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

Phage therapy to treat cystic fibrosis Burkholderia cepacia complex lung infections: perspectives and challenges

Burkholderia cepacia complex is a cause of serious lung infections in people with cystic fibrosis, exhibiting extremely high levels of antimicrobial resistance. These infections are difficult to treat and are associated with high morbidity and mortality. With a notable lack of new antibiotic classes currently in development, exploring alternative antimicrobial strategies for Burkholderia cepacia complex is crucial. One potential alternative seeing renewed interest is the use of bacteriophage (phage) therapy. This review summarises what is currently known about Burkholderia cepacia complex in cystic fibrosis, as well as challenges and insights for using phages to treat Burkholderia cepacia complex lung infections.

Small-molecule activators of a bacterial signaling pathway inhibit virulence

The Burkholderia genus encompasses multiple human pathogens, including potential bioterrorism agents, that are often extensively antibiotic resistant. The FixLJ pathway in Burkholderia is a two-component system that regulates virulence. Previous work showed that fixLJ mutations arising during chronic infection confer increased virulence while decreasing the activity of the FixLJ pathway. We hypothesized that small-molecule activators of the FixLJ pathway could serve as anti-virulence therapies. Here, we developed a high-throughput assay that screened over 28,000 compounds and identified 11 that could specifically active the FixLJ pathway. Eight of these compounds, denoted Burkholderia Fix Activator (BFA) 1-8, inhibited the intracellular survival of Burkholderia in THP-1-dervived macrophages in a fixLJ-dependent manner without significant toxicity. One of the compounds, BFA1, inhibited the intracellular survival in macrophages of multiple Burkholderia species. Predictive modeling of the interaction of BFA1 with Burkholderia FixL suggests that BFA1 binds to the putative ATP/ADP binding pocket in the kinase domain, indicating a potential mechanism for pathway activation. These results indicate that small-molecule FixLJ pathway activators are promising anti-virulence agents for Burkholderia and define a new paradigm for antibacterial therapeutic discovery.

Examining the activity of cefepime-taniborbactam against Burkholderia cepacia complex and Burkholderia gladioli isolated from cystic fibrosis patients in the United States

The novel clinical-stage β-lactam-β-lactamase inhibitor combination, cefepime-taniborbactam, demonstrates promising activity toward many Gram-negative bacteria producing class A, B, C, and/or D β-lactamases. We tested this combination against a panel of 150 Burkholderia cepacia complex (Bcc) and Burkholderia gladioli strains. The addition of taniborbactam to cefepime shifted cefepime minimum inhibitory concentrations toward the provisionally susceptible range in 59% of the isolates tested. Therefore, cefepime-taniborbactam possessed similar activity as first-line agents, ceftazidime and trimethoprim-sulfamethoxazole, supporting further development.

Stenotrophomonas maltophilia in people with Cystic Fibrosis: a systematic review of prevalence, risk factors and management

To summarize the current knowledge of the clinical impact of Stenotrophomonas maltophilia (SM) in cystic fibrosis (CF) patients. A systematic review according to the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guideline recommendations, was performed through searches in PubMed and EMBASE databases, and CF National and International Registries websites from 2000 to 2022. Overall, 184 articles were initially retrieved, out of which 15 were selected and included in the review. Data form 6 Registries and 9 pertinent articles from the references of the studies selected were also considered, resulting in 30 studies in total. The prevalence of SM in patients with CF is increasing in Europe while it is declining in North America. The role of chronic colonization of SM on lung function and clinical status in CF patients is still under debate. The most recent studies suggested a pathogenic role of SM chronic infections in CF patients with an acceleration in lung function decline, an increase in hospitalization rates and an association with co-infection. Reflecting the uncertainty about the role of SM in CF, little is available about antibiotic therapeutic strategies for both acute exacerbations and chronic infections. Antimicrobial therapy should be performed in the acute exacerbations, while it may be reasonable to attempt eradication when the first colonization is identified. Nevertheless, it is not established which antibiotic regimen should be preferred, and overtreatment could contribute to the selection of antimicrobial-resistant strains. Further studies are warranted in this regard.

Comparative Genomics Identified PenR E151V Substitution Associated with Carbapenem-Resistance Burkholderia cepacia Complex and a Novel Burkholderia cepacia Complex Specific OXA-1043 Subgroup

Purpose

Burkholderia cepacia complex (Bcc) is a known significant opportunistic pathogen causing morbidity and mortality, particularly in those with cystic fibrosis, chronic granulomatous disease, or immunocompromising host. Mortality of Bcc bloodstream infections among non-cystic fibrosis patients remained high. The antibiotic treatment for Bcc infection is quite challenging due to its intrinsic resistance to most antibiotics, and the resistance to carbapenems was the biggest concern among them. We aimed to realize the mechanism of carbapenem resistance in Bcc.

Patients and Methods

Ten strains of Bcc were identified by the MALDI-TOF MS, and the drug susceptibility test was using VITEK 2 system. The Burkholderia cepacia complex genomes were sequenced via Nanopore GridIon. We also downloaded another ninety-five strains of Bcc from the National Center for Biotechnology Information database to evaluate the divergence between carbapenem-resistance and carbapenem-sensitive strains.

Results

The genetic organization between carbapenem-sensitive and carbapenem-resistant strains of Bcc showed no difference. However, in the carbapenem-sensitive strain, E151V substitution in PenR was detected. In addition, a novel specific OXA family subgroup, blaOXA-1043 in Burkholderia cenocepacia was discovered.

Conclusion

The E151V substitution in PenR may be associated with carbapenem-sensitive in Bcc. Moreover, the V151E mutation in PenR may be related to the activation of PenB, leading to Bcc resistance to carbapenems. Besides, a novel OXA family subgroup, blaOXA-1043, was found in Burkholderia cenocepacia, which differs from the previous OXA family.

Profiling cell envelope-antibiotic interactions reveals vulnerabilities to β-lactams in a multidrug-resistant bacterium

The cell envelope of Gram-negative bacteria belonging to the Burkholderia cepacia complex (Bcc) presents unique restrictions to antibiotic penetration. As a consequence, Bcc species are notorious for causing recalcitrant multidrug-resistant infections in immunocompromised individuals. Here, we present the results of a genome-wide screen for cell envelope-associated resistance and susceptibility determinants in a Burkholderia cenocepacia clinical isolate. For this purpose, we construct a high-density, randomly-barcoded transposon mutant library and expose it to 19 cell envelope-targeting antibiotics. By quantifying relative mutant fitness with BarSeq, followed by validation with CRISPR-interference, we profile over a hundred functional associations and identify mediators of antibiotic susceptibility in the Bcc cell envelope. We reveal connections between β-lactam susceptibility, peptidoglycan synthesis, and blockages in undecaprenyl phosphate metabolism. The synergy of the β-lactam/β-lactamase inhibitor combination ceftazidime/avibactam is primarily mediated by inhibition of the PenB carbapenemase. In comparison with ceftazidime, avibactam more strongly potentiates the activity of aztreonam and meropenem in a panel of Bcc clinical isolates. Finally, we characterize in Bcc the iron and receptor-dependent activity of the siderophore-cephalosporin antibiotic, cefiderocol. Our work has implications for antibiotic target prioritization, and for using additional combinations of β-lactam/β-lactamase inhibitors that can extend the utility of current antibacterial therapies.

Burkholderia contaminans Bacteriophage CSP3 Requires O-Antigen Polysaccharides for Infection

The Burkholderia cepacia complex is a group of opportunistic pathogens that cause both severe acute and chronic respiratory infections. Due to their large genomes containing multiple intrinsic and acquired antimicrobial resistance mechanisms, treatment is often difficult and prolonged. One alternative to traditional antibiotics for treatment of bacterial infections is bacteriophages. Therefore, the characterization of bacteriophages infective for the Burkholderia cepacia complex is critical to determine their suitability for any future use. Here, we describe the isolation and characterization of novel phage, CSP3, infective against a clinical isolate of Burkholderia contaminans. CSP3 is a new member of the Lessievirus genus that targets various Burkholderia cepacia complex organisms. Single nucleotide polymorphism (SNP) analysis of CSP3-resistant B. contaminans showed that mutations to the O-antigen ligase gene, waaL, consequently inhibited CSP3 infection. This mutant phenotype is predicted to result in the loss of cell surface O-antigen, contrary to a related phage that requires the inner core of the lipopolysaccharide for infection. Additionally, liquid infection assays showed that CSP3 provides suppression of B. contaminans growth for up to 14 h. Despite the inclusion of genes that are typical of the phage lysogenic life cycle, we saw no evidence of CSP3's ability to lysogenize. Continuation of phage isolation and characterization is crucial in developing large and diverse phage banks for global usage in cases of antibiotic-resistant bacterial infections. IMPORTANCE Amid the global antibiotic resistance crisis, novel antimicrobials are needed to treat problematic bacterial infections, including those from the Burkholderia cepacia complex. One such alternative is the use of bacteriophages; however, a lot is still unknown about their biology. Bacteriophage characterization studies are of high importance for building phage banks, as future work in developing treatments such as phage cocktails should require well-characterized phages. Here, we report the isolation and characterization of a novel Burkholderia contaminans phage that requires the O-antigen for infection, a distinct phenotype seen among other related phages. Our findings presented in this article expand on the ever-evolving phage biology field, uncovering unique phage-host relationships and mechanisms of infection.

Synergistic Interactions among Burkholderia cepacia Complex-Targeting Phages Reveal a Novel Therapeutic Role for Lysogenization-Capable Phages

Antimicrobial resistance is a danger to global public health and threatens many aspects of modern medicine. Bacterial species such as those of the Burkholderia cepacia complex (Bcc) cause life-threatening respiratory infections and are highly resistant to antibiotics. One promising alternative being explored to combat Bcc infections is phage therapy (PT): the use of phages to treat bacterial infections. Unfortunately, the utility of PT against many pathogenic species is limited by its prevailing paradigm: that only obligately lytic phages should be used therapeutically. It is thought that 'lysogenic' phages do not lyse all bacteria and can transfer antimicrobial resistance or virulence factors to their hosts. We argue that the tendency of a lysogenization-capable (LC) phage to form stable lysogens is not predicated exclusively on its ability to do so, and that the therapeutic suitability of a phage must be evaluated on a case-by-case basis. Concordantly, we developed several novel metrics-Efficiency of Phage Activity, Growth Reduction Coefficient, and Stable Lysogenization Frequency-and used them to evaluate eight Bcc-specific phages. Although these parameters vary considerably among Bcc phages, a strong inverse correlation (R2 = 0.67; P < 0.0001) exists between lysogen formation and antibacterial activity, indicating that certain LC phages with low frequency of stable lysogenization may be therapeutically efficacious. Moreover, we show that many LC Bcc phages interact synergistically with other phages in the first reported instance of mathematically defined polyphage synergy, and that these interactions result in the eradication of in vitro bacterial growth. Together, these findings reveal a novel therapeutic role for LC phages and challenge the current paradigm of PT. IMPORTANCE The spread of antimicrobial resistance is an imminent threat to public health around the world. Particularly concerning are species of the Burkholderia cepacia complex (Bcc), which cause life-threatening respiratory infections and are notoriously resistant to antibiotics. Phage therapy is a promising alternative being explored to combat Bcc infections and antimicrobial resistance in general, but its utility against many pathogenic species, including the Bcc, is restricted by the currently prevailing paradigm of exclusively using rare obligately lytic phages due to the perception that 'lysogenic' phages are therapeutically unsuitable. Our findings show that many lysogenization-capable phages exhibit powerful in vitro antibacterial activity both alone and through mathematically defined synergistic interactions with other phages, demonstrating a novel therapeutic role for LC phages and therefore challenging the currently prevailing paradigm of PT.

Activity of ETX0462 toward Some Burkholderia spp

Burkholderia cepacia complex (Bcc) and Burkholderia gladioli are opportunistic human pathogens that are inherently multidrug resistant, limiting treatment options for infections. Here, a novel diazabicyclooctane, ETX0462, was evaluated for activity against Bcc and B. gladioli. Ninety-eight percent of the isolates examined in this study were susceptible. ETX0462 was found to demonstrate in vitro activity superior to that of currently available treatment options (e.g., trimethoprim-sulfamethoxazole and ceftazidime).

The Status of Carbapenem Resistance in Cystic Fibrosis: A Systematic Review and Meta-Analysis

Background: Antibiotic resistance in cystic fibrosis (CF) is a well-known phenomenon. However, the comprehensive epidemiological impact of antibiotic resistance in CF is not clearly documented. So, this meta-analysis evaluated the proportion rates of carbapenem resistance (imipenem, meropenem, and doripenem) in CF based on publication date (1979-2000, 2001-2010, and 2011-2021), continents, pathogens, and antimicrobial susceptibility testing (AST). Methods: We searched studies in PubMed, Scopus, and Web of Science (until April 2021). Statistical analyses were conducted using STATA software (version 14.0). Results: The 110 studies included in the analysis were performed in 25 countries and investigated 13,324 pathogens associated with CF. The overall proportion of imipenem, meropenem, and doripenem resistance in CF were 43% (95% CI 36-49), 48% (95% CI 40-57), 28% (95% CI 23-33), and 45% (95% CI 32-59), respectively. Our meta-analysis showed that trends of imipenem, meropenem, and doripenem-resistance had gradual decreases over time (1979-2021). This could be due to the limited clinical effectiveness of these antibiotics to treat CF cases over time. Among the opportunistic pathogens associated with CF, the highest carbapenem resistance rates were shown in Stenotrophomonas maltophilia, Burkholderia spp., Pseudomonas aeruginosa, and Staphylococcus aureus. The highest and lowest carbapenem resistance rates among P. aeruginosa in CF patients were shown against meropenem (23%) and doripenem (39%). Conclusions: We showed that trends of carbapenem resistance had decreased over time (1979-2021). This could be due to the limited clinical effectiveness of these antibiotics to treat CF cases over time. Plans should be directed to fight biofilm-associated infections and prevent the emergence of mutational resistance. Systematic surveillance for carbapenemase-producing pathogens in CF by molecular surveillance is necessitated.

Protein with negative surface charge distribution, Bnr1, shows characteristics of a DNA-mimic protein and may be involved in the adaptation of Burkholderia cenocepacia

Adaptation of opportunistic pathogens to their host environment requires reprogramming of a vast array of genes to facilitate survival in the host. Burkholderia cenocepacia, a Gram-negative bacterium with a large genome of ∼8 Mb that colonizes environmental niches, is exquisitely adaptable to the hypoxic environment of the cystic fibrosis lung and survives in macrophages. We previously identified an immunoreactive acidic protein encoded on replicon 3, BCAS0292. Deletion of the BCAS0292 gene significantly altered the abundance of 979 proteins by 1.5-fold or more; 19 proteins became undetectable while 545 proteins showed ≥1.5-fold reduced abundance, suggesting the BCAS0292 protein is a global regulator. Moreover, the ∆BCAS0292 mutant showed a range of pleiotropic effects: virulence and host-cell attachment were reduced, antibiotic susceptibility was altered, and biofilm formation enhanced. Its growth and survival were impaired in 6% oxygen. In silico prediction of its three-dimensional structure revealed BCAS0292 presents a dimeric β-structure with a negative surface charge. The ΔBCAS0292 mutant displayed altered DNA supercoiling, implicated in global regulation of gene expression. Three proteins were identified in pull-downs with FLAG-tagged BCAS0292, including the Histone H1-like protein, HctB, which is recognized as a global transcriptional regulator. We propose that BCAS0292 protein, which we have named Burkholderia negatively surface-charged regulatory protein 1 (Bnr1), acts as a DNA-mimic and binds to DNA-binding proteins, altering DNA topology and regulating the expression of multiple genes, thereby enabling the adaptation of B. cenocepacia to highly diverse environments.

Diabetic foot infection caused by bacteria of the Burkholderia cepacia complex: report of an unusual case and a scoping literature review

Burkholderia cepacia complex (BCC) is group of widespread gram-negative bacillus organized in over 20 phylogenetically distinct bacterial species. According to previous studies, BCC species pathogens are widely reported in patients with cystic fibrosis (CF), but not in individuals with diabetes mellitus (DM). In this case report, a 42-year-old male patient with DM and a foot infection caused by BCC is presented. The patient was hospitalized after antibiotic treatment failure and improved after two surgical debridement procedures and a high-dose extended infusion (EI) of meropenem. The team of vascular surgeons and the infectious disease specialists worked fervently to solve the case. Finally, a scoping review was conducted to map BCC infections in patients with DM.

Evaluation of Antimicrobial Susceptibility Testing Methods for Burkholderia cenocepacia and Burkholderia multivorans Isolates from Cystic Fibrosis Patients

The Burkholderia cepacia complex (BCC) is known for causing serious lung infections in people with cystic fibrosis (CF). These infections can require lung transplantation, eligibility for which may be guided by antimicrobial susceptibility testing (AST). While the Clinical and Laboratory Standards Institute recommends AST for BCC, the European Committee on Antimicrobial Susceptibility Testing (EUCAST) does not, due to poor method performance and correlation with clinical outcomes. Furthermore, limited data exist on the performance of automated AST methods for BCC. To address these issues, reproducibility and accuracy were evaluated for disk diffusion (DD), broth microdilution (BMD), and MicroScan WalkAway using 50 B. cenocepacia and 50 B. multivorans isolates collected from people with CF. The following drugs were evaluated in triplicate: chloramphenicol (CAM), ceftazidime (CAZ), meropenem (MEM), trimethoprim-sulfamethoxazole (TMP-SMX), minocycline (MIN), levofloxacin (LVX), ciprofloxacin (CIP), and piperacillin-tazobactam (PIP-TAZ). BMD reproducibility was ≥ 95% for MEM and MIN only, and MicroScan WalkAway reproducibility was similar to BMD. DD reproducibility was < 90% for all drugs tested when a 3 mm cut-off was applied. When comparing the accuracy of DD to BMD, only MEM met all acceptance criteria. TMP-SMX and LVX had high minor errors, CAZ had unacceptable very major errors (VME), and MIN, PIP-TAZ, and CIP had both unacceptable minor errors and VMEs. For MicroScan WalkAway, no drugs met acceptance criteria. Analyses also showed that errors were not attributed to one species. In general, our data agree with EUCAST recommendations.

Outer membrane vesicles produced by Burkholderia cepacia cultured with subinhibitory concentrations of ceftazidime enhance pro-inflammatory responses

BURKHOLDERIA CEPACIA

is an opportunistic pathogen that infects patients with debilitating underlying diseases. This study investigated the production of outer membrane vesicles (OMVs) by B. cepacia cultured with sub-minimum inhibitory concentrations (MICs) of antibiotics and examined their pathogenic roles both in vitro and in vivo. B. cepacia ATCC 25416 produced more OMVs under antibiotic stress conditions than controls. OMVs isolated from B. cepacia cultured in Luria-Bertani (LB) broth (OMVs/LB) induced cytotoxicity and the expression of pro-inflammatory cytokine genes in A549 cells in a dose-dependent manner. Host cell cytotoxicity and pro-inflammatory responses were significantly higher in A549 cells treated with B. cepacia OMVs cultured with 1/4 MIC of ceftazidime (OMVs/CAZ) than in the cells treated with OMVs/LB, OMVs cultured with 1/4 MIC of trimethoprim/sulfamethoxazole (OMVs/SXT), or OMVs cultured with 1/4 MIC of meropenem. Intratracheal injection of B. cepacia OMVs also induced histopathology in vivo in mouse lungs. Expressions of IL-1β and TNF-α genes were significantly up-regulatedin the lungs of mice treated with OMVs/CAZ compared to mice administered other OMVs; the expression of the GRO-α gene, however, was significantly up-regulated in OMVs/SXT. In conclusion, OMVs produced by B. cepacia under different antibiotic stress conditions induce different host responses that may contribute to the pathogenesis of B. cepacia.

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.

Evaluation of susceptibility testing methods for Burkholderia cepacia complex: a comparison of broth microdilution, agar dilution, gradient strip and EUCAST disc diffusion

OBJECTIVES

To evaluate the accuracy and reproducibility of antimicrobial susceptibility testing methods in Burkholderia cepacia complex (BCC).

METHODS

Minocycline, ciprofloxacin, trimethoprim/sulphamethoxazole, meropenem, ceftazidime and chloramphenicol were tested against 155 BCC strains using broth microdilution at 35 ± 1°C (BMD35) in triplicate, then BMD at 30 ± 1°C (BMD30), agar dilution at 30°C and 35°C (AD30 and AD35), gradient strip (GS) and EUCAST standardized disc diffusion (DD) testing methods once.

RESULTS

BMD35 reproducibility ranged from 70% to 84.5% for all agents. Correlations of MICs from BMD35 with BMD30 ranged from 63% to 85%, with AD35 from 32.9% to 87% and with GS methods from 36% to 83.9%. Essential agreement (EA) of MICs by GS with BMD35 ranged from 62.6% (trimethoprim-sulphamethoxazole) to 83.9% (minocycline). EA of EUCAST DD zone diameters using CLSI breakpoint criteria was between 85.8% and 97.4%, however Very Major Errors (VME) for trimethoprim/sulphamethoxazole were 31%.

CONCLUSIONS

BMD at 35 ± 1°C was poorly reproducible for most agents and no method showed acceptable performance. Of particular concern were the GS results. Although this is the most commonly used method for determining MICs in laboratories, there was poor correlation with BMD35 for meropenem and trimethoprim/sulphamethoxazole. EUCAST DD correlated poorly with BMD35 MICs. This study confirms that no susceptibility method is capable of providing reproducible and accurate MICs when testing BCC.

A rapid screening method for the detection of specialised metabolites from bacteria: Induction and suppression of metabolites from Burkholderia species

Screening microbial cultures for specialised metabolites is essential for the discovery of new biologically active compounds. A novel, cost-effective and rapid screening method is described for extracting specialised metabolites from bacteria grown on agar plates, coupled with HPLC for basic identification of known and potentially novel metabolites. The method allows the screening of culture collections to identify optimal production strains and metabolite induction conditions. The protocol was optimised on two Burkholderia species known to produce the antibiotics, enacyloxin IIa (B. ambifaria) and gladiolin (B. gladioli), respectively; it was then applied to strains of each species to identify high antibiotic producers. B. ambifaria AMMD and B. gladioli BCC0238 produced the highest concentrations of the respective antibiotic under the conditions tested. To induce expression of silent biosynthetic gene clusters, the addition of low concentrations of antibiotics to growth media was evaluated as known elicitors of Burkholderia specialised metabolites. Subinhibitory concentrations of trimethoprim and other clinically therapeutic antibiotics were evaluated and screened against a panel of B. gladioli and B. ambifaria. To enhance rapid strain screening with more antibiotic elicitors, antimicrobial susceptibility testing discs were included within the induction medium. Low concentrations of trimethoprim suppressed the production of specialised metabolites in B. gladioli, including the toxins, toxoflavin and bongkrekic acid. However, the addition of trimethoprim significantly improved enacylocin IIa concentrations in B. ambifaria AMMD. Rifampicin and ceftazidime significantly improved the yield of gladiolin and caryoynencin by B. gladioli BCC0238, respectively, and cepacin increased 2-fold with tobramycin in B. ambifaria BCC0191. Potentially novel metabolites were also induced by subinhibitory concentrations of tobramycin and chloramphenicol in B. ambifaria. In contrast to previous findings that low concentrations of antibiotic elicit Burkholderia metabolite production, we found they acted as both inducers or suppressors dependent on the metabolite and the strains producing them. In conclusion, the screening protocol enabled rapid characterization of Burkholderia metabolites, the identification of suitable producer strains, potentially novel natural products and an understanding of metabolite regulation in the presence of inducing or suppressing conditions.

Revisiting aminocoumarins for the treatment of melioidosis

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Aminocoumarins can be used to treat acute pulmonary melioidosis in a murine model.

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Formulation with l-tyrosine or dl-tryptophan enhances the bioactivity of aminocoumarins.

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Utility of Galleria mellonella larvae for in vivo drug efficacy screening.

Burkholderia pseudomallei causes melioidosis, a potentially lethal disease that can establish both chronic and acute infections in humans. It is inherently recalcitrant to many antibiotics, there is a paucity of effective treatment options and there is no vaccine. In the present study, the efficacies of selected aminocoumarin compounds, DNA gyrase inhibitors that were discovered in the 1950s but are not in clinical use for the treatment of melioidosis were investigated. Clorobiocin and coumermycin were shown to be particularly effective in treating B. pseudomallei infection in vivo. A novel formulation with dl-tryptophan or l-tyrosine was shown to further enhance aminocoumarin potency in vivo. It was demonstrated that coumermycin has superior pharmacokinetic properties compared with novobiocin, and the coumermycin in l-tyrosine formulation can be used as an effective treatment for acute respiratory melioidosis in a murine model. Repurposing of existing approved antibiotics offers new resources in a challenging era of drug development and antimicrobial resistance.

Exploring the Interplay of Resistance Nodulation Division Efflux Pumps, AmpC and OprD in Antimicrobial Resistance of Burkholderia cepacia Complex in Clinical Isolates

Aim: This study aimed at investigating the association of gene expression of multidrug efflux pumps (MexA, MexC, MexE, and MexX), the outer membrane porin OprD, and the β-lactamase AmpC with the antimicrobial susceptibility among 44 clinical isolates of Burkholderia cepacia complex (Bcc). Results: Increased expression of ampC gene showed significant association with reduced susceptibility to chloramphenicol. In fact, reduced susceptibility to chloramphenicol was correlated with overexpression of most genes (ampC, mexC, mexE, and mexX) studied here in majority (>95%) of the Bcc isolates. Increased mexA expression showed significant association with reduced susceptibility to β-lactam antimicrobials (ceftazidime, piperacillin-tazobactam, and meropenem) and co-trimoxazole. Reduced susceptibility to meropenem also showed significant correlation with overexpression of mexC and mexX, whereas reduced susceptibility to ceftazidime was also associated with mexE overexpression. Reduced susceptibility to levofloxacin was significantly associated with overexpression of mexX. The involvement of the efflux pumps in levofloxacin and ceftazidime resistance was further inferred from the finding that the efflux pump inhibitor, carbonyl cyanide m-chlorophenylhydrazone reduced minimum inhibitory concentrations for both the antimicrobials. Conclusions: To conclude, this study explored the high-level expression of mexC, mexE, and mexX efflux pumps genes and ampC in the clinical isolates of Bcc, which can be targeted at treating infections caused by Bcc.

Endolysins as emerging alternative therapeutic agents to counter drug-resistant infections

Endolysins are the lytic products of bacteriophages which play a specific role in the release of phage progeny by degrading the peptidoglycan of the host bacterium. In the light of antibiotic resistance, endolysins are being considered as alternative therapeutic agents because of their exceptional ability to target bacterial cells when applied externally. Endolysins have been studied against a number of drug-resistant pathogens to assess their therapeutic ability. This review focuses on the structure of endolysins in terms of cell binding and catalytic domains, lytic ability, resistance, safety, immunogenicity and future applications. It primarily reviews recent advancements made in evaluation of the therapeutic potential of endolysins, including their origin, host range, applications, and synergy with conventional and non-conventional antimicrobial agents.

The Effect of 2-Thiocyanatopyridine Derivative 11026103 on Burkholderia Cenocepacia: Resistance Mechanisms and Systemic Impact

Bacteria of the Burkholderia cepacia complex (Bcc) are associated with significant decline of lung functions in cystic fibrosis patients. Bcc infections are virtually impossible to eradicate due to their irresponsiveness to antibiotics. The 2-thiocyanatopyridine derivative 11026103 is a novel, synthetic compound active against Burkholderia cenocepacia. To characterize mechanisms of resistance to 11026103, B. cenocepacia was subjected to chemical mutagenesis, followed by whole genome sequencing. Parallel mutations in resistant isolates were localized in a regulatory protein of the efflux system Resistance-Nodulation-Division (RND)-9 (BCAM1948), RNA polymerase sigma factor (BCAL2462) and its cognate putative anti-sigma factor (BCAL2461). Transcriptomic analysis identified positive regulation of a major facilitator superfamily (MFS) efflux system BCAL1510-1512 by BCAL2462. Artificial overexpression of both efflux systems increased resistance to the compound. The effect of 11026103 on B. cenocepacia was analyzed by RNA-Seq and a competitive fitness assay utilizing an essential gene knockdown mutant library. 11026103 exerted a pleiotropic effect on transcription including profound downregulation of cluster of orthologous groups (COG) category “Translation, ribosomal structure, and biogenesis”. The competitive fitness assay identified many genes which modulated susceptibility to 11026103. In summary, 11026103 exerts a pleiotropic cellular response in B. cenocepacia which can be prevented by efflux system-mediated export.

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.

Common Infections Following Lung Transplantation

The lungs are the only transplanted organ in direct contact with the ‘outside world’. Infection is a significant cause of morbidity and mortality in lung transplantation. Early accurate diagnosis and optimal management is essential to prevent short and long term complications. Bacteria, including Mycobacteria and Nocardia, viruses and fungi are common pathogens. Organisms may be present in the recipient prior to transplantation, transmitted with the donor lungs or acquired after transplantation. The degree of immunosuppression and the routine use of antimicrobial prophylaxis alters the pattern of post-transplant infections.

Successful Lung Re-transplant in a Patient with Cepacia Syndrome due to Burkholderia ambifaria

Chronic airway inflammation and infection drive morbidity and mortality among patients with cystic fibrosis (CF). While Haemophilus influenzae and Staphylococcus aureus predominate in children, the prevalence of Pseudomonas aeruginosa increases as patients age. Other bacteria, including species within the Burkholderia cepacia complex (Bcc), are also more prevalent among adults with CF. Species within the Bcc accelerate lung function decline and can trigger development of "cepacia syndrome," both before and after lung transplantation. As a result, some centers advise against lung transplantation for Bcc-infected patients; however, little is known about the relative virulence of uncommon Bcc species. We describe a successful lung re-transplant in a patient with CF, chronic Burkholderia ambifaria airway infection, and cepacia syndrome.

In Vitro Susceptibility of Burkholderia cepacia Complex Isolated from Cystic Fibrosis Patients to Ceftazidime-Avibactam and Ceftolozane-Tazobactam

We tested the in vitro susceptibility of ceftazidime-avibactam and ceftolozane-tazobactam and 13 other antibiotics against 91 Burkholderia cepacia complex (BCC) strains isolated from cystic fibrosis patients since 2012. The highest susceptibility (82%) was found for trimethoprim-sulfamethoxazole. Eighty-one and 63% of all BCC strains were susceptible to ceftazidime-avibactam and ceftolozane-tazobactam, respectively. For temocillin, ceftazidime, piperacillin-tazobactam, and meropenem, at least 50% of the strains were susceptible. B. stabilis seems to be more resistant than other BCC species.

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.

Antibacterial effects of microbial synthesized silver-copper nanoalloys on Escherichia coli, Burkholderia cepacia, Listeria monocytogenes and Brucella abortus

BACKGROUND AND OBJECTIVES

Bacterial resistance is an emerging public health problem worldwide. Metallic nanoparticles and nanoalloys open a promising field due to their excellent antimicrobial effects. The aim of the present study was to investigate the antibacterial effects of Ag-Cu nanoalloys, which were biosynthesized by Lactobacillus casei ATCC 39392, on some of the important bacterial pathogens, including Escherichia coli, Burkholderia cepacia, Listeria monocytogenes and Brucella abortus.

MATERIALS AND METHODS

Ag-Cu nanoalloys were synthesized through the microbial reduction of AgNO3 and CuSO4 by Lactobacillus casei ATCC39392. Furthermore, they were characterized by Fourier-Transform Infrared Spectrometer (FTIR) and Field Emission Scanning Electron Microscopy (FESEM) analysis in order to investigate their chemical composition and morphological features, respectively. The minimum inhibitory and minimum bactericidal concentrations of Ag-Cu nanoalloys were determined against each strain. The bactericidal test was conducted on the surface of MHA supplemented with 1, 0.1, and 0.01 μg/μL of the synthesized nanoalloy. The antimicrobial effects of synthesized nanoalloy were compared with ciprofloxacin, ampicillin and ceftazidime as positive controls.

RESULTS

Presence of different chemical functional groups, including N-H, C-H, C-N and C-O on the surface of Ag-Cu nanoalloys was recorded by FTIR. FESEM micrographs revealed uniformly distributed nanoparticles with spherical shape and size ranging from 50 to 100 nm. The synthesized Ag-Cu nanoalloys showed antibacterial activity against L. monocytogenes PTCC 1298, E. coli ATCC 25922 and B. abortus vaccine strain. However, no antibacterial effects were observed against B. cepacia ATCC 25416.

CONCLUSION

According to the findings of the present research, the microbially synthesized Ag-Cu nanoalloy demonstrated antibacterial effects on the majority of the bacteria studied even at 0.01 μg/μL. However, complementary investigations should be conducted into the safety of this nanoalloy for in vivo or systemic use.

Successful Treatment of Persistent Burkholderia cepacia Complex Bacteremia with Ceftazidime-Avibactam

We report our clinical experience treating a 2-month-old infant with congenital diaphragmatic hernia who experienced prolonged bacteremia with Burkholderia cepacia complex (Bcc) despite conventional antibiotic therapy and appropriate source control measures. The infection resolved after initiation of ceftazidime-avibactam. Whole-genome sequencing revealed that the isolate most closely resembled B. contaminans and identified the mechanism of resistance that likely contributed to clinical cure with this agent. Ceftazidime-avibactam should be considered salvage therapy for Bcc infections if other treatment options have been exhausted.

Novel antibiotic combinations proposed for treatment of Burkholderia cepacia complex infections

Effective strategies to manage Burkholderia cepacia complex (Bcc) infections in cystic fibrosis (CF) patients are lacking. We tested combinations of clinically available antibiotics and show that moxifloxacin-ceftazidime could inhibit 16 Bcc clinical isolates at physiologically achievable concentrations. Adding low dose of colistin improved the efficacy of the combo, especially at conditions mimicking CF respiratory secretions.

Phylogeographic, genomic, and meropenem susceptibility analysis of Burkholderia ubonensis

The bacterium Burkholderia ubonensis is commonly co-isolated from environmental specimens harbouring the melioidosis pathogen, Burkholderia pseudomallei. B. ubonensis has been reported in northern Australia and Thailand but not North America, suggesting similar geographic distribution to B. pseudomallei. Unlike most other Burkholderia cepacia complex (Bcc) species, B. ubonensis is considered non-pathogenic, although its virulence potential has not been tested. Antibiotic resistance in B. ubonensis, particularly towards drugs used to treat the most severe B. pseudomallei infections, has also been poorly characterised. This study examined the population biology of B. ubonensis, and includes the first reported isolates from the Caribbean. Phylogenomic analysis of 264 B. ubonensis genomes identified distinct clades that corresponded with geographic origin, similar to B. pseudomallei. A small proportion (4%) of strains lacked the 920kb chromosome III replicon, with discordance of presence/absence amongst genetically highly related strains, demonstrating that the third chromosome of B. ubonensis, like other Bcc species, probably encodes for a nonessential pC3 megaplasmid. Multilocus sequence typing using the B. pseudomallei scheme revealed that one-third of strains lack the "housekeeping" narK locus. In comparison, all strains could be genotyped using the Bcc scheme. Several strains possessed high-level meropenem resistance (≥32 μg/mL), a concern due to potential transmission of this phenotype to B. pseudomallei. In silico analysis uncovered a high degree of heterogeneity among the lipopolysaccharide O-antigen cluster loci, with at least 35 different variants identified. Finally, we show that Asian B. ubonensis isolate RF23-BP41 is avirulent in the BALB/c mouse model via a subcutaneous route of infection. Our results provide several new insights into the biology of this understudied species.

Novel glycopolymer sensitizes Burkholderia cepacia complex isolates from cystic fibrosis patients to tobramycin and meropenem

Burkholderia cepacia complex (Bcc) infection, associated with cystic fibrosis (CF) is intrinsically multidrug resistant to antibiotic treatment making eradication from the CF lung virtually impossible. Infection with Bcc leads to a rapid decline in lung function and is often a contraindication for lung transplant, significantly influencing morbidity and mortality associated with CF disease. Standard treatment frequently involves antibiotic combination therapy. However, no formal strategy has been adopted in clinical practice to guide successful eradication. A new class of direct-acting, large molecule polycationic glycopolymers, derivatives of a natural polysaccharide poly-N-acetyl-glucosamine (PAAG), are in development as an alternative to traditional antibiotic strategies. During treatment, PAAG rapidly targets the anionic structural composition of bacterial outer membranes. PAAG was observed to permeabilize bacterial membranes upon contact to facilitate potentiation of antibiotic activity. Three-dimensional checkerboard synergy analyses were used to test the susceptibility of eight Bcc strains (seven CF clinical isolates) to antibiotic combinations with PAAG or ceftazidime. Potentiation of tobramycin and meropenem activity was observed in combination with 8-128 μg/mL PAAG. Treatment with PAAG reduced the minimum inhibitory concentration (MIC) of tobramycin and meropenem below their clinical sensitivity breakpoints (≤4 μg/mL), demonstrating the ability of PAAG to sensitize antibiotic resistant Bcc clinical isolates. Fractional inhibitory concentration (FIC) calculations showed PAAG was able to significantly potentiate antibacterial synergy with these antibiotics toward all Bcc species tested. These preliminary studies suggest PAAG facilitates a broad synergistic activity that may result in more positive therapeutic outcomes and supports further development of safe, polycationic glycopolymers for inhaled combination antibiotic therapy, particularly for CF-associated Bcc infections.

Molecular Simulations of Carbohydrates with a Fucose-Binding Burkholderia ambifaria Lectin Suggest Modulation by Surface Residues Outside the Fucose-Binding Pocket

Burkholderia ambifaria is an opportunistic respiratory pathogen belonging to the Burkholderia cepacia complex, a collection of species responsible for the rapidly fatal cepacia syndrome in cystic fibrosis patients. A fucose-binding lectin identified in the B. ambifaria genome, BambL, is able to adhere to lung tissue, and may play a role in respiratory infection. X-ray crystallography has revealed the bound complex structures for four fucosylated human blood group epitopes (blood group B, H type 1, H type 2, and Le^x determinants). The present study employed computational approaches, including docking and molecular dynamics (MD), to extend the structural analysis of BambL-oligosaccharide complexes to include four additional blood group saccharides (A, Le^a, Le^b, and Le^y) and a library of blood-group-related carbohydrates. Carbohydrate recognition is dominated by interactions with fucose via a hydrogen-bonding network involving Arg15, Glu26, Ala38, and Trp79 and a stacking interaction with Trp74. Additional hydrogen bonds to non-fucose residues are formed with Asp30, Tyr35, Thr36, and Trp74. BambL recognition is dominated by interactions with fucose, but also features interactions with other parts of the ligands that may modulate specificity or affinity. The detailed computational characterization of the BambL carbohydrate-binding site provides guidelines for the future design of lectin inhibitors.

Reclassification of the Specialized Metabolite Producer Pseudomonas mesoacidophila ATCC 31433 as a Member of the Burkholderia cepacia Complex

Pseudomonas mesoacidophila ATCC 31433 is a Gram-negative bacterium, first isolated from Japanese soil samples, that produces the monobactam isosulfazecin and the β-lactam-potentiating bulgecins. To characterize the biosynthetic potential of P. mesoacidophila ATCC 31433, its complete genome was determined using single-molecule real-time DNA sequence analysis. The 7.8-Mb genome comprised four replicons, three chromosomal (each encoding rRNA) and one plasmid. Phylogenetic analysis demonstrated that P. mesoacidophila ATCC 31433 was misclassified at the time of its deposition and is a member of the Burkholderia cepacia complex, most closely related to Burkholderia ubonensis The sequenced genome shows considerable additional biosynthetic potential; known gene clusters for malleilactone, ornibactin, isosulfazecin, alkylhydroxyquinoline, and pyrrolnitrin biosynthesis and several uncharacterized biosynthetic gene clusters for polyketides, nonribosomal peptides, and other metabolites were identified. Furthermore, P. mesoacidophila ATCC 31433 harbors many genes associated with environmental resilience and antibiotic resistance and was resistant to a range of antibiotics and metal ions. In summary, this bioactive strain should be designated B. cepacia complex strain ATCC 31433, pending further detailed taxonomic characterization.IMPORTANCE This work reports the complete genome sequence of Pseudomonas mesoacidophila ATCC 31433, a known producer of bioactive compounds. Large numbers of both known and novel biosynthetic gene clusters were identified, indicating that P. mesoacidophila ATCC 31433 is an untapped resource for discovery of novel bioactive compounds. Phylogenetic analysis demonstrated that P. mesoacidophila ATCC 31433 is in fact a member of the Burkholderia cepacia complex, most closely related to the species Burkholderia ubonensis Further investigation of the classification and biosynthetic potential of P. mesoacidophila ATCC 31433 is warranted.

Immune Recognition of the Epidemic Cystic Fibrosis Pathogen Burkholderia dolosa

Burkholderia dolosa caused an outbreak in the cystic fibrosis (CF) clinic at Boston Children's Hospital from 1998 to 2005 and led to the infection of over 40 patients, many of whom died due to complications from infection by this organism. To assess whether B. dolosa significantly contributes to disease or is recognized by the host immune response, mice were infected with a sequenced outbreak B. dolosa strain, AU0158, and responses were compared to those to the well-studied CF pathogen Pseudomonas aeruginosa In parallel, mice were also infected with a polar flagellin mutant of B. dolosa to examine the role of flagella in B. dolosa lung colonization. The results showed a higher persistence in the host by B. dolosa strains, and yet, neutrophil recruitment and cytokine production were lower than those with P. aeruginosa The ability of host immune cells to recognize B. dolosa was then assessed, B. dolosa induced a robust cytokine response in cultured cells, and this effect was dependent on the flagella only when bacteria were dead. Together, these results suggest that B. dolosa can be recognized by host cells in vitro but may avoid or suppress the host immune response in vivo through unknown mechanisms. B. dolosa was then compared to other Burkholderia species and found to induce similar levels of cytokine production despite being internalized by macrophages more than Burkholderia cenocepacia strains. These data suggest that B. dolosa AU0158 may act differently with host cells and is recognized differently by immune systems than are other Burkholderia strains or species.

Community-acquired urinary tract infections caused by Burkholderiacepacia complex in patients with no underlying risk factor

Introduction. Urinary tract infections (UTIs) remain common infections diagnosed in outpatients as well as hospitalized patients. Community-acquired UTIs are generally caused by Escherichia coli and other members of the family Enterobacteriaceae.Burkholderiacepacia is an opportunistic pathogen mainly affecting immunocompromised and hospitalized patients, particularly those who have received prior broad-spectrum antibacterial therapy.

Case presentation. Urine samples were collected from 157 outpatients clinically diagnosed with UTI and from 100 healthy control subjects. Samples were cultured on differential media and non-motile lactose-non-fermentors were identified via the Remel RapID ONE system. The isolates were tested by the disc diffusion method against 17 antimicrobial agents. Burkholderia was isolated as a single organism from four patients having uncomplicated infections, and one from recurrent infection. None of these patients had an underlying risk factor for this pathogen. Identification of these isolates by the Remel-RapID ONE system was confirmed by recA gene amplification. The four isolates were resistant to lincomycin, nalidixic acid, oxacillin and penicillin G. These cases received monotherapy of oral co-trimoxazole.

Conclusions. Our findings alert urologists and diagnostic laboratories to the potential of B.cepacia complex infections in similar cases, and that this bacterium should not be ruled out.

Competitive Growth Enhances Conditional Growth Mutant Sensitivity to Antibiotics and Exposes a Two-Component System as an Emerging Antibacterial Target in Burkholderia cenocepacia

Chemogenetic approaches to profile an antibiotic mode of action are based on detecting differential sensitivities of engineered bacterial strains in which the antibacterial target (usually encoded by an essential gene) or an associated process is regulated. We previously developed an essential-gene knockdown mutant library in the multidrug-resistant Burkholderia cenocepacia by transposon delivery of a rhamnose-inducible promoter. In this work, we used Illumina sequencing of multiplex-PCR-amplified transposon junctions to track individual mutants during pooled growth in the presence of antibiotics. We found that competition from nontarget mutants magnified the hypersensitivity of a clone underexpressing gyrB to novobiocin by 8-fold compared with hypersensitivity measured during clonal growth. Additional profiling of various antibiotics against a pilot library representing most categories of essential genes revealed a two-component system with unknown function, which, upon depletion of the response regulator, sensitized B. cenocepacia to novobiocin, ciprofloxacin, tetracycline, chloramphenicol, kanamycin, meropenem, and carbonyl cyanide 3-chlorophenylhydrazone, but not to colistin, hydrogen peroxide, and dimethyl sulfoxide. We named the gene cluster esaSR for enhanced sensitivity to antibiotics sensor and response regulator. Mutational analysis and efflux activity assays revealed that while esaS is not essential and is involved in antibiotic-induced efflux, esaR is an essential gene and regulates efflux independently of antibiotic-mediated induction. Furthermore, microscopic analysis of cells stained with propidium iodide provided evidence that depletion of EsaR has a profound effect on the integrity of cell membranes. In summary, we unraveled a previously uncharacterized two-component system that can be targeted to reduce antibiotic resistance in B. cenocepacia.

Activity of Cysteamine against the Cystic Fibrosis Pathogen Burkholderia cepacia Complex

There are no wholly successful chemotherapeutic strategies against Burkholderia cepacia complex (BCC) colonization in cystic fibrosis (CF). We assessed the impact of cysteamine (Lynovex) in combination with standard-of-care CF antibiotics in vitro against BCC CF isolates by the concentration at which 100% of bacteria were killed (MIC₁₀₀) and checkerboard assays under CLSI standard conditions. Cysteamine facilitated the aminoglycoside-, fluoroquinolone- and folate pathway inhibitor-mediated killing of BCC organisms that were otherwise resistant or intermediately sensitive to these antibiotic classes. Slow-growing BCC strains are often recalcitrant to treatment and form biofilms. In assessing the impact of cysteamine on biofilms, we demonstrated inhibition of BCC biofilm formation at sub-MIC₁₀₀s of cysteamine.

Combination antimicrobial susceptibility testing of Burkholderia cepacia complex: significance of species

The Burkholderia cepacia complex (Bcc) is notorious for the life-threatening pulmonary infections it causes in patients with cystic fibrosis. The multidrug-resistant nature of Bcc and differing infective Bcc species make the design of appropriate treatment regimens challenging. Previous synergy studies have failed to take account of the species of Bcc isolates. Etest methodology was used to facilitate minimum inhibitory concentration (MIC) and antimicrobial combination testing on 258 isolates of Bcc, identified to species level by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF/MS). The most active antimicrobials were trimethoprim/sulphamethoxazole, doxycycline and minocycline (52.5%, 46.4% and 45.9% of isolates susceptible, respectively). Synergy was observed in 9.2% of the 1799 combinations tested; the most common synergistic combinations were tobramycin + ceftazidime, meropenem + tobramycin and levofloxacin + piperacillin/tazobactam (35.4%, 32.3% and 22.2% synergy, respectively). Antimicrobial susceptibility analysis revealed differences between Burkholderia cenocepacia and Burkholderia multivorans. Disparity in clinical outcome during infection with these two micro-organisms necessitates further investigation into the clinical outcomes of treatment regimens in light of species identification and in vitro antimicrobial susceptibility studies.

Antibiotic resistance in Burkholderia species

The genus Burkholderia comprises metabolically diverse and adaptable Gram-negative bacteria, which thrive in often adversarial environments. A few members of the genus are prominent opportunistic pathogens. These include Burkholderia mallei and Burkholderia pseudomallei of the B. pseudomallei complex, which cause glanders and melioidosis, respectively. Burkholderia cenocepacia, Burkholderia multivorans, and Burkholderia vietnamiensis belong to the Burkholderia cepacia complex and affect mostly cystic fibrosis patients. Infections caused by these bacteria are difficult to treat because of significant antibiotic resistance. The first line of defense against antimicrobials in Burkholderia species is the outer membrane penetration barrier. Most Burkholderia contain a modified lipopolysaccharide that causes intrinsic polymyxin resistance. Contributing to reduced drug penetration are restrictive porin proteins. Efflux pumps of the resistance nodulation cell division family are major players in Burkholderia multidrug resistance. Third and fourth generation β-lactam antibiotics are seminal for treatment of Burkholderia infections, but therapeutic efficacy is compromised by expression of several β-lactamases and ceftazidime target mutations. Altered DNA gyrase and dihydrofolate reductase targets cause fluoroquinolone and trimethoprim resistance, respectively. Although antibiotic resistance hampers therapy of Burkholderia infections, the characterization of resistance mechanisms lags behind other non-enteric Gram-negative pathogens, especially ESKAPE bacteria such as Acinetobacter baumannii, Klebsiella pneumoniae and Pseudomonas aeruginosa.

Bloodstream infections after solid-organ transplantation

Solid-organ transplantation (SOT) has become the preferred strategy to treat a number of end-stage organ disease, because a continuous improvement in survival and quality of life. While preventive strategies has decreased the risk for classical opportunistic infections (such as viral, fungal and parasite infections), bacterial infections, and particularly bloodstream infections (BSIs) remain the most common and life-threatening complications in SOT recipients. The source of BSI after transplant depends on the type of transplantation, being urinary tract infection, pneumonia, and intraabdominal infections the most common infections occurring after kidney, lung and liver transplantation, respectively. The risk for candidemia is higher in abdominal-organ than in thoracic-organ transplantation. Currently, the increasing prevalence of multi-drug resistant (MDR) Gram-negative pathogens, such as extended-spectrum betalactamase-producing Enterobacteriaciae and carbapenem-resistant Klebsiella pneumoniae, is causing particular concerns in SOT recipients, a population which presents several risk factors for developing infections due to MDR organisms. The application of strict preventive policies to reduce the incidence of post transplant BSIs and to control the spread of MDR organisms, including the implementation of specific stewardship programs to avoid the overuse of antibiotics and antifungal drugs, are essential steps to reduce the impact of post transplant infections on allograft and patient outcomes.

Burkholderia cepacia Exit-Site Infection in Peritoneal Dialysis Patients-Clinical Characteristics and Treatment Outcomes

♦

BACKGROUND

Burkholderia cepacia is a hardy bacterium with intrinsic resistance to multiple antibiotics and high transmissibility. Opportunistic healthcare-associated B. cepacia infections among immunocompromised or critically ill patients have been reported, but there is limited data on the clinical characteristics and treatment outcomes of exit-site infection (ESI) in peritoneal dialysis (PD) patients. ♦

PATIENTS AND METHODS

Patients who suffered from B. cepacia ESI from 1 January 2004 to 31 December 2014 were reviewed. The clinical characteristics and treatment outcomes of the patients and the antibiotic susceptibility patterns of the bacterial isolates were analyzed. ♦

RESULTS

Twenty-two patients were included for analysis. Eight patients (36.4%) had medical conditions which impaired host immunity, while 7 (31.8%) had pre-existing skin abnormalities. Three patients (13.6%) progressed to tunnel-tract infection and another 3 patients (13.6%) developed associated peritonitis. Fifteen patients (68.2%) responded to medical treatment while 7 (31.8%) required catheter removal. Eleven patients (50.0%) had recurrent B. cepacia ESI, which occurred at 7.8 months (95% confidence interval [CI] 0.1 - 19.4 months) after the first episode. Most B. cepacia strains were susceptible to ceftazidime (95.5%), piperacillin/tazobactam (95.5%), and piperacillin (90.9%). Besides aminoglycosides (80 - 100%), high rates of resistance were also observed for ticarcillin/clavulanate (90.9%). ♦

CONCLUSION

Burkholderia cepacia ESI is associated with low rates of tunnel-tract infection or peritonitis, but the risk of recurrence is high. Most cases can be managed with medical treatment alone, although one third of patients might require catheter removal.

Lung transplantation for cystic fibrosis: results, indications, complications, and controversies

Survival in patients with cystic fibrosis (CF) has improved dramatically over the past 30 to 40 years, with mean survival now approximately 40 years. Nonetheless, progressive respiratory insufficiency remains the major cause of mortality in CF patients, and lung transplantation (LT) is eventually required. Timing of listing for LT is critical, because up to 25 to 41% of CF patients have died while awaiting LT. Globally, approximately 16.4% of lung transplants are performed in adults with CF. Survival rates for LT recipients with CF are superior to other indications, yet LT is associated with substantial morbidity and mortality (∼50% at 5-year survival rates). Myriad complications of LT include allograft failure (acute or chronic), opportunistic infections, and complications of chronic immunosuppressive medications (including malignancy). Determining which patients are candidates for LT is difficult, and survival benefit remains uncertain. In this review, we discuss when LT should be considered, criteria for identifying candidates, contraindications to LT, results post-LT, and specific complications that may be associated with LT. Infectious complications that may complicate CF (particularly Burkholderia cepacia spp., opportunistic fungi, and nontuberculous mycobacteria) are discussed.

Clinical and in vitro evidence for the antimicrobial therapy in Burkholderia cepacia complex infections

Treatment of infections caused by Burkholderia cepacia complex (Bcc) in cystic fibrosis (CF) patients poses a complex problem. Bcc is multidrug-resistant due to innate and acquired mechanisms of resistance. As CF patients receive multiple courses of antibiotics, susceptibility patterns of strains from CF patients may differ from those noted in strains from non-CF patients. Thus, there was a need for assessing in vitro and clinical data to guide antimicrobial therapy in these patients. A systematic search of literature, followed by extraction and analysis of available information from human and in vitro studies was done. The results of the analysis are used to address various aspects like use of antimicrobials for pulmonary and non-pulmonary infections, use of combination versus monotherapy, early eradication, duration of therapy, route of administration, management of biofilms, development of resistance during therapy, pharmacokinetics-pharmacodynamics correlations, therapy in post-transplant patients and newer drugs in Bcc-infected CF patients.

Bacterial Adaptation during Chronic Respiratory Infections

Chronic lung infections are associated with increased morbidity and mortality for individuals with underlying respiratory conditions such as cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD). The process of chronic colonisation allows pathogens to adapt over time to cope with changing selection pressures, co-infecting species and antimicrobial therapies. These adaptations can occur due to environmental pressures in the lung such as inflammatory responses, hypoxia, nutrient deficiency, osmolarity, low pH and antibiotic therapies. Phenotypic adaptations in bacterial pathogens from acute to chronic infection include, but are not limited to, antibiotic resistance, exopolysaccharide production (mucoidy), loss in motility, formation of small colony variants, increased mutation rate, quorum sensing and altered production of virulence factors associated with chronic infection. The evolution of Pseudomonas aeruginosa during chronic lung infection has been widely studied. More recently, the adaptations that other chronically colonising respiratory pathogens, including Staphylococcus aureus, Burkholderia cepacia complex and Haemophilus influenzae undergo during chronic infection have also been investigated. This review aims to examine the adaptations utilised by different bacterial pathogens to aid in their evolution from acute to chronic pathogens of the immunocompromised lung including CF and COPD.

Burkholderia cepacia complex Phage-Antibiotic Synergy (PAS): antibiotics stimulate lytic phage activity

The Burkholderia cepacia complex (Bcc) is a group of at least 18 species of Gram-negative opportunistic pathogens that can cause chronic lung infection in cystic fibrosis (CF) patients. Bcc organisms possess high levels of innate antimicrobial resistance, and alternative therapeutic strategies are urgently needed. One proposed alternative treatment is phage therapy, the therapeutic application of bacterial viruses (or bacteriophages). Recently, some phages have been observed to form larger plaques in the presence of sublethal concentrations of certain antibiotics; this effect has been termed phage-antibiotic synergy (PAS). Those reports suggest that some antibiotics stimulate increased production of phages under certain conditions. The aim of this study is to examine PAS in phages that infect Burkholderia cenocepacia strains C6433 and K56-2. Bcc phages KS12 and KS14 were tested for PAS, using 6 antibiotics representing 4 different drug classes. Of the antibiotics tested, the most pronounced effects were observed for meropenem, ciprofloxacin, and tetracycline. When grown with subinhibitory concentrations of these three antibiotics, cells developed a chain-like arrangement, an elongated morphology, and a clustered arrangement, respectively. When treated with progressively higher antibiotic concentrations, both the sizes of plaques and phage titers increased, up to a maximum. B. cenocepacia K56-2-infected Galleria mellonella larvae treated with phage KS12 and low-dose meropenem demonstrated increased survival over controls treated with KS12 or antibiotic alone. These results suggest that antibiotics can be combined with phages to stimulate increased phage production and/or activity and thus improve the efficacy of bacterial killing.

Pharmacokinetics and pharmacodynamics of aerosolized antibacterial agents in chronically infected cystic fibrosis patients

Bacteria adapt to growth in lungs of patients with cystic fibrosis (CF) by selection of heterogeneously resistant variants that are not detected by conventional susceptibility testing but are selected for rapidly during antibacterial treatment. Therefore, total bacterial counts and antibiotic susceptibilities are misleading indicators of infection and are not helpful as guides for therapy decisions or efficacy endpoints. High drug concentrations delivered by aerosol may maximize efficacy, as decreased drug susceptibilities of the pathogens are compensated for by high target site concentrations. However, reductions of the bacterial load in sputum and improvements in lung function were within the same ranges following aerosolized and conventional therapies. Furthermore, the use of conventional pharmacokinetic/pharmacodynamic (PK/PD) surrogates correlating pharmacokinetics in serum with clinical cure and presumed or proven eradication of the pathogen as a basis for PK/PD investigations in CF patients is irrelevant, as minimization of systemic exposure is one of the main objectives of aerosolized therapy; in addition, bacterial pathogens cannot be eradicated, and chronic infection cannot be cured. Consequently, conventional PK/PD surrogates are not applicable to CF patients. It is nonetheless obvious that systemic exposure of patients, with all its sequelae, is minimized and that the burden of oral treatment for CF patients suffering from chronic infections is reduced.