Trevor J. Hird

Burkholderia pseudomultivorans sp. nov., a novel Burkholderia cepacia complex species from human respiratory samples and the rhizosphere.

Eleven Burkholderia cepacia-like isolates of human clinical and environmental origin were examined by a polyphasic approach including recA and 16S rRNA sequence analysis, multilocus sequence analysis (MLSA), DNA base content determination, fatty acid methyl ester analysis, and biochemical characterization. The results of this study demonstrate that these isolates represent a novel species within the B. cepacia complex (Bcc) for which we propose the name Burkholderia pseudomultivorans. The type strain is strain LMG 26883(T) (=CCUG 62895(T)). B. pseudomultivorans can be differentiated from other Bcc species by recA gene sequence analysis, MLSA, and several biochemical tests including growth at 42°C, acidification of sucrose and adonitol, lysine decarboxylase and β-galactosidase activity, and esculin hydrolysis.

Differential Mucoid Exopolysaccharide Production by Members of the Burkholderia cepacia Complex

ABSTRACT We demonstrate that all nine species of the Burkholderia cepacia complex can express the mucoid phenotype. A survey of clinical isolates showed that strains of B. cenocepacia, the most virulent species of the complex, are most frequently nonmucoid. Additionally, isolates from patients with chronic infections can convert from mucoid to nonmucoid.

Burkholderia stagnalis sp nov and Burkholderia territorii sp nov., two novel Burkholderia cepacia complex species from environmental and human sources

Nine Burkholderia cepacia complex (Bcc) bacteria were isolated during environmental surveys for the ecological niche of Burkholderia pseudomallei, the aetiological agent of melioidosis, in the Northern Territory of Australia. They represented two multi-locus sequence analysis-based clusters, referred to as Bcc B and Bcc L. Three additional environmental and clinical Bcc B isolates were identified upon deposition of the sequences in the PubMLST database. Analysis of the concatenated nucleotide sequence divergence levels within both groups (1.4 and 1.9%, respectively) and towards established Bcc species (4.0 and 3.9%, respectively) demonstrated that the two taxa represented novel Bcc species. All 12 isolates were further characterized using 16S rRNA and recA gene sequence analysis, RAPD analysis, DNA base content determination, fatty acid methyl ester analysis and biochemical profiling. Analysis of recA gene sequences revealed a remarkable diversity within each of these taxa, but, together, the results supported the affiliation of the two taxa to the Bcc. Bcc B strains can be differentiated from most other Bcc members by the assimilation of maltose. Bcc L strains can be differentiated from other Bcc members by the absence of assimilation of N-acetylglucosamine. The names Burkholderia stagnalis sp. nov. with type strain LMG 28156(T) ( = CCUG 65686(T)) and Burkholderia territorii sp. nov. with type strain LMG 28158(T) ( = CCUG 65687(T)) are proposed for Bcc B and Bcc L bacteria, respectively.

Mucoid and Nonmucoid Burkholderia cepacia Complex Bacteria in Cystic Fibrosis Infections

RATIONALE infection with Burkholderia cepacia complex (BCC) bacteria in cystic fibrosis (CF) is associated with an unpredictable rate of pulmonary decline. Some BCC, but not others, elaborate copious mucoid exopolysaccharide, endowing them with a gross mucoid phenotype, the clinical significance of which has not been described. OBJECTIVES to determine whether there was a correlation between bacterial mucoid phenotype, as assessed in a semiquantitative manner from plate culture, and severity of disease as assessed by the rate of decline in lung function. METHODS we performed a retrospective clinical review of 100 patients with CF attending the Vancouver clinics between 1981 and 2007 and analyzed the rate of lung function decline (% predicted FEV(1)). MEASUREMENTS AND MAIN RESULTS patients infected exclusively with nonmucoid BCC had a more rapid decline in lung function (annual FEV(1) change, -8.51 ± 2.41%) than those infected with mucoid bacteria (-3.01 ± 1.09%; P < 0.05). Linear mixed-effects data modeling revealed a statistically significant inverse association between semiquantitative mucoid exopolysaccharide production and rate of decline of lung function. In vitro incubation of BCC with ceftazidime and ciprofloxacin but not meropenem caused conversion of BCC from mucoid to nonmucoid. CONCLUSIONS our data suggest an inverse correlation between the quantity of mucoid exopolysaccharide production by BCC bacteria and rate of decline in CF lung function. Certain antibiotics may induce a change in bacterial morphology that enhances their virulence. A simple in vitro test of bacterial mucoidy may be useful in predicting the rate of decline of respiratory function in CF.

Burkholderia Species Infections in Patients with Cystic Fibrosis in British Columbia, Canada. 30 Years’ Experience

RATIONALE We have been collecting Burkholderia species bacteria from patients with cystic fibrosis (CF) for the last 30 years. During this time, our understanding of their multispecies taxonomy and infection control has evolved substantially. OBJECTIVES To evaluate the long-term (30 year) epidemiology and clinical outcome of Burkholderia infection in CF, and fully define the risks associated with infection by each species. METHODS Isolates from Burkholderia-positive patients (n=107) were speciated and typed annually for each infected patient. Microbiological and clinical data were evaluated by thorough review of patient charts, and statistical analyses performed to define significant epidemiological factors. MEASUREMENTS AND MAIN RESULTS Before 1995, the majority of new Burkholderia infections were caused by epidemic clones of Burkholderia cenocepacia. After implementation of new infection control measures in 1995, Burkholderia multivorans became the most prevalent species. Survival analysis showed that patients with CF infected with B. cenocepacia had a significantly worse outcome than those with B. multivorans, and a novel finding was that, after Burkholderia infection, the prognosis for females was significantly worse than for males. CONCLUSIONS B. multivorans and B. cenocepacia have been the predominant Burkholderia species infecting people with CF in Vancouver. The implementation of infection control measures were successful in preventing new acquisition of epidemic strains of B. cenocepacia, leaving nonclonal B. multivorans as the most prevalent species. Historically, survival after infection with B. cenocepacia has been significantly worse than B. multivorans infection, and, of new significance, we show that females tend toward worse clinical outcomes.

Swimming Motility in a Longitudinal Collection of Clinical Isolates of Burkholderia cepacia Complex Bacteria from People with Cystic Fibrosis

Chronic bacterial lung infections in cystic fibrosis (CF) are the leading cause of morbidity and mortality. While a range of bacteria are known to be capable of establishing residence in the CF lung, only a small number have a clearly established link to deteriorating clinical status. The two bacteria with the clearest roles in CF lung disease are Pseudomonas aeruginosa and bacteria belonging to the Burkholderia cepacia complex (BCC). A number of common adaptations by P. aeruginosa strains to chronic lung infection in CF have been well described. Typically, initial isolates of P. aeruginosa are nonmucoid and display a range of putative virulence determinants. Upon establishment of chronic infection, subsequent isolates ultimately show a reduction in putative virulence determinants, including swimming motility, along with an acquisition of the mucoid phenotype and increased levels of antimicrobial resistance. Infections by BCC are marked by an unpredictable, but typically worse, clinical outcome. However, in contrast to P. aeruginosa infections in CF, studies describing adaptive changes in BCC bacterial phenotype during chronic lung infections are far more limited. To further enhance our understanding of chronic lung infections by BCC bacteria in CF, we assessed the swimming motility phenotype in 551 isolates of BCC bacteria from cystic fibrosis (CF) lung infections between 1981 and 2007. These data suggest that swimming motility is not typically lost by BCC during chronic infection, unlike as seen in P. aeruginosa infections. Furthermore, while we observed a statistically significant link between mucoidy and motility, we did not detect any link between motility phenotype and clinical outcome. These studies highlight the need for further work to understand the adaptive changes of BCC bacteria during chronic infection in the CF lung.

Fosmidomycin Decreases Membrane Hopanoids and Potentiates the Effects of Colistin on Burkholderia multivorans Clinical Isolates

ABSTRACT Burkholderia cepacia complex (Bcc) pulmonary infections in people living with cystic fibrosis (CF) are difficult to treat because of the extreme intrinsic resistance of most isolates to a broad range of antimicrobials. Fosmidomycin is an antibacterial and antiparasitic agent that disrupts the isoprenoid biosynthesis pathway, a precursor to hopanoid biosynthesis. Hopanoids are involved in membrane stability and contribute to polymyxin resistance in Bcc bacteria. Checkerboard MIC assays determined that although isolates of the Bcc species B. multivorans were highly resistant to treatment with fosmidomycin or colistin (polymyxin E), antimicrobial synergy was observed in certain isolates when the antimicrobials were used in combination. Treatment with fosmidomycin decreased the MIC of colistin for isolates as much as 64-fold to as low as 8 μg/ml, a concentration achievable with colistin inhalation therapy. A liquid chromatography-tandem mass spectrometry technique was developed for the accurate quantitative determination of underivatized hopanoids in total lipid extracts, and bacteriohopanetetrol cyclitol ether (BHT-CE) was found to be the dominant hopanoid made by B. multivorans. The amount of BHT-CE made was significantly reduced upon fosmidomycin treatment of the bacteria. Uptake assays with 1-N-phenylnaphthylamine were used to determine that dual treatment with fosmidomycin and colistin increases membrane permeability, while binding assays with boron-dipyrromethene-conjugated polymyxin B illustrated that the addition of fosmidomycin had no impact on polymyxin binding. This work indicates that pharmacological suppression of membrane hopanoids with fosmidomycin treatment can increase the susceptibility of certain clinical B. multivorans isolates to colistin, an agent currently in use to treat pulmonary infections in CF patients.

Comparative Genomics of Burkholderia singularis sp. nov., a Low G+C Content, Free-Living Bacterium That Defies Taxonomic Dissection of the Genus Burkholderia

Four Burkholderia pseudomallei-like isolates of human clinical origin were examined by a polyphasic taxonomic approach that included comparative whole genome analyses. The results demonstrated that these isolates represent a rare and unusual, novel Burkholderia species for which we propose the name B. singularis. The type strain is LMG 28154T (=CCUG 65685T). Its genome sequence has an average mol% G+C content of 64.34%, which is considerably lower than that of other Burkholderia species. The reduced G+C content of strain LMG 28154T was characterized by a genome wide AT bias that was not due to reduced GC-biased gene conversion or reductive genome evolution, but might have been caused by an altered DNA base excision repair pathway. B. singularis can be differentiated from other Burkholderia species by multilocus sequence analysis, MALDI-TOF mass spectrometry and a distinctive biochemical profile that includes the absence of nitrate reduction, a mucoid appearance on Columbia sheep blood agar, and a slowly positive oxidase reaction. Comparisons with publicly available whole genome sequences demonstrated that strain TSV85, an Australian water isolate, also represents the same species and therefore, to date, B. singularis has been recovered from human or environmental samples on three continents.

Whole-Genome Sequencing of Three Clonal Clinical Isolates of B. cenocepacia from a Patient with Cystic Fibrosis.

Burkholderia cepacia complex bacteria are amongst the most feared of pathogens in cystic fibrosis (CF). The BCC comprises at least 20 distinct species that can cause chronic and unpredictable lung infections in CF. Historically the species B. cenocepacia has been the most prevalent in CF infections and has been associated in some centers with high rates of mortality. Modeling chronic infection by B. cenocepacia in the laboratory is challenging and no models exist which effectively recapitulate CF disease caused by BCC bacteria. Therefore our understanding of factors that contribute towards the morbidity and mortality caused by this organism is limited. In this study we used whole-genome sequencing to examine the evolution of 3 clonal clinical isolates of B. cenocepacia from a patient with cystic fibrosis. The first isolate was from the beginning of infection, and the second two almost 10 years later during the final year of the patients’ life. These isolates also demonstrated phenotypic heterogeneity, with the first isolate displaying the mucoid phenotype (conferred by the overproduction of exopolysaccharide), while one of the later two was nonmucoid. In addition we also sequenced a nonmucoid derivative of the initial mucoid isolate, acquired in the laboratory by antibiotic pressure. Examination of sequence data revealed that the two late stage isolates shared 20 variant nucleotides in common compared to the early isolate. However, despite their isolation within 10 months of one another, there was also considerable variation between the late stage isolates, including 42 single nucleotide variants and three deletions. Additionally, no sequence differences were identified between the initial mucoid isolate and its laboratory acquired nonmucoid derivative, however transcript analysis indicated at least partial down regulation of genes involved in exopolysaccharide production. Our study examines the progression of B. cenocepacia throughout chronic infection, including establishment of sub-populations likely evolved from the original isolate, suggestive of parallel evolution. Additionally, the lack of sequence differences between two of the isolates with differing mucoid phenotypes suggests that other factors, such as gene regulation, come into play in establishing the mucoid phenotype.

Total protein extraction and 2-D gel electrophoresis methods for Burkholderia species.

The investigation of the intracellular protein levels of bacterial species is of importance to understanding the pathogenic mechanisms of diseases caused by these organisms. Here we describe a procedure for protein extraction from Burkholderia species based on mechanical lysis using glass beads in the presence of ethylenediamine tetraacetic acid and phenylmethylsulfonyl fluoride in phosphate buffered saline. This method can be used for different Burkholderia species, for different growth conditions, and it is likely suitable for the use in proteomic studies of other bacteria. Following protein extraction, a two-dimensional (2-D) gel electrophoresis proteomic technique is described to study global changes in the proteomes of these organisms. This method consists of the separation of proteins according to their isoelectric point by isoelectric focusing in the first dimension, followed by separation on the basis of molecular weight by acrylamide gel electrophoresis in the second dimension. Visualization of separated proteins is carried out by silver staining.