Understanding the Pathogenicity of Burkholderia contaminans, an Emerging Pathogen in Cystic Fibrosis

Abstract

Several bacterial species from the Burkholderia cepacia complex (Bcc) are feared opportunistic pathogens that lead to debilitating lung infections with a high risk of developing fatal septicemia in cystic fibrosis (CF) patients. However, the pathogenic potential of other Bcc species is yet unknown. To elucidate clinical relevance of Burkholderia contaminans, a species frequently isolated from CF respiratory samples in Ibero-American countries, we aimed to identify its key virulence factors possibly linked with an unfavorable clinical outcome. We performed a genome-wide comparative analysis of two isolates of B. contaminans ST872 from sputum and blood culture of a female CF patient in Argentina. RNA-seq data showed significant changes in expression for quorum sensing-regulated virulence factors and motility and chemotaxis. Furthermore, we detected expression changes in a recently described low-oxygen-activated (lxa) locus which encodes stress-related proteins, and for two clusters responsible for the biosynthesis of antifungal and hemolytic compounds pyrrolnitrin and occidiofungin. Based on phenotypic assays that confirmed changes in motility and in proteolytic, hemolytic and antifungal activities, we were able to distinguish two phenotypes of B. contaminans that coexisted in the host and entered her bloodstream. Whole genome sequencing revealed that the sputum and bloodstream isolates (each representing a distinct phenotype) differed by over 1,400 mutations as a result of a mismatch repair-deficient hypermutable state of the sputum isolate. The inferred lack of purifying selection against nonsynonymous mutations and the high rate of pseudogenization in the derived isolate indicated limited evolutionary pressure during evolution in the nutrient-rich, stable CF sputum environment. The present study is the first to examine the genomic and transcriptomic differences between longitudinal isolates of B. contaminans. Detected activity of a number of putative virulence factors implies a genuine pathogenic nature of this novel Bcc species.

Genomic and phenotypic characterization of Burkholderia isolates from the potable water system of the International Space Station

“…Using antiSMASH [43] we verified that each of the ISS isolates and the reference strain contain the occidiofungin and pyrrolnitrin gene cluster (gene clusters presented in S6 Table). The antifungal metabolite, occidiofungin, as well as pyrrolnitrin are known to also display hemolytic properties [44], which can break down heme in the hemoglobin of host bodies causing complications for the host. Due to the identification of B. contaminans isolates harboring these two biosynthetic gene clusters within our collection, we assayed for the ability to inhibit growth of the Aspergillus fumigatus AF293 strain ( Fig 8A) and to cause hemolysis ( Fig 8B).…”

Genomic and phenotypic characterization ofBurkholderiaisolates from the potable water system of the International Space Station

“…Using antiSMASH [28] we verified that each of the ISS isolates and the reference strain contain the occidiofungin and pyrrolnitrin gene cluster. The antifungal metabolite, occidiofungin, as well as pyrrolnitrin are known to also display hemolytic properties [29], which can break down heme in the hemoglobin of host bodies causing complications for the host.…”

Class III Histidine Kinases: a Recently Accessorized Kinase Domain in Putative Modulators of Type IV Pilus-Based Motility

“…The list of genomes that contain HKIII genes is enriched with plant, animal, and human pathogens, providing additional support for a hypothesis that these signal transduction systems control TFP-mediated motility, a well-known virulence factor (41)(42)(43)(44)(45)(46). Many of the species that contain HKIIIs are associated with infections in cystic fibrosis and immunocompromised patients, including Burkholderia cepacia (47), B. cenocepacia (48), B. contaminans (49), B. gladioli (50), B. multivorans (50,51), B. vietnamiensis (50), Pandoraea apista (50), P. pulmonicola (50), P. sputorum (52), and Ralstonia pickettii (50), among others. Other HKIII-bearing human pathogens include Kingella kingae, which is linked to septic arthritis, osteomyelitis, spondylodiscitis, meningitis, endocarditis, and lower respiratory tract infections (53), as well as Burkholderia ferrarie and B. fungorum, which are implicated in synovial tissue infection and vaginosis (54,55).…”