Burkholderia cepacia: medical, taxonomic and ecological issues

A melanin pigment purified from an epidemic strain of Burkholderia cepacia attenuates monocyte respiratory burst activity by scavenging superoxide anion

The acquisition of Burkholderia cepacia in some cystic fibrosis patients is associated with symptoms of acute pulmonary inflammation that may be life threatening. The ability of lipopolysaccharide (LPS) from B. cepacia to prime a monocyte cell line for enhanced superoxide anion generation was investigated and compared with the priming activities of LPSs from Pseudomonas aeruginosa, Stenotrophomonas maltophilia, and Escherichia coli. The human monocyte cell line MonoMac-6 (MM6) was primed overnight with different LPSs (100 ng/ml), and the respiratory burst was triggered by exposure to opsonized zymosan (125 micrograms/ml). Superoxide generation was detected by enhanced chemiluminescence with Lucigenin. B. cepacia LPS was found to prime MM6 cells to produce more superoxide anion than P. aeruginosa or S. maltophilia LPS, and this priming response was CD14 dependent. In addition, the inhibition of respiratory burst responses in monocytes by a bacterial melanin-like pigment purified from an epidemic B. cepacia strain was investigated. The melanin-like pigment was isolated from tyrosine-enriched media on which B. cepacia had been grown and was purified by gel filtration, anion ion-exchange chromatography, and ethanol precipitation. The scavenging potential of the melanin-like pigment for superoxide anion radical (*O2-) generated during the respiratory burst was confirmed with superoxide produced from a cell-free system with xanthine-xanthine oxidase and detected by electron paramagnetic resonance spectroscopy with the spin trap 5-diethoxyphosphoryl-5-methyl-1-pyrroline-n-oxide. The addition of melanin during the LPS priming stage had no effect on the subsequent triggering of the respiratory burst, but melanin inhibited *O2- detection when added at the triggering stage of the respiratory burst. We conclude that melanin-producing B. cepacia may derive protection from the free-radical-scavenging properties of this pigment.

Quorum sensing in Burkholderia cepacia: identification of the LuxRI homologs CepRI

Burkholderia cepacia has emerged as an important pathogen in patients with cystic fibrosis. Many gram-negative pathogens regulate the production of extracellular virulence factors by a cell density-dependent mechanism termed quorum sensing, which involves production of diffusible N-acylated homoserine lactone signal molecules, called autoinducers. Transposon insertion mutants of B. cepacia K56-2 which hyperproduced siderophores on chrome azurol S agar were identified. One mutant, K56-R2, contained an insertion in a luxR homolog that was designated cepR. The flanking DNA region was used to clone the wild-type copy of cepR. Sequence analysis revealed the presence of cepI, a luxI homolog, located 727 bp upstream and divergently transcribed from cepR. A lux box-like sequence was identified upstream of cepI. CepR was 36% identical to Pseudomonas aeruginosa RhlR and 67% identical to SolR of Ralstonia solanacearum. CepI was 38% identical to RhlI and 64% identical to SolI. K56-R2 demonstrated a 67% increase in the production of the siderophore ornibactin, was protease negative on dialyzed brain heart infusion milk agar, and produced 45% less lipase activity in comparison to the parental strain. Complementation of a cepR mutation restored parental levels of ornibactin and protease but not lipase. An N-acylhomoserine lactone was purified from culture fluids and identified as N-octanoylhomoserine lactone. K56-I2, a cepI mutant, was created and shown not to produce N-octanoylhomoserine lactone. K56-I2 hyperproduced ornibactin and did not produce protease. These data suggest both a positive and negative role for cepIR in the regulation of extracellular virulence factor production by B. cepacia.

Lung transplantation for cystic fibrosis

Lung transplantation currently stands as the only therapeutic option that carries the potential to restore patients with advanced cystic fibrosis to a more normal state of health. Nonetheless, the procedure carries significant risk and median survival following transplantation is only 5 years. This article discusses the currently achievable outcomes and the common short-comings of transplantation. Strategies to optimize outcomes through appropriate patient selection, use of living donors, and novel research initiatives are discussed.

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.

Phenotypic variation of lipid composition in Burkholderia cepacia: a response to increased growth temperature is a greater content of 2-hydroxy acids in phosphatidylethanolamine and ornithine amide lipid

Burkholderia cepacia produces an unusual range of polar lipids, which includes two forms each of phosphatidylethanolamine (PE) and ornithine amide lipid (OL), differing in the presence or absence of 2-hydroxy fatty acids. By using chemostat cultures in chemically defined media, variations in the lipid content and the proportions of individual lipids have been studied as a function of (a) growth temperature, (b) growth rate and (c) growth-limiting nutrient (carbon, magnesium, phosphorus or oxygen). Total cellular lipid in carbon-limited cultures was lowest at high growth temperatures and low growth rates. Increases in growth temperature over the range 25-40 degrees C led to increases in the proportions of molecular species of PE and OL containing 2-hydroxy acids, without changing the PE:OL ratio. Growth temperature did not alter the balance between neutral and acidic lipids, but the contribution of phosphatidylglycerol to the latter increased with rising growth temperature and growth rate. Pigmentation of cells and the presence of flagella were also temperature-dependent. Change in growth rate also affected the PE:OL ratio and the extent to which monoenoic acids were replaced by their cyclopropane derivatives. Whereas similar lipid profiles were found for carbon-, magnesium- and oxygen-limited cultures, ornithine amides were the only polar lipids detected in phosphorus-limited cells.

Distribution of mevalonate and glyceraldehyde 3-phosphate/pyruvate routes for isoprenoid biosynthesis in some gram-negative bacteria and mycobacteria

Labeling experiments using [1-13C]acetate or [1-13C]glucose were performed with opportunistic pathogenic bacteria, with innocuous bacteria related to pathogenic species or with phytopathogenic species. The labeling pattern was determined in the isoprenic moiety of ubiquinone or menaquinone derivatives. These experiments showed that Acinetobacter, Citrobacter, Erwinia, Pseudomonas, Burkholderia, Ralstonia and Mycobacterium synthesize their isoprenoids via the mevalonate-independent glyceraldehyde 3-phosphate/pyruvate route. Enzymes of this novel bacterial metabolic route, which is apparently absent in vertebrates and man, therefore represent potential targets for a novel type of antibacterial drugs.

Comparison of culture and PCR for detection of Burkholderia cepacia in sputum samples of patients with cystic fibrosis

We investigated the utility of PCR to detect Burkholderia cepacia directly in sputum samples at two cystic fibrosis (CF) centers serving children and adults. Following liquefaction of the sputa by using N-acetyl-L-cysteine, DNA was isolated and analyzed by PCRs with three different primer pairs directed toward bacterial rRNA loci. Two primer pairs were putatively specific for B. cepacia. The other pair, which universally amplifies a band from all bacteria, served as a control. Sputum samples were obtained from 219 patients and analyzed independently by culture and by PCR to detect B. cepacia. The analyses were performed blinded with respect to each other. The results of the PCR with sputa demonstrated that the primers directed to the 16S loci demonstrated approximately 95% concordance with culture results and were more specific than those amplifying the 16S to 23S spacer region. In addition, the 16S primer pair putatively identified B. cepacia in seven patients whose sputa were culture negative at this time. Of these culture-negative patients, five had sputum samples that were culture positive for B. cepacia either prior or subsequent to this study. The results of this study indicate the utility of PCR as a diagnostic method for the rapid identification of B. cepacia in sputum samples of CF patients. We anticipate that improvements in our taxonomic understanding may allow the design of more specific primers for detection of each species of the B. cepacia complex in sputum samples.

The detection of insertion sequences within the human pathogen Burkholderia pseudomallei which have been identified previously in Burkholderia cepacia

Using primers designed from the nucleotide sequences of five insertion elements identified previously in Burkholderia cepacia, the presence of two insertion sequences (IS406 and IS407) was detected in chromosomal DNA isolated from strains of the human pathogen Burkholderia pseudomallei. The IS407 homologue was cloned from B. pseudomallei NCTC 4845 and nucleotide sequenced to confirm its identity and degree of homology with B. cepacia IS407. A PCR amplification product from B. pseudomallei NCTC 4845 DNA provided an IS407 probe which was used to determine, by Southern blotting, the number and location of copies of IS407 in ten strains of B. pseudomallei and four representatives from three of the five genomovars of B. cepacia.

Burkholderia cepacia produces a hemolysin that is capable of inducing apoptosis and degranulation of mammalian phagocytes

Burkholderia cepacia is an opportunistic pathogen that has become a major threat to individuals with cystic fibrosis (CF). In approximately 20% of patients, pulmonary colonization with B. cepacia leads to cepacia syndrome, a fatal fulminating pneumonia sometimes associated with septicemia. It has been reported that culture filtrates of clinically derived strains of B. cepacia are hemolytic. In this study, we have characterized a factor which contributes to this hemolytic activity and is secreted from B. cepacia J2315, a representative of the virulent and highly transmissible strain belonging to the recently described genomovar III grouping. Biochemical data from the described purification method for this hemolysin allows us to hypothesize that the toxin is a lipopeptide. As demonstrated for other lipopeptide toxins, the hemolysin from B. cepacia was surface active and lowered the surface tension of high-pressure liquid chromatography-grade water from 72.96 to 29.8 mN m(-1). Similar to reports for other pore-forming cytotoxins, low concentrations of the hemolysin were able to induce nucleosomal degradation consistent with apoptosis in human neutrophils and the mouse-derived macrophage-type cell line J774.2. Exposure of human neutrophils to higher concentrations of toxin resulted in increased activities of the neutrophil degranulation markers cathepsin G and elastase. Based on the results obtained in this study, we suggest a role that allows B. cepacia to thwart the immune response and a model of the events that may contribute to the severe inflammatory response in the lungs of CF patients.

Variation in flagellin genes and proteins of Burkholderia cepacia

The majority of isolates of Burkholderia cepacia, an important opportunistic pathogen associated with cystic fibrosis, can be classified into two types on the basis of flagellin protein size. Electron microscopic analysis indicates that the flagella of strains with the larger flagellin type (type I) are wider in diameter. Flagellin genes representative of both types were cloned and sequenced to design oligonucleotide primers for PCR amplification of the central variable domain of B. cepacia flagellin genes. PCR-restriction fragment length polymorphism analysis of amplified B. cepacia flagellin gene products from 16 strains enabled flagellin type classification on the basis of product size and revealed considerable differences in sequence, indicating that the flagellin gene is a useful biomarker for epidemiological and phylogenetic studies of this organism.

Siderophore production by cystic fibrosis isolates of Burkholderia cepacia

Sixty-one Burkholderia cepacia isolates from patients with cystic fibrosis (CF) and four plant isolates were screened for production of the siderophores salicylic acid (SA), pyochelin, cepabactin, and ornibactins and fingerprinted by a PCR-based randomly amplified polymorphic DNA (RAPD) method. Of the 24 RAPD types determined, 22 (92%) were associated with isolates that produced SA, 21 (87%) were associated with isolates that produced ornibactins, 15 (60%) were associated with isolates that produced pyochelin, and 3 (12%) were associated with isolates that produced cepabactin. Of the 24 RAPD types plus 2 phenotypic variants of types 1 and 9, 3 were associated with isolates that produced all four siderophores, 8 were associated with isolates that produced three siderophores, 12 were associated with isolates that produced two siderophores, and 3 were associated with isolates that produced only one siderophore. These results suggest that the numbers and types of siderophores produced by CF isolates of B. cepacia correlate with RAPD type and that SA and ornibactins are the most prevalent siderophores produced.

Agricultural use of Burkholderia (Pseudomonas) cepacia: a threat to human health?

In the past 2 decades, Burkholderia cepacia has emerged as a human pathogen causing numerous outbreaks, particularly among cystic fibrosis (CF) patients. One highly transmissible strain has spread across North America and Britain, and another between hospitalized CF and non-CF patients. Meanwhile, the organism has been developed as a biopesticide for protecting crops against fungal diseases and has potential as a bioremediation agent for breaking down recalcitrant herbicides and pesticides. However, B. cepacia is inherently resistant to multiple antibiotics; selection of strains "safe" for environmental application is not at present possible phenotypically or genotypically; molecular epidemiology and phylogenetic studies demonstrate that highly transmissible strains emerge randomly; and the organism has a capacity for rapid mutation and adaptation (facilitated by numerous insertion sequences), and a large, complex genome divided into separate chromosomes. Therefore, the widespread agricultural use of B. cepacia should be approached with caution.

Differences in chromosome number and genome rearrangements in the genus Brucella

We have studied the genomic structure and constructed the SpeI, PacI and I-CeuI restriction maps of the four biovars of the pathogenic bacterium Brucella suis. B. suis biovar 1 has two chromosomes of 2.1 Mb and 1.15 Mb, similar to those of the other Brucella species: B. melitensis, B. abortus, B. ovis and B. neotomae. Two chromosomes were also observed in the genome of B. suis biovars 2 and 4, but with sizes of 1.85 Mb and 1.35 Mb, whereas only one chromosome with a size of 3.1 Mb was found in B. suis biovar 3. We show that the differences in chromosome size and number can be explained by rearrangements at chromosomal regions containing the three rrn genes. The location and orientation of these genes confirmed that these rearrangements are due to homologous recombination at the rrn loci. This observation allows us to propose a scheme for the evolution of the genus Brucella in which the two chromosome-containing strains can emerge from an hypothetical ancestor with a single chromosome, which is probably similar to that of B. suis biovar 3. As the genus Brucella is certainly monospecific, this is the first time that differences in chromosome number have been observed in strains of the same bacterial species.

Lipopolysaccharide from Burkholderia vietnamiensis strain LMG 6999 contains two polymers identical to those present in the reference strain for Burkholderia cepacia serogroup O4

Lipopolysaccharide was isolated from strain LMG 6999 of Burkholderia vietnamiensis. Degradative and NMR spectroscopic studies established the presence of two polymeric fractions based on the following trisaccharide repeating units: I:-->3)-alpha-D-Galp-(1-->3)-beta-D-Galp-(1-->3)-beta-D-GalpNAc- (1-->; II:-->3)-alpha-D-GalpNAc-(1-->3)-beta-D-GalpNAc-(1-->4)- alpha-L-Rhap-(1-->. The same polymers have previously been found together in lipopolysaccharide from the reference strain for Burkholderia cepacia serogroup O4 and, individually, in those from B. cepacia serogroups C (I) and A (II).

Priming of neutrophil respiratory burst activity by lipopolysaccharide from Burkholderia cepacia

Neutrophil activation may play an important role in the pathogenesis of respiratory disease in Burkholderia cepacia-colonized cystic fibrosis (CF) patients. As bacterial lipopolysaccharides (LPS) are potent immunostimulatory molecules, we investigated the role of B. cepacia LPS in neutrophil activation processes. LPS extracted from a highly transmissible and virulent strain of B. cepacia (J2315) was found to increase neutrophil surface expression of the beta2 integrin, complement receptor 3, and to prime neutrophil respiratory burst responses to the neutrophil-activating agent fMet-Leu-Phe. By contrast, LPS extracted from a nonmucoid Pseudomonas aeruginosa strain isolated from a patient with CF showed little or no priming activity. As B. cepacia is currently being developed as a biocontrol agent for large-scale agricultural release, we compared LPS molecules from a range of bacterial strains for their proinflammatory ability. Priming activity was demonstrated in LPS extracts from all B. cepacia strains tested, with one environmental strain, J2552, showing the highest activity. These findings indicate (i) that B. cepacia LPS may contribute to the inflammatory nature of B. cepacia infection in CF patients, both by promoting increased neutrophil recruitment and by priming neutrophil respiratory burst responses, and (ii) that environmental strains of B. cepacia may have considerable inflammatory potential in susceptible individuals.

Structural studies of the O-specific side-chain of lipopolysaccharide from Burkholderia gladioli pv. gladioli strain NCPPB 1891

A polymeric fraction (the O-antigenic side-chain) has been isolated from the lipopolysaccharide of Burkholderia gladioli pv. gladioli strain NCPPB 1891 after mild acid hydrolysis. The components of the polymer and their molar proportions were L-Rha (1), D-Gal (1), D-Man (1), and O-acetyl (1). By means of chemical degradations and NMR studies, the repeating unit of the polymer was shown to be a linear trisaccharide of the structure shown. [formula: see text]

Genotypic analysis of Burkholderia cepacia isolates from 13 French cystic fibrosis centers

Burkholderia cepacia has been involved in outbreaks of pulmonary infection among patients with cystic fibrosis (CF), and the spread of a highly transmissible clone has been reported throughout the United Kingdom and Canada. These data prompted a DNA-based typing study of the strains recovered in French CF centers. Ninety-five isolates recovered from 71 patients attending 13 CF centers in 9 regions of France were characterized by randomly amplified polymorphic DNA (RAPD) analysis and pulsed-field gel electrophoresis (PFGE). Twenty-one genotypes were identified among the 95 isolates, and the results of RAPD and PFGE were concordant for 89 isolates (94%). Cross-colonization was demonstrated in 7 of the 13 CF centers. The investigation of serial isolates showed that most chronically colonized patients harbored a single B. cepacia strain. A geographically clustered distribution of B. cepacia genotypes was observed, except for one genotype, which was detected in four regions but was proven to be different from the genotype of the British-Canadian highly transmissible strain. The present study confirms the ability of B. cepacia to spread among CF communities in France and the importance of epidemiological surveys in the institution of prevention policies.