Identifying the killer in cystic fibrosis

Lack of cable pili expression by cblA-containing Burkholderia cepacia complex

The Burkholderia cepacia complex consists of several closely related bacterial species (or genomovars) which although generally not pathogenic for healthy individuals, contribute significantly to morbidity and mortality among persons with cystic fibrosis (CF). Certain B. cepacia complex strains are more frequently recovered from CF sputum cultures than are others, and these typically reside in genomovar III. The ET12 clone is a genomovar III strain that predominates among CF patients in Canada and the United Kingdom and is characterized by distinctive cblA-encoded pili that have a cable-like morphology. In a previous survey of B. cepacia complex isolates recovered from 606 CF patients in the US, a single genomovar III ET12 isolate (isolate AU0007) was identified; several cblA-containing genomovar I isolates, however, were also detected. In the study reported here, analysis by PFGE revealed several distinct strain types among these genomovar I isolates, and sequence analysis of their cblA genes demonstrated 87.8-88.4% identity to the ET12 cblA sequence. Southern analysis indicated that the cblA variant from each genomovar I isolate resides on a 4 kbp EcoRI fragment, in contrast to ET12 isolates, in which cblA localizes to a 5 kbp EcoRI fragment. Western blot assay indicated expression of the 16 kDa major pilin subunit by ET12 isolates, including AU0007, but neither whole-cell nor surface-protein extracts of the genomovar I reacted. Electron microscopy revealed the complete absence of pili expression by the genomovar I isolates. In contrast to typical ET12 isolates, AU0007 appeared to be hyperpiliated with rigid pili that lacked the cable morphology and did not bind cytokeratin 13, which has been previously identified as the epithelial cell receptor for the ET12 cable-pili-associated adhesin.

The structure of a polysaccharide from infectious strains of Burkholderia cepacia

The structure of an acidic exopolysaccharide (EPS) from eight strains of Burkholderia cepacia has been investigated by methylation and sugar analysis, periodate oxidation-Smith degradation, and partial acid-hydrolysis. An enzyme preparation obtained from the same organisms producing the EPS was also used to depolymerize the polysaccharide. Detailed NMR studies of the chemical and enzymatic degradation products showed that this EPS consists of a highly branched heptasaccharide-repeating unit with the following structure: [abstract: see text]. About three O-acetyl groups per repeating unit are present at undetermined positions.

Structure of succinoglycan from an infectious strain of Agrobacterium radiobacter

The exopolysaccharide produced by a cystic fibrosis clinical isolate of Agrobacterium radiobacter was shown by monosaccharide and methylation analyses, degradation with succinoglycanase and NMR analysis to be a succinoglycan with the structure shown below. (S)-pyruvic acid is found stoichiometrically as 4,6-O-ketal substituent of terminal glucose. Succinic acid is present in 40% of the repeating units and it is attached to O-6 of the 3-linked glucose next to the pyruvate carrying sugar. Some evidence is found that a small amount of succinic acid (ca. 6% of the total) is linked to O-6 of another undetermined glucose. [structure: see text]

An epidemic of burkholderia cepacia transmitted between patients with and without cystic fibrosis

Burkholderia cepacia is an important pathogen in cystic fibrosis (CF) and an infrequent cause of nosocomial infection in non-CF patients. This report describes a large hospital outbreak that appeared to involve both patient groups, a previously unrecognized phenomenon. Ribotype restriction fragment length polymorphism (RFLP) profiles and pulsed-field gel electrophoresis-resolved macrochromosomal RFLPs were analyzed, a ribotype-based phylogenic tree was constructed, and case-control and cohort studies were performed. A single dominant clone was found in both CF and non-CF groups. Phylogenic analysis suggests that it has evolved independently and that such highly transmissible strains can emerge rapidly and randomly. Acquisition risk in the CF patients was linked to hospitalization (odds ratio=5.47, P=.0158, confidence interval=1. 28-26.86) and was associated with significantly increased mortality rates. Infection control policies must now consider this threat of transmission between non-CF and CF patients.

Burkholderia cepacia. Management issues and new insights

Although Burkholderia cepacia colonizes a relatively small proportion of individuals with cystic fibrosis (CF), it is associated with significant morbidity and mortality, and has had a profound impact on infection control practices. This article reviews the current understanding of the epidemiology of B. cepacia infection, describes important recent developments in the microbiology and taxonomy of this species, and presents issues that remain obstacles to defining the optimal management of B. cepacia infection in CF.

Pulmonary evolution of cystic fibrosis patients colonized by Pseudomonas aeruginosa and/or Burkholderia cepacia

We analysed the pulmonary evolution (radiological scores and pulmonary function) of 81 cystic fibrosis (CF) patients colonized by Pseudomonas aeruginosa (PA), by Burkholderia cepacia (BC) or by both these bacteria, compared to a control group. Pulmonary function was compared in the age bracket 6-13 years. Functional vital capacity (FVC) and forced expiratory volume (FEV1) values for PA colonized patients were significantly worse than for the control group but better than for children colonized by both organisms. In this last group, the evolution of radiological scores and pulmonary function showed a greater decline 2 years after the first colonization compared to the other groups. FVC and FEV1 values in patients colonized by BC were not worse than these of patients colonized by PA. Moreover, BC affected older patients with advanced lung disease and often previously colonized with PA. These results suggested that co-colonization by PA and BC could be a more deleterious factor on the pulmonary evolution than the isolated colonization by PA or BC, and that BC could be a severity marker rather than a cause. In addition, after starting the utilization of mouthpieces with filter at single use for spirometry in 1993 (without any other change in preventive measures already taken during hospitalization), incidence of BC decreased from 8.2% to zero, and no new case of BC colonization has been observed over the last 4 years.

CONCLUSION

Co-colonization of CF patients by PA and BC is more deleterious for pulmonary evolution than colonization by one of these bacteria alone. Re-inforcement of environmental measures during hospitalization (e.g. use of disposable mouthpieces for spirometry) was sufficient to reduce the transmission of BC.

Microbial pathogenesis in cystic fibrosis: mucoid Pseudomonas aeruginosa and Burkholderia cepacia

Respiratory infections with Pseudomonas aeruginosa and Burkholderia cepacia play a major role in the pathogenesis of cystic fibrosis (CF). This review summarizes the latest advances in understanding host-pathogen interactions in CF with an emphasis on the role and control of conversion to mucoidy in P. aeruginosa, a phenomenon epitomizing the adaptation of this opportunistic pathogen to the chronic chourse of infection in CF, and on the innate resistance to antibiotics of B. cepacia, person-to-person spread, and sometimes rapidly fatal disease caused by this organism. While understanding the mechanism of conversion to mucoidy in P. aeruginosa has progressed to the point where this phenomenon has evolved into a model system for studying bacterial stress response in microbial pathogenesis, the more recent challenge with B. cepacia, which has emerged as a potent bona fide CF pathogen, is discussed in the context of clinical issues, taxonomy, transmission, and potential modes of pathogenicity.