Advances in Phage Therapy: Targeting the Burkholderia cepacia Complex

The increasing prevalence and worldwide distribution of multidrug-resistant bacterial pathogens is an imminent danger to public health and threatens virtually all aspects of modern medicine. Particularly concerning, yet insufficiently addressed, are the members of the Burkholderia cepacia complex (Bcc), a group of at least twenty opportunistic, hospital-transmitted, and notoriously drug-resistant species, which infect and cause morbidity in patients who are immunocompromised and those afflicted with chronic illnesses, including cystic fibrosis (CF) and chronic granulomatous disease (CGD). One potential solution to the antimicrobial resistance crisis is phage therapy-the use of phages for the treatment of bacterial infections. Although phage therapy has a long and somewhat checkered history, an impressive volume of modern research has been amassed in the past decades to show that when applied through specific, scientifically supported treatment strategies, phage therapy is highly efficacious and is a promising avenue against drug-resistant and difficult-to-treat pathogens, such as the Bcc. In this review, we discuss the clinical significance of the Bcc, the advantages of phage therapy, and the theoretical and clinical advancements made in phage therapy in general over the past decades, and apply these concepts specifically to the nascent, but growing and rapidly developing, field of Bcc phage therapy.

Discovery of Ubonodin, an Antimicrobial Lasso Peptide Active against Members of the Burkholderia cepacia Complex

We report the heterologous expression, structure, and antimicrobial activity of a lasso peptide, ubonodin, encoded in the genome of Burkholderia ubonensis. The topology of ubonodin is unprecedented amongst lasso peptides, with 18 of its 28 amino acids found in the mechanically bonded loop segment. Ubonodin inhibits RNA polymerase in vitro and has potent antimicrobial activity against several pathogenic members of the Burkholderia genus, most notably B. cepacia and B. multivorans, causative agents of lung infections in cystic fibrosis patients.

Whole Genome Sequence Analysis of Burkholderia contaminans FFH2055 Strain Reveals the Presence of Putative β-Lactamases

Burkholderia contaminans is a member of the Burkholderia cepacia complex (Bcc), a pathogen with increasing prevalence among cystic fibrosis (CF) patients and the cause of numerous outbreaks due to the use of contaminated commercial products. The antibiotic resistance determinants, particularly β-lactamases, have been poorly studied in this species. In this work, we explored the whole genome sequence (WGS) of a B. contaminans isolate (FFH 2055) and detected four putative β-lactamase-encoding genes. In general, these genes have more than 93% identity with β-lactamase genes found in other Bcc species. Two β-lactamases, a class A (Pen-like, suggested name PenO) and a class D (OXA-like), were further analyzed and characterized. Amino acid sequence comparison showed that Pen-like has 82% and 67% identity with B. multivorans PenA and B. pseudomallei PenI, respectively, while OXA-like displayed strong homology with class D enzymes within the Bcc, but only 22-44% identity with available structures from the OXA family. PCR reactions designed to study the presence of these two genes revealed a heterogeneous distribution among clinical and industrial B. contaminans isolates. Lastly, bla_PenO gene was cloned and expressed into E. coli to investigate the antibiotic resistance profile and confers an extended-spectrum β-lactamase (ESBL) phenotype. These results provide insight into the presence of β-lactamases in B. contaminans, suggesting they play a role in antibiotic resistance of these bacteria.

In vitro activity of N-acetylcysteine against Stenotrophomonas maltophilia and Burkholderia cepacia complex grown in planktonic phase and biofilm

Stenotrophomonas maltophilia and Burkholderia cepacia complex (Bcc) have been increasingly recognized as relevant pathogens in hospitalized, immunocompromised and cystic fibrosis (CF) patients. As a result of complex mechanisms, including biofilm formation and multidrug resistance phenotype, S. maltophilia and Bcc respiratory infections are often refractory to therapy, and have been associated with a worse outcome in CF patients. Here we demonstrate for the first time that N-acetylcysteine (NAC), a mucolytic agent with antioxidant and anti-inflammatory properties, may exhibit antimicrobial and antibiofilm activity against these pathogens.

The antimicrobial and antibiofilm activity of high NAC concentrations, potentially achievable by topical administration, was tested against a collection of S. maltophilia (n = 19) and Bcc (n = 19) strains, including strains from CF patients with acquired resistance traits. Minimum Inhibitory Concentrations (MICs) and Minimum Bactericidal Concentrations (MBCs) ranged from 16 to 32 mg/ml and from 32 to >32 mg/ml, respectively. Sub-MIC concentrations (i.e., 0.25 × MIC) slowed down the growth kinetics of most strains. In time-kill assays, 2-day-old biofilms were more affected than planktonic cultures, suggesting a specific antibiofilm activity of NAC against these pathogens. Indeed, a dose- and time-dependent antibiofilm activity of NAC against most of the S. maltophilia and Bcc strains tested was observed, with a sizable antibiofilm activity observed also at 0.5 and 1 × MIC NAC concentrations. Furthermore, at those concentrations, NAC was also shown to significantly inhibit biofilm formation with the great majority of tested strains.

Antimicrobial activity of essential oils against multidrug-resistant clinical isolates of the Burkholderia cepacia complex

Members of the Burkholderia cepacia complex (Bcc) are an important cause of opportunistic or nosocomial infections that may be hard to treat due to a high incidence of multidrug resistance. We characterised a collection of 51 clinical isolates from this complex, assigning them to 18 sequence types using multi-locus sequence type analysis. Resistance to eight commonly used antibiotics was assessed using by using agar-dilution assays to calculate MICs and widespread and heterogeneous multidrug resistance was confirmed, with eight strains proving resistant to all antibiotics tested. Disc diffusion screening of antimicrobial activity of a range of plant essential oils against these Bcc isolates identified six oils with significant activity (lavender, lemongrass, marjoram, peppermint, tea tree and rosewood) and broth microdilution assays indicated that of these lemongrass and rosewood oils had the highest activity, with MIC50 values of 0.5% and MIC90 values of 1%. Comparison of MIC and MBC values showed that four of these six oils, including lemongrass and rosewood, were bacteriocidal rather than bacteriostatic in their effects. Qualitative analysis of the four bacteriocidal essential oils via GC/MS indicated the presence of 55 different component compounds, mostly monoterpenes. We assessed selected essential oil components as anti-Bcc agents and demonstrated that terpinen-4-ol and geraniol were effective with MICs of 0.125-0.5% (v/v) and 0.125-1% (v/v), respectively. Time-kill studies indicate that these two alcohols are effective against non-growing cells in an efflux-dependent manner. Analysis of bacterial leakage of potassium ions and 260 nm UV-absorbing material on treatment with terpinen-4-ol and geraniol suggested that the observed anti-Bcc activity was a consequence of membrane disruption. This finding was supported by a gas chromatography analysis of bacterial fatty acid methyl esters, which indicated changes in membrane fatty acid composition caused by terpinen-4-ol and geraniol. These essential oils or oil components may ultimately prove useful as therapeutic drugs, for example to treat Bcc infections in CF patients.

A 17-Year Nationwide Study of Burkholderia cepacia Complex Bloodstream Infections Among Patients in the United States Veterans Health Administration

Background

Burkholderia cepacia complex (Bcc) are a group of multidrug-resistant gram-negative bacteria rarely reported in patients without cystic fibrosis (CF) or immunocompromising conditions. We investigated Bcc bloodstream infections (BSIs) in a cohort of non-CF patients from the US Veterans Health Administration (VHA).

Methods

Using VHA databases, we identified patients with Bcc BSI at facilities nationwide from 1999 through 2015. We ascertained clinical characteristics, treatments, and outcomes and identified factors associated with 30-day mortality in logistic regression analysis.

Results

We identified 248 patients with Bcc BSI, who were of advanced age (mean, 68 years), chronically ill, and had severe disease. The most common sources were central venous catheters (41%) and pneumonia (20%). Most cases were hospital-acquired (155 [62%]) or healthcare-associated (70 [28%]). Mortality at 14, 30, and 90 days was 16%, 25%, and 36%, respectively. Trimethoprim-sulfamethoxazole (TMP-SMX) and fluoroquinolones were active against 94% and 88% of isolates, respectively. Susceptibility to ceftazidime and meropenem occurred in approximately 70% of the isolates. The most prescribed antibiotics were fluoroquinolones (35%), followed by carbapenems (20%), TMP-SMX (18.5%), and ceftazidime (11%). In regression analysis, age (OR, 1.06 [95% confidence interval {CI}, 1.02-1.10], per added year) and the Pitt bacteremia score (OR, 1.65 [95% CI, 1.44-1.94], per unit increase) were associated with higher 30-day mortality.

Conclusions

In this large cohort of BSIs caused by Bcc, cases were mostly hospital-acquired and we observed high mortality, significant resistance to ceftazidime, and limited use of TMP-SMX. These observations add to our understanding of Bcc infection in non-CF patients and highlight the need for interventions to improve their outcome.

The Role of Reactive Oxygen Species in Antibiotic-Induced Cell Death in Burkholderia cepacia Complex Bacteria

It was recently proposed that bactericidal antibiotics, besides through specific drug-target interactions, kill bacteria by a common mechanism involving the production of reactive oxygen species (ROS). However, this mechanism involving the production of hydroxyl radicals has become the subject of a lot of debate. Since the contribution of ROS to antibiotic mediated killing most likely depends on the conditions, differences in experimental procedures are expected to be at the basis of the conflicting results. In the present study different methods (ROS specific stainings, gene-expression analyses, electron paramagnetic resonance, genetic and phenotypic experiments, detection of protein carbonylation and DNA oxidation) to measure the production of ROS upon antibiotic treatment in Burkholderia cepacia complex (Bcc) bacteria were compared. Different classes of antibiotics (tobramycin, ciprofloxacin, meropenem) were included, and both planktonic and biofilm cultures were studied. Our results indicate that some of the methods investigated were not sensitive enough to measure antibiotic induced production of ROS, including the spectrophotometric detection of protein carbonylation. Secondly, other methods were found to be useful only in specific conditions. For example, an increase in the expression of OxyR was measured in Burkholderia cenocepacia K56-2 after treatment with ciprofloxacin or meropenem (both in biofilms and planktonic cultures) but not after treatment with tobramycin. In addition results vary with the experimental conditions and the species tested. Nevertheless our data strongly suggest that ROS contribute to antibiotic mediated killing in Bcc species and that enhancing ROS production or interfering with the protection against ROS may form a novel strategy to improve antibiotic treatment.

[ANTIBIOTICS SENSITIVITY OF STAPHYLOCOCCUS AUREUS, PSEUDOMONAS AERUGINOSA AND BACTERIA OF BURKHOLDERIA CEPACIA COMPLEX, PERSISTING IN LUNGS OF PATIENTS WITH MUCOVISCIDOSIS (MV)]

AIM

Study the spectrum of resistance to antibiotics and its variability of Staphylococcus aureus, Pseudomonas aeruginosa and Burkholderia cepacia complex (BCC), persisting in lungs of MV patients.

MATERIALS AND METHODS

312 strains of S. aureus, 213 strains of P. aeruginosa, 186 strains of BCC were studied. Monitoring of antibiotics sensitivity was carried out in strains, isolated from 30 patients with chronic S. aureus infection, from 22 patients with chronic BCC infection and from 21 patients with chronic pseudomonas infection. Interval of monitoring was from 14 days to 5 years 7 months.

RESULTS

Study of S. aureus, P. aeruginosa and BCC strains has shown, that 35 and 33.3% of cases of staphylococcus infection, 37 and 46% of pseudomonas infection in children and adults, respectively, 100% of BCC infections were determined by multi-resistant clones. Study of genotypically identical strains, isolated from a single patient at different stages, has shown a change in antibiotics sensitivity as a result of persistence.

CONCLUSION

Persisent infection of lungs in patients with MV is determined: by exchanging clones with varying antibiotics sensitivity or prolonged circulation of a single clone with a high degree of phenotypical and genotypical variability, that determine alteration of seeding of sensitive and resistant strains from the same patient during monitoring. This confirms the necessity of study of antibiotics sensitivity of strains for prescription of antibacterial therapy.

Clonality and Antimicrobial Susceptibility of Burkholderia cepacia complex Isolates Collected from Cystic Fibrosis Patients during 1998-2013 in Bern, Switzerland

For the first time, we analyzed the clonality and susceptibility of Burkholderia cepacia complex isolates (n=55) collected during 1998-2013 from 44 Swiss cystic fibrosis (CF)-patients. B. cenocepacia (n=28) and B. multivorans (n=14) were mainly of sequence type (ST) 833 and ST874, respectively; B. contaminans isolates were of ST102. Overall, the following MIC50/90s (mg/l) were obtained: piperacillin/tazobactam (≤ 4/≥ 128), ticarcillin/clavulanate (≥ 256/≥256), ceftazidime (2/≥ 32), aztreonam (16/≥ 32), meropenem (2/8), tobramycin (8/≥ 16), minocycline (≤ 1/16), levofloxacin (≤ 0.5/≥ 16), and trimethoprim/sulfamethoxazole (≤ 0.5/4). This is the first survey providing information on the clonality of Bcc detected in Switzerland. Species identification and antimicrobial susceptibility tests should always be routinely performed to adapt more targeted therapies.

Garlic revisited: antimicrobial activity of allicin-containing garlic extracts against Burkholderia cepacia complex

The antimicrobial activities of garlic and other plant alliums are primarily based on allicin, a thiosulphinate present in crushed garlic bulbs. We set out to determine if pure allicin and aqueous garlic extracts (AGE) exhibit antimicrobial properties against the Burkholderia cepacia complex (Bcc), the major bacterial phytopathogen for alliums and an intrinsically multiresistant and life-threatening human pathogen. We prepared an AGE from commercial garlic bulbs and used HPLC to quantify the amount of allicin therein using an aqueous allicin standard (AAS). Initially we determined the minimum inhibitory concentrations (MICs) of the AGE against 38 Bcc isolates; these MICs ranged from 0.5 to 3% (v/v). The antimicrobial activity of pure allicin (AAS) was confirmed by MIC and minimum bactericidal concentration (MBC) assays against a smaller panel of five Bcc isolates; these included three representative strains of the most clinically important species, B. cenocepacia. Time kill assays, in the presence of ten times MIC, showed that the bactericidal activity of AGE and AAS against B. cenocepacia C6433 correlated with the concentration of allicin. We also used protein mass spectrometry analysis to begin to investigate the possible molecular mechanisms of allicin with a recombinant form of a thiol-dependent peroxiredoxin (BCP, Prx) from B. cenocepacia. This revealed that AAS and AGE modifies an essential BCP catalytic cysteine residue and suggests a role for allicin as a general electrophilic reagent that targets protein thiols. To our knowledge, we report the first evidence that allicin and allicin-containing garlic extracts possess inhibitory and bactericidal activities against the Bcc. Present therapeutic options against these life-threatening pathogens are limited; thus, allicin-containing compounds merit investigation as adjuncts to existing antibiotics.

The contribution of antibiotic resistance mechanisms in clinical Burkholderia cepacia complex isolates: an emphasis on efflux pump activity

Due to the limited information of the contribution of various antibiotic resistance mechanisms in clinical Burkholderia cepacia complex isolates, Antibiotic resistance mechanisms, including integron analysis, identification of quinolone resistance-determining region mutations, measurement of efflux pump activity, and sequence analysis of efflux pump regulators, were investigated in 66 clinical B. cepacia complex isolates. Species were identified via recA-RFLP and MALDI-TOF. Four genomovars were identified by recA-RFLP. B. cenocepacia (genomovar III) was the most prevalent genomovar (90.1%). Most isolates (60/66, 90.9%) were correctly identified by MALDI-TOF analysis. Clonal relatedness determined by PFGE analysis revealed 30 pulsotypes, including two major pulsotypes that comprised 22.7% and 18.2% of the isolates, respectively. Seventeen (25.8%) isolates harboured class 1 integron with various combinations of resistance genes. Among six levofloxacin-resistant isolates, five had single-base substitutions in the gyrA gene and three demonstrated efflux pump activities. Among the 42 isolates exhibiting resistance to at least one antimicrobial agent, 94.4% ceftazidime-resistant isolates (17/18) and 72.7% chloramphenicol-resistant isolates (16/22) demonstrated efflux pump activity. Quantitation of efflux pump RNA level and sequence analysis revealed that over-expression of the RND-3 efflux pump was attributable to specific mutations in the RND-3 efflux pump regulator gene. In conclusion, high-level expression of efflux pumps is prevalent in B. cepacia complex isolates. Mutations in the RND-3 efflux pump regulator gene are the major cause of efflux pump activity, resulting in the resistance to antibiotics in clinical B. cepacia complex isolates.

[Advances in virulence determinants in Burkholderia cepacia complex--a review]

Most members of the Burkholderia cepacia complex (Bcc) are important human opportunistic pathogens. Although progress has been achieved on the taxonomy and molecular identification of these bacteria, the molecular mechanisms of Bcc pathogenicity remain unclear and little development is made for new therapeutic agents. As Bcc is resistant to many common clinically-relevant antibiotics, revealing its virulence determinants is therefore very important to develop novel antibiotics or alternative anti-infective therapies. In this review, we summarize current advances in principal virulence determinants, limitations and genetic tools for studies of pathogenesis of Bcc. We primarily focus on key pathogenicity factors, including innate resistance to antibiotics, protein secretion system, and quorum-sensing systems.

Burkholderia cepacia complex infection in an Adult Cystic Fibrosis unit in Madrid

INTRODUCTION

Burkholderia cepacia complex have emerged as significant pathogens in cystic fibrosis (CF) patients due to the risk of cepacia syndrome and the innate multi-resistance of the microorganisms to antibiotics. The aim of this study was to describe the antimicrobial susceptibility profiles, the genotypes and subtypes of BCC, and the clinical evolution of CF patients with BCC.

METHODS

The lung function and Brasfield and Shwachman score were assessed in 12 patients. BCC were identified and susceptibility was studied by MicroScan (Siemens). Species and genospecies of BCC were confirmed by molecular methods in a Reference Centre (Majadahonda).

RESULTS

BCC were identified in 12 of 70 patients (17.1%) over a ten year period. The mean age to colonization by BCC was 24.4 years (SD: 7.71). B. cenocepacia was isolated in 4 patients (33.3%), B. contaminans was isolated in 3 patients (25%), both B. vietnamiensis and B. stabilis were isolated in 2 patients (16.7%), and B. cepacia, B. multivorans and B. late were isolated in one patient (8.3%). Among the B. cenocepacia, subtype IIIa was identified in two strains, and subtype IIIb was identified in the other two strains. There was susceptibility to meropenem in 90% of BCC, 80% to cotrimoxazole, 60% to minocycline, 50% to ceftazidime, and 40% to levofloxacin.

CONCLUSIONS

B. cenocepacia was the most prevalent species among the BCC isolated in CF adult patients, and subtypes IIIa and IIIb were identified in the 50% of the strains. Meropenem and cotrimoxazole showed the best activity.

[An opportunistic pathogen frequently isolated from immunocompromised patients: Burkholderia cepacia complex]

Burkholderia cepacia complex is a group of 17 closely related species. For a long time B.cepacia complex is believed to be only a plant pathogen but later it has emerged as an important opportunistic pathogen causing morbidity and mortality in hospitalized patients. B.cepacia complex particularly causes bacteraemia/sepsis, septic arthritis, osteomyelitis, meningitis, peritonitis, urinary and respiratory tract infections. Patients with cystic fibrosis or chronic granulomatous disease are predisposed to B.cepacia complex infections. B.cepacia complex can survive for a long period of time and can easily multiply in aqueous environments such as disinfectant agents and intravenous fluids used in hospitals. Patients may acquire B.cepacia complex either from the environment or through patient-to-patient transmission. It has always been a tedious task for routine microbiology laboratory to identify B.cepacia complex. In these laboratories, the identification of B.cepacia complex isolates is generally performed using a combination of selective media, conventional biochemical analysis and/or commercial systems. Three media commonly used for isolation of B.cepacia complex are as follows: the Pseudomonas cepacia agar, the oxidation-fermentation based polymyxin bacitracin lactose agar, and more recently the B.cepacia selective agar. Members of the B.cepacia complex can be identified by available commercial tests, such as API 20NE, Phoenix, MicroScan or VITEK. Molecular techniques are useful for confirmation of phenotypic identification and discrimination beyond the species-level. B.cepacia complex is intrinsically resistant to antimicrobial agents such as aminoglycosides, first- and second-generation cephalosporins, antipseudomonal penicillins and polymyxins. B.cepacia complex bacteria often develop resistance to beta-lactams due to presence of inducible chromosomal beta-lactamases and altered penicillin- binding proteins. Antibiotic efflux pumps in B.cepacia complex bacteria mediate resistance to chloramphenicol, trimethoprim and fluoroquinolones. Under antimicrobial pressure, resistance can quickly develop to all susceptible antimicrobials. In this review, the classification and microbiological features of B.cepacia complex, mechanisms of virulence and pathogenesis, epidemiological properties, clinical spectrum, laboratory diagnosis, antimicrobial resistance and treatment, prevention and control measures were summarized.

Occurrence and antibiotic susceptibility profiles of Burkholderia cepacia complex in coastal marine environment

During an environmental study of bacterial resistance to antibiotics in coastal waters of the Kaštela Bay, Adriatic Sea, Croatia, 47 Burkholderia cepacia complex (Bcc) isolates were recovered from seawater and mussel (Mytilus galloprovincialis) samples. All isolates showed multiple antibiotic resistance. Among the isolates, two Burkholderia cenocepacia isolates produced chromosomally encoded TEM-116 extended-spectrum β-lactamase (ESBL). Analysis of outer membrane proteins revealed that decreased expression of a 36-kDa protein could be associated with a high level of β-lactam resistance in both isolates. Phenotypic study of efflux system also indicated an over-expression of Resistance-Nodulation-Cell Division (RND) efflux-mediated mechanism in one of the isolates. This study demonstrated the presence of Bcc in seawater and M. galloprovincialis, which gives evidence that coastal marine environment, including mussels, could be considered as a reservoir for Bcc species. Detection of ESBL-encoding genes indicates the potential role of these bacteria in the maintenance and dispersion of antibiotic resistance genes.

[Detection of Burkholderia cepacia complex strains in the University Hospital Olomouc]

BACKGROUND

The aim was to assess the epidemiology of Burkholderia cepacia complex strains isolated at the Department of Microbiology, Faculty of Medicine and Dentistry, Palacky University and University Hospital Olomouc, determine the most frequent strains and confirm or rule out potential clonal spread of the strains.

MATERIAL AND METHODS

Over a period of eight months, all strains classified as Burkholderia cepacia complex were collected. Susceptibility to selected antimicrobial agents was determined and adequate molecular genetic methods were used to assess their genetic relationship.

RESULTS

A total of 52 isolates were tested, with the most frequent (88.5 %) being genomovar II (Burkholderia multivorans). More than 46 % of them were genetically related; 58.3 % of them were detected in intensive care units. All isolates were highly resistant to antimicrobial agents. In four cases, deaths associated with Burkholderia multivorans infection were reported.

CONCLUSION

It may be assumed that genetically related strains of Burkholderia multivorans spread from the hospital setting. As yet, the source of infection has not been determined and further investigations are needed.

Characterization of the volatile profile of Antarctic bacteria by using solid-phase microextraction-gas chromatography-mass spectrometry

Bacteria belonging to the Burkholderia cepacia complex (Bcc) are significant pathogens in Cystic Fibrosis (CF) patients and are resistant to a plethora of antibiotics. In this context, microorganisms from Antarctica are interesting because they produce antimicrobial compounds inhibiting the growth of other bacteria. This is particularly true for bacteria isolated from Antarctic sponges. The aim of this work was to characterize a set of Antarctic bacteria for their ability to produce new natural drugs that could be exploited in the control of infections in CF patients by Bcc bacteria. Hence, 11 bacterial strains allocated to different genera (e.g., Pseudoalteromonas, Arthrobacter and Psychrobacter) were tested for their ability to inhibit the growth of 21 Bcc strains and some other human pathogens. All these bacteria completely inhibited the growth of most, if not all, Bcc strains, suggesting a highly specific activity toward Bcc strains. Experimental evidences showed that the antimicrobial compounds are small volatile organic compounds, and are constitutively produced via an unknown pathway. The microbial volatile profile was obtained by SPME-GC-MS within the m/z interval of 40-450. Solid phase micro extraction technique affords the possibility to extract the volatile compounds in head space with a minimal sample perturbation. Principal component analysis and successive cluster discriminant analysis was applied to evaluate the relationships among the volatile organic compounds with the aim of classifying the microorganisms by their volatile profile. These data highlight the potentiality of Antarctic bacteria as novel sources of antibacterial substances to face Bcc infections in CF patients.

Resistance of the Burkholderia cepacia complex to fosmidomycin and fosmidomycin derivatives

The Burkholderia cepacia complex (BCC) is a group of 17 closely related opportunistic pathogens that are able to infect the respiratory tract of cystic fibrosis patients. BCC bacteria are intrinsically resistant to many antibiotics and are therefore difficult to eradicate. Fosmidomycin could be a new therapeutic agent to treat BCC infections as it inhibits 1-deoxy-d-xylulose-5-phosphate reductoisomerase (Dxr), a key enzyme in the non-mevalonate pathway essential in BCC bacteria for isoprenoid synthesis. In this study, the antimicrobial activity of fosmidomycin and eight fosmidomycin derivatives towards 40 BCC strains was investigated. All BCC strains were resistant to fosmidomycin, although addition of glucose-6-phosphate reduced the minimum inhibitory concentration values of FR900098, the fosmidomycin acetyl derivative, from 512 mg/L to 64 mg/L for Burkholderia multivorans and B. cepacia. This enhanced activity was linked to increased expression of the genes involved in glycerol-3-phosphate transport, which appears to be the only route for fosmidomycin import in BCC bacteria. Furthermore, upregulation of a fosmidomycin resistance gene (fsr) encoding an efflux pump was observed during fosmidomycin and FR900098 treatment. These results strongly suggest that the observed resistance in BCC bacteria is due to insufficient uptake accompanied by fosmidomycin and FR900098 efflux.

Efflux pumps may play a role in tigecycline resistance in Burkholderia species

The purpose of this study was to investigate the role of multidrug resistance efflux pumps in relation to decreased susceptibility to tigecycline in clinical isolates of Burkholderia cepacia complex (BCC). The role of efflux pumps was analysed using the efflux pump inhibitor (EPI) MC-207,110. Minimum inhibitory concentrations (MICs) were determined for each strain against tigecycline alone and in the presence of 64 mg/L MC-207,110. The effect of efflux pump inhibition on the susceptibility of BCC isolates to tigecycline was assessed by a checkerboard titration assay. Ala-Nap uptake assay was performed to determine efflux pump activity in different strains. The checkerboard titration assay showed that the MIC decreased with increasing concentrations of EPI. MICs for tigecycline in the clinical isolates ranged between 8 mg/L and 32 mg/L, whereas in the presence of MC-207,110, MICs decreased significantly (range <0.125-1.0mg/L; 16 to >256 times reduction). Efflux pump activity was shown to be greatest in strains with the highest MIC and vice versa. In conclusion, BCC possess efflux pumps that influence their resistance to tigecycline. Use of an inhibitor of these pumps restored sensitivity to the antibiotic. Therefore, a combination of tigecycline and EPI to augment its efficacy may present an attractive therapeutic option.

A decade of Burkholderia cenocepacia virulence determinant research

The Burkholderia cepacia complex (Bcc) is a group of genetically related environmental bacteria that can cause chronic opportunistic infections in patients with cystic fibrosis (CF) and other underlying diseases. These infections are difficult to treat due to the inherent resistance of the bacteria to antibiotics. Bacteria can spread between CF patients through social contact and sometimes cause cepacia syndrome, a fatal pneumonia accompanied by septicemia. Burkholderia cenocepacia has been the focus of attention because initially it was the most common Bcc species isolated from patients with CF in North America and Europe. Today, B. cenocepacia, along with Burkholderia multivorans, is the most prevalent Bcc species in patients with CF. Given the progress that has been made in our understanding of B. cenocepacia over the past decade, we thought that it was an appropriate time to review our knowledge of the pathogenesis of B. cenocepacia, paying particular attention to the characterization of virulence determinants and the new tools that have been developed to study them. A common theme emerging from these studies is that B. cenocepacia establishes chronic infections in immunocompromised patients, which depend more on determinants mediating host niche adaptation than those involved directly in host cells and tissue damage.

In vitro activity of temocillin against planktonic and sessile Burkholderia cepacia complex bacteria

Burkholderia cepacia complex (Bcc) bacteria are opportunistic respiratory pathogens which are particularly difficult to eradicate from the lungs of cystic fibrosis (CF) patients because of their innate resistance to antimicrobials and their capacity to form biofilms. The goal of the present study was to evaluate the bacteriostatic and bactericidal activities of temocillin against planktonic and sessile Bcc bacteria. 37 strains belonging to 17 Bcc species were tested. 75.7% of the strains were susceptible when grown planktonically (minimal inhibitory concentration <16 μg/ml). The minimal bactericidal concentrations were higher than 128 μg/ml for most strains. No remarkable differences in resistance between exponentially growing planktonic cells and 4 h old biofilms were observed: when grown in a biofilm, 59.5% of the strains were susceptible. After treating 24 h biofilms with a concentration of 10×MIC, only a minor reduction was seen in the number of sessile cells, indicating a limited bactericidal activity against biofilms. Our data indicate that temocillin has a good bacteriostatic in vitro activity against planktonic and 4 h old biofilms, but seems of limited use to eradicate 24 h old biofilms.

Antibiotic resistance patterns and SDS-PAGE protein profiles of Burkholderia cepacia complex isolates from nosocomial and environmental sources in Venezuela

BACKGROUND

Antibiotic resistance and SDS-PAGE protein patterns were determined in nosocomial and environmental isolates of the Burkholderia cepacia complex to assess similarities between them and to identify common protein bands that could be associated with resistance to certain antimicrobial agents.

MATERIAL/METHODS

Antibiotic resistance patterns were determined by the disk diffusion method on Mueller-Hinton medium and minimum inhibitory concentrations were obtained by the dilution method on agar. Electrophoresis of whole-cell protein extracts and purified external membrane proteins were performed by SDS-PAGE. Based on resistance to nine antibiotics and the presence or absence of specific protein bands, dendrograms were constructed by the unweighted pair-group using the average linkage clustering method.

RESULTS

Both environmental and nosocomial Bcc isolates showed resistance to multiple antibiotics; however, clinical isolates demonstrated two times higher resistance levels than environmental isolates. The Dice index similarity coefficients between environmental and nosocomial strains ranged from 72% to 91.4%. Comparative analysis between common protein bands and antibiotic resistance patterns revealed close association of Mr 135, 76, 72, 53, and 50 kDa with imipenem and aztreonam, Mr 53 and 31 kDa with trimethoprim/sulfamethoxazole, and Mr 50 kDa with ceftazidime resistance.

CONCLUSIONS

1. The environmental and nosocomial Bcc isolates showed a high degree of similarity in their protein profiles. 2. Three common protein bands, i.e. Mr of 31, 50, and 53 kDa, detected in the Bcc isolates from both clinical and natural sources could be associated with resistance to the antimicrobial agents trimethoprim/sulfamethoxazole, ceftazidime, and aztreonam, respectively.

Comparison of antibiotic susceptibility of Burkholderia cepacia complex organisms when grown planktonically or as biofilm in vitro

This study determined the antibiotic susceptibility of planktonic and biofilm cultures of Burkholderia cepacia complex organisms, a group of highly problematic pathogens associated with cystic fibrosis patients. The biofilm inhibitory concentrations were considerably higher than the corresponding minimum inhibitory concentrations for meropenem and piperacillin-tazobactam. However, tobramycin and amikacin were efficacious against both biofilm and planktonic cultures. Overall this study showed that biofilm susceptibility testing might be more clinically appropriate for determining antibiotic therapy for Burkholderia cepacia complex infections in cystic fibrosis patients.

The effect of recombinant human lactoferrin on growth and the antibiotic susceptibility of the cystic fibrosis pathogen Burkholderia cepacia complex when cultured planktonically or as biofilms

OBJECTIVES

The cystic fibrosis (CF) pathogen Burkholderia cepacia complex (Bcc) is innately resistant to antibiotics and the development of effective therapeutic strategies to treat these infections is a major challenge. The objectives of this study were to investigate the effects of recombinant human lactoferrin (rHL) on planktonic and biofilm cultures of Bcc organisms and to establish whether lactoferrin alters the susceptibility of these cultures to a range of antibiotic therapies.

METHODS

Planktonic and biofilm cultures of strains representative of three species of Bcc, Burkholderia multivorans, Burkholderia cenocepacia and Burkholderia dolosa, were exposed to 0-900 mg/L lactoferrin over 0-48 h. Growth was determined using both spectrophotometric and plate counting methods. The ability of these strains to form and develop biofilms in vitro was also examined. Antimicrobial susceptibility in the presence/absence of lactoferrin was assessed using conventional MICs and a modified method was used to determine biofilm susceptibility to various antibiotics.

RESULTS

We found that physiological concentrations of lactoferrin inhibited the growth of both planktonic and biofilm cultures of Bcc in vitro. The addition of lactoferrin to rifampicin enhanced the antibiotic susceptibility of the Bcc strains when grown planktonically and as biofilms.

CONCLUSIONS

The present study demonstrates the growth inhibitory and antibiofilm activity of rHL against different species of Bcc. Furthermore, the enhanced susceptibility of both planktonic and biofilm cultures to rifampicin in the presence of lactoferrin offers the potential for novel uses of antibiotics in combination with lactoferrin to treat Bcc infections in CF patients.

Infection with Burkholderia cepacia complex bacteria and pulmonary exacerbations of cystic fibrosis

BACKGROUND

Studies have shown that cystic fibrosis (CF) patients who are chronically infected with Burkholderia cepacia complex bacteria may potentially acquire new strains of B cepacia. Our objective was to determine whether pulmonary exacerbations of CF are associated with acquisition of new B cepacia strains or with B cepacia strain replacement.

METHODS

Thirty-six patients from seven centers who were chronically infected with B cepacia complex bacteria were prospectively followed up over a 38-month period. Patients had sputum cultures performed every 3 months while clinically stable and at the time of a pulmonary exacerbation. Each B cepacia complex isolate was speciated by polymerase chain reaction amplification of the recA gene to determine species status and was genotyped by pulsed-field gel electrophoresis to determine strain type.

RESULTS

Thirty-five of 36 patients (97%) had chronic infection with Burkholderia cenocepacia III-A during clinical stability. All 36 patients maintained the same species and strain of B cepacia complex at the time of exacerbation as was found during clinical stability. B cepacia complex isolates retrieved during exacerbations were significantly less susceptible to ciprofloxacin, chloramphenicol, piperacillin, meropenem, and tobramycin compared to isolates retrieved from the same patients during clinical stability.

CONCLUSION

Adult CF patients infected with B cenocepacia maintain the same strain of B cenocepacia during exacerbations; pulmonary exacerbations are not caused by acquisition of a new B cepacia species or strain. B cepacia isolates retrieved during exacerbations may be more resistant to antibiotics.

Evolving epidemiology of Pseudomonas aeruginosa and the Burkholderia cepacia complex in cystic fibrosis lung infection

The morbidity and mortality of patients with cystic fibrosis (CF) is primarily determined by chronic and debilitating lung infections caused by a surprisingly narrow spectrum of bacterial pathogens. Pseudomonas aeruginosa is by far the most prevalent life-threatening CF pathogen. In the absence of aggressive early therapy, it infects the majority of adult patients and determines long-term survival. The epidemiology of CF pulmonary infections continues to evolve. Amongst the most recent CF pathogens to have emerged are a group of closely related bacteria, known as the Burkholderia cepacia complex. These organisms are a particular challenge due to inherent antibiotic resistance, the potential for patient-to-patient spread, and the risk of ‘cepacia syndrome’, a rapid fulminating pneumonia sometimes accompanied by bacteremia. Strict cross-infection control was prompted by early epidemiological experience of the B. cepacia complex and is essential in the management of all CF pathogens.

Characterization of SodC, a periplasmic superoxide dismutase from Burkholderia cenocepacia

Burkholderia cenocepacia is a gram-negative, non-spore-forming bacillus and a member of the Burkholderia cepacia complex. B. cenocepacia can survive intracellularly in phagocytic cells and can produce at least one superoxide dismutase (SOD). The inability of O2- to cross the cytoplasmic membrane, coupled with the periplasmic location of Cu,ZnSODs, suggests that periplasmic SODs protect bacteria from superoxide that has an exogenous origin (for example, when cells are faced with reactive oxygen intermediates generated by host cells in response to infection). In this study, we identified the sodC gene encoding a Cu,ZnSOD in B. cenocepacia and demonstrated that a sodC null mutant was not sensitive to a H2O2, 3-morpholinosydnonimine, or paraquat challenge but was killed by exogenous superoxide generated by the xanthine/xanthine oxidase method. The sodC mutant also exhibited a growth defect in liquid medium compared to the parental strain, which could be complemented in trans. The mutant was killed more rapidly than the parental strain was killed in murine macrophage-like cell line RAW 264.7, but killing was eliminated when macrophages were treated with an NADPH oxidase inhibitor. We also confirmed that SodC is periplasmic and identified the metal cofactor. B. cenocepacia SodC was resistant to inhibition by H2O2 and was unusually resistant to KCN for a Cu,ZnSOD. Together, these observations establish that B. cenocepacia produces a periplasmic Cu,ZnSOD that protects this bacterium from exogenously generated O2- and contributes to intracellular survival of this bacterium in macrophages.

[Biofilm formation by strains of Burkholderia cepacia complex in dependence of their phenotypic and genotypic characteristics]

Biofilm formation was studied in 54 strains of Burkholderia cepacia complex isolated in 7 Moscow hospitals. 80% of strains (biofilm groups I and II) had the capacity to biofilm formation and only 16.7% of strains (group III) were not capable to biofilm formation. Molecular genetic methods allowed to identify one of the epidemic markers (CBL, IS hybrid sequence, Burkholderia Cepacia Epidemic Strain Marker - BCESM) in 46.7, 23.3, and 33.3% of strains from group I, II, and III respectively. Gene cepR from the Quorum Sensing system was identified in three biofilm groups in nearly equal frequency (92.3, 96.2 and 100% for group I, II, and III respectively), whereas cepl gene was found more often in group I (76.9%) and II (65.4%). Strains from all three groups had protease and lipase activity and 13.3% of group I strains had chitinolytic activity. B. cepacia strains from group I produced hemolysin in 33.3% of cases, from group II--in 26.6%, and from group III--in 11.1% of cases. The majority of Moscow hospital strains of B. cepacia complex were identified as B. cenocepacia (genomovar III, group A). RAPD-PCR method enabled to differentiate isolated strains into several genotypic variants. 13.3% of strains from group I were susceptible to imipenem/ciprofloxacin, as well as 33.3% of isolates from group II and 44.4% of isolates from group III.

Emerging cystic fibrosis pathogens: incidence and antimicrobial resistance

We examined the frequency of isolation and the antimicrobial resistance of Burkholderia cepacia complex, Stenotrophomonas maltophilia and Achromobacter xylosoxidans in cystic fibrosis patients from 2000 to 2004. Strains susceptibility to tobramycin, piperacillin/tazobactam, imipenem, gentamicin, ciprofloxacin and ceftazidime was determined by disc diffusion assay. B. cepacia complex showed a very high resistance also to ciprofloxacin reaching 100% in 2004. S. maltophilia and A. xvylosoxidans showed high rates of antimicrobial resistance both aminoglycoside and ciprofloxacin. It is very important to monitor the percentage of isolation of these species over time to verify strains resistance to antibiotics and also to test new combinations of antimicrobial agents.

Antimicrobial susceptibility and synergy studies of Burkholderia cepacia complex isolated from patients with cystic fibrosis

Susceptibility (18 antimicrobial agents including high-dose tobramycin) and checkerboard synergy (23 combinations) studies were performed for 2,621 strains of Burkholderia cepacia complex isolated from 1,257 cystic fibrosis patients. Minocycline, meropenem, and ceftazidime were the most active, inhibiting 38%, 26%, and 23% of strains, respectively. Synergy was rarely noted (range, 1% to 15% of strains per antibiotic combination).

Efflux pump genes of the resistance-nodulation-division family in Burkholderia cenocepacia genome

Background

Burkholderia cenocepacia is recognized as opportunistic pathogen that can cause lung infections in cystic fibrosis patients. A hallmark of B. cenocepacia infections is the inability to eradicate the organism because of multiple intrinsic antibiotic resistance. As Resistance-Nodulation-Division (RND) efflux systems are responsible for much of the intrinsic multidrug resistance in Gram-negative bacteria, this study aims to identify RND genes in the B. cenocepacia genome and start to investigate their involvement into antimicrobial resistance.

Results

Genome analysis and homology searches revealed 14 open reading frames encoding putative drug efflux pumps belonging to RND family in B. cenocepacia J2315 strain.

By reverse transcription (RT)-PCR analysis, it was found that orf3, orf9, orf11, and orf13 were expressed at detectable levels, while orf10 appeared to be weakly expressed in B. cenocepacia. Futhermore, orf3 was strongly induced by chloramphenicol. The orf2 conferred resistance to fluoroquinolones, tetraphenylphosphonium, streptomycin, and ethidium bromide when cloned and expressed in Escherichia coli KAM3, a strain lacking the multidrug efflux pump AcrAB. The orf2-overexpressing E. coli also accumulate low concentrations of ethidium bromide, which was restored to wild type level in the presence of CCCP, an energy uncoupler altering the energy of the drug efflux pump.

Conclusion

The 14 RND pumps gene we have identified in the genome of B. cenocepacia suggest that active efflux could be a major mechanism underlying antimicrobial resistance in this microorganism. We have characterized the ORF2 pump, one of these 14 potential RND efflux systems. Its overexpression in E. coli conferred resistance to several antibiotics and to ethidium bromide but it remains to be determined if this pump play a significant role in the antimicrobial intrinsic resistance of B. cenocepacia. The characterization of antibiotic efflux pumps in B. cenocepacia is an obligatory step prior to the design of specific, potent bacterial inhibitors for the improved control of infectious diseases. Consequently, the topic deserves to be further investigated and future studies will involve systematic investigation on the function and expression of each of the RND efflux pump homologs.

Burkholderia cenocepacia utilizes ferritin as an iron source

Burkholderia cenocepacia is a member of the Burkholderia cepacia complex, a group of genetically similar species that inhabit a number of environmental niches, including the lungs of patients with cystic fibrosis (CF). To colonize the lung, this bacterium requires a source of iron to satisfy its nutritional requirements for this important metal. Because of the high potential for damage in lung tissue resulting from oxygen-iron interactions, this metal is sequestered by a number of mechanisms that render it potentially unavailable to invading micro-organisms. Such mechanisms include the intracellular and extracellular presence of the iron-binding protein ferritin. Ferritin has a highly stable macromolecular structure and may contain up to 4500 iron atoms per molecule. To date, there has been no known report of a pathogenic bacterial species that directly utilizes iron sequestered by this macromolecule. To examine the ability of ferritin to support growth of B. cenocepacia J2315, iron-deficient media were supplemented with different concentrations of ferritin and the growth kinetics characterized over a 40 h period. The results indicated that B. cenocepacia J2315 utilizes iron bound by ferritin. Further studies examining the mechanisms of iron uptake from ferritin indicated that iron utilization results from a proteolytic degradation of this otherwise stable macromolecular structure. Since it is known that the ferritin concentration is significantly higher in the CF lung than in healthy lungs, this novel iron-acquisition mechanism may contribute to infection by B. cenocepacia in people with CF.

Molecular epidemiology and antibiotic susceptibility of Burkholderia cepacia-complex isolates from an Italian cystic fibrosis centre

In order to further understanding of how different isolates of Burkholderia cepacia complex persist, spread and cause disease, B. cepacia-complex isolates from 60 patients attending the Cystic Fibrosis Centre of Verona, Italy, between 1997 and 2002 were analyzed. Strains were examined for species, presence of putative epidemic and virulence markers (i.e., cblA and the B. cepacia epidemic-strain marker [BCESM]), genetic relatedness and antibiotic susceptibility. Forty-five percent of patients were infected with B. cenocepacia recA subgroup B, 28% with B. cenocepacia recA subgroup A, 5% with B. multivorans and 5% with B. cepacia. No isolate carried cblA but 35% of B. cenocepacia and one of B. cepacia carried the BCESM transmissibility marker. Pulsed-field gel electrophoresis (PFGE) identified 40 types; 22 of these corresponded to sporadic isolates and 18 to clusters of identical or genetically related strains. Piperacillin, ceftazidime and piperacillin-tazobactam were the most active antibiotics (43.3, 31.1 and 35.5% of resistance, respectively). These results confirm the prevalence of B. cenocepacia in cystic fibrosis patients with rapid clinical deterioration and in those with stable cases of infection. The rates of multiple-source and cross infection were relatively low.

In vitro activity of doripenem (S-4661) against multidrug-resistant gram-negative bacilli isolated from patients with cystic fibrosis

Doripenem 50% inhibitory concentrations (MIC50) and 90% inhibitory concentrations (MIC90) for multidrug-resistant strains of mucoid Pseudomonas aeruginosa (n=200 strains), nonmucoid P. aeruginosa (n=200), and Burkholderia cepacia complex (n=200) isolated from patients with cystic fibrosis were 8 and 32, 8 and 64, and 8 and 32 microg/ml, respectively. Doripenem had somewhat better activity than established antimicrobial agents.

A novel model to study bacterial adherence to the transplanted airway: inhibition of Burkholderia cepacia adherence to human airway by dextran and xylitol

BACKGROUND

Lung infection with Burkholderia cepacia complex before lung transplantation in patients with cystic fibrosis is a major risk factor for decreased post-operative survival rates compared with those of patients colonized with the more common opportunistic pathogen Pseudomonas aeruginosa. Because adherence to mucosal surfaces is an important initial step in infection, we investigated the use of non-toxic neutral polysaccharides and a sugar alcohol to prevent adherence of B cepacia complex to allograft airway epithelium.

METHODS

We used human airway explants prepared from donor tracheobronchial tissue to test the effect of dextrans and xylitol in inhibiting the binding of Burkholderia cepacia complex. We used immunofluorescence and electron microscopy to determine the distribution of bacteria in the explants.

RESULTS

Burkholderia cepacia complex bound to the explants and was found only in the surface mucus layer. Dextran 40 kd applied before adding the bacteria decreased the number of bound organisms by 80% to 99%. Smaller molecular mass dextrans (4 and 20 kd) were ineffective. Xylitol inhibited bacterial binding by 67% to 85%. Both agents seemed to decrease the thickness of the surface mucus, suggesting that they may indirectly inhibit bacterial binding by removing adherent surface mucus.

CONCLUSIONS

Treating donor lungs with dextran 40 kd or xylitol before (and possibly after) surgery may inhibit the adherence of Burkholderia cepacia complex to airways and may prevent or decrease subsequent infection of the allografts.

Use of breakpoint combination sensitivity testing as a simple and convenient method to evaluate the combined effects of ceftazidime and tobramycin on Pseudomonas aeruginosa and Burkholderia cepacia complex isolates in vitro

An in vitro method of determining the activity of antibiotics in combination which is simple and convenient to perform and which could be used routinely in clinical microbiology laboratories is desirable. We investigated the activity, against Pseudomonas aeruginosa and Burkholderia cepacia complex clinical isolates, of ceftazidime and tobramycin in combination using a broth macrodilution sensitivity method based on breakpoint minimum inhibitory concentrations and compared the results obtained using this method with those obtained using the microtitre checkerboard method. There was good agreement in interpretation of results between the two methods for both P. aeruginosa (90%) and B. cepacia complex isolates (70%) with tobramycin and for P. aeruginosa isolates (70%) with ceftazidime. As the breakpoint combination sensitivity testing method employs only four tubes and does not require initial determination of individual antibiotic minimum inhibitory concentrations, it is simpler and more convenient for determining the activity of antibiotics in combination than the microtitre checkerboard method. The use of this method in routine microbiology laboratories to determine the activity of antibiotic combinations against clinical isolates should optimise treatment of infection by ensuring that appropriate antibiotic combinations are prescribed.

Isolation of Burkholderia cepacia complex genomovars from waters

The aim of this study was to develop a selective enrichment broth as an aid for the isolation of Burkholderia cepacia complex (Bcc) bacteria from water. To allow growth of all nine genomovars, mixtures of two carbon sources had to be used, i.e. L-arabinose/D-cellobiose or L-arabinose/L-threonine. Selectivity was provided by polymyxin B and 9-chloro-9-(4-diethylaminophenyl)-10-phenylacridan (C-390). Following enrichment, Bcc bacteria were isolated on a diagnostic O/F agar supplemented with gentamicin. A preliminary bio-diversity study on 28 surface waters yielded five different genomovars, i.e. B. cepacia (genomovar I), B. multivorans, B. cenocepacia, B. vietnamiensis and B. anthina. Drinking waters did not contain Bcc bacteria. However, the genomovar pattern from a given sample varied with the enrichment broth used.