variation lowers adhesin expression, which controls an NTHi lifestyle switch from high epithelial invasiveness to lower invasion and higher biofilm formation. This reversible loss of function aligns with the previously stated notion that epithelial infection is essential for NTHi infection establishment, but once established, persistence favors gene inactivation, in this case facilitating biofilm growth.

Project description:Objectives: Therapies being safe, effective and not vulnerable to develop resistance are highly desirable to counteract bacterial infections. Host-directed therapeutics is an alternative to conventional antibiotics based on perturbing host pathways subverted by pathogens during their life cycle by the use of host-directed drugs to counteract microbial infections. This study sought to identify cellular genes and pathways differentially expressed during airways epithelial infection by nontypable Haemophilus influenzae (NTHi). NTHi is an opportunistic pathogen that is an important cause of exacerbation of chronic obstructive pulmonary disease (COPD). Based on the proposed relationship between NTHi intracellular location and persistence, the antimicrobial potential of a panel of drugs perturbing host pathways used by NTHi to enter epithelial cells was investigated. Methods: We screened for host genes differentially expressed upon infection by the clinical isolate NTHi375 by analyzing A549 cell whole genome expression profiling, and identified a panel of host target candidates which were pharmacologically modulated. Interfering drugs were tested for their bactericidal effect, cytotoxicity, effect on the interplay NTHi-epithelial cell, and effect on NTHi respiratory infection in vivo, by assessing lung bacterial loads in a murine intranasal infection model. Results: The sirtuin-1 activator resveratrol showed a bactericidal effect against NTHi; the PDE4 inhibitor rolipram showed therapeutic efficacy by lowering NTHi375 counts both intracellularly and in the lungs of infected mice. Conclusions: PDE4 inhibition is currently prescribed in COPD; resveratrol is a geroprotector attractive for COPD treatment by preventing lung aging. This work provides evidence for the antimicrobial potential of rolipram and resveratrol against NTHi respiratory infection. Haemophilus influenzae clinical strain NTHi375 induced gene expression in A549 human type II pneumocyte cell line was measured at 2 h post-infection. Non infected cells were used as a control. Four independent experiments were performed for each condition.

Dataset Information

Characterization of nontypable Haemophilus influenzae isolates recovered from adult patients with underlying chronic lung disease reveals genotypic and phenotypic traits associated with persistent infection.

Publications

Characterization of nontypable Haemophilus influenzae isolates recovered from adult patients with underlying chronic lung disease reveals genotypic and phenotypic traits associated with persistent infection.

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