Novel antibiotic combinations proposed for treatment of Burkholderia cepacia complex infections

Acidic pH modulates Burkholderia cenocepacia antimicrobial susceptibility in the cystic fibrosis nutritional environment

IMPORTANCE

Burkholderia cenocepacia causes severe infections in cystic fibrosis (CF) patients. CF patients are prone to reoccurring infections due to the accumulation of mucus in their lungs, where bacteria can adhere and grow. Some of the antibiotics that inhibit B. cenocepacia in the laboratory are not effective for CF patients. A major contributor to poor clinical outcomes is that antibiotic testing in laboratories occurs under conditions that are different from those of sputum. CF sputum may be acidic and have increased concentrations of iron and zinc. Here, we used a medium that mimics CF sputum and found that acidic pH decreased the activity of many of the antibiotics used against B. cenocepacia. In addition, we assessed susceptibility to more than 500 antibiotics and found four active compounds against B. cenocepacia. Our findings give a better understanding of the lack of a relationship between susceptibility testing and the clinical outcome when treating B. cenocepacia infections.

Phage Milagro: a platform for engineering a broad host range virulent phage for Burkholderia

IMPORTANCE

Burkholderia infections are a significant concern in people with CF and other immunocompromising disorders, and are difficult to treat with conventional antibiotics due to their inherent drug resistance. Bacteriophages, or bacterial viruses, are now seen as a potential alternative therapy for these infections, but most of the naturally occurring phages are temperate and have narrow host ranges, which limit their utility as therapeutics. Here we describe the temperate Burkholderia phage Milagro and our efforts to engineer this phage into a potential therapeutic by expanding the phage host range and selecting for phage mutants that are strictly virulent. This approach may be used to generate new therapeutic agents for treating intractable infections in CF patients.

Polyamine as a microenvironment factor in resistance to antibiotics

One of the main issues in modern medicine is the decrease in the efficacy of antibiotic therapy against resistant microorganisms. The advent of antimicrobial resistance has added significantly to the impact of infectious diseases, in number of infections, as well as added healthcare costs. The development of antibiotic tolerance and resistance is influenced by a variety of environmental variables, and it is important to identify these environmental factors as part of any strategy for combating antibiotic resistance. The review aims to emphasize that biogenic polyamines are one of such environmental cues that impacts the antibiotic resistance in bacteria. The biogenic polyamines can help bacteria acquire resistance to antibiotics either by regulating the level of number of porin channels in the outer membrane, by modifying the outer membrane liposaccharides or by protecting macromolecule from antibiotic stress. Thus, understanding the way polyamines function in bacteria can thus be beneficial while designing the drugs to combat diseases.

Antibacterial Activity of a Natural Clay Mineral against Burkholderia cepacia Complex and Other Bacterial Pathogens Isolated from People with Cystic Fibrosis

There is an impending crisis in healthcare brought about by a new era of untreatable infections caused by bacteria resistant to all available antibiotics. Thus, there is an urgent need to identify novel antimicrobial agents to counter the continuing threat posed by formerly treatable infections. We previously reported that a natural mineral clay known as Kisameet clay (KC) is a potent inhibitor of the organisms responsible for acute infections. Chronic bacterial infections present another major challenge to treatment by antimicrobials, due to their prolonged nature, which results in repeated exposure to antibiotics and a constant selection for antimicrobial resistance. A prime example is bacteria belonging to the Burkholderia cepacia complex (Bcc), which particularly causes some of the most serious chronic lung infections in patients with cystic fibrosis (CF) associated with unpredictable clinical outcomes, poor prognosis, and high mortality rates. Eradication of these organisms from CF patients with limited effective antimicrobial options is a major challenge. Novel therapeutic approaches are urgently required. Here, we report the in vitro antibacterial activity of KC aqueous suspensions (1-10% w/v) and its aqueous extract (L100) against a collection of extensively and multi-drug resistant clinical isolates of Bcc, Pseudomonas aeruginosa, and Stenotrophomonas maltophilia isolated from patients with CF. These findings present a potential novel therapy for further investigation in the clinic.

Biofilm Targeting Strategy in the Eradication of Burkholderia Infections: A Mini-Review

Burkholderia are intracellular pathogenic bacteria which can produce biofilm. This biofilm protects the intracellular pathogenic bacteria from antibiotic treatment and the immunological system of the host. Therefore, this review aims to describe the capacity of Burkholderia to form a biofilm, the regulation of its biofilm formation, the efficacy of antibiotics to eradicate biofilm, and the novel therapy which targets its biofilm. Burkholderia's biofilm is characterized by its lipopolysaccharides, exopolysaccharides (EPSs), biofilm-associated proteins, and eDNA. Its regulation is made by quorum sensing, c-di-AMP, sRNA, and two component systems. Many antibiotics have been used as sole or mixture agents; however, they are not always effective in eradicating the biofilm-forming Burkholderia. Inhibitors of quorum sensing and other non-conventional antibiotic approaches are promising to discover effective treatment of Burkholderia infections.

Disruption of biofilms and killing of Burkholderia cenocepacia from cystic fibrosis lung using an antioxidant-antibiotic combination therapy

Cystic fibrosis (CF) is a disease caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR). The resulting chloride and bicarbonate imbalance produces a thick, static lung mucus. This mucus is not easily expelled from the lung and can be colonised by bacteria, leading to biofilm formation. CF lung infection with Burkholderia cepacia complex (BCC), particularly the subspecies B. cenocepacia, results in higher morbidity and mortality. Patients infected with BCC can rapidly progress to "cepacia syndrome", a fatal necrotising pneumonia. The aim of this study was to identify whether a combination therapy (CT) of selected antioxidants and antibiotics significantly disrupts B. cenocepacia biofilms and to determine the optimum CT level for treatment. Using controlled in vitro spectrophotometry, colony-forming unit and microscopy assays, three antioxidants (N-acetylcysteine [NAC], glutathione and vitamin C) and three antibiotics (ciprofloxacin, ceftazidime and tobramycin) were screened and assessed for their ability to disrupt the early and mature biofilms of six B. cenocepacia CF isolates. A combination of NAC and ciprofloxacin produced a statistically significant biofilm disruption in all strains tested, with growth inhibition (>5-8 log₁₀) observed when exposed to 4890 or 8150 μg/mL NAC in combination with 32 or 64 μg/mL ciprofloxacin. NAC-mediated biofilm disruption may be aided by the acidic pH of NAC at higher concentrations. This study showed that NAC is an effective disruptor that reduces the necessity for high concentrations of antibiotic. Further research will focus on the host toxicity and efficacy in ex vivo CF models.

Burkholderia ubonensis High-Level Tetracycline Resistance Is Due to Efflux Pump Synergy Involving a Novel TetA(64) Resistance Determinant

Burkholderia ubonensis, a nonpathogenic soil bacterium belonging to the Burkholderia cepacia complex (Bcc), is highly resistant to some clinically significant antibiotics. The concern is that B. ubonensis may serve as a resistance reservoir for Bcc or B. pseudomallei complex (Bpc) organisms that are opportunistic human pathogens. Using a B. ubonensis strain highly resistant to tetracycline (MIC, ≥256 µg/ml), we identified and characterized tetA(64) that encodes a novel tetracycline-specific efflux pump of the major facilitator superfamily. TetA(64) and associated TetR(64) regulator expression are induced by tetracyclines. Although TetA(64) is the primary tetracycline and doxycycline resistance determinant, maximum tetracycline and doxycycline resistance requires synergy between TetA(64) and the nonspecific AmrAB-OprA resistance nodulation cell division efflux pump. TetA(64) does not efflux minocycline, tigecycline, and eravacycline. Comprehensive screening of genome sequences showed that TetA(64) is unequally distributed in the Bcc and absent from the Bpc. It is present in some major cystic fibrosis pathogens, like Burkholderia cenocepacia, but absent from others like Burkholderia multivorans The tetR(64)-tetA(64) genes are located in a region of chromosome 1 that is highly conserved in Burkholderia sp. Because there is no evidence for transposition, the tetR(64)-tetA(64) genes may have been acquired by homologous recombination after horizontal gene transfer. Although Burkholderia species contain a resident multicomponent efflux pump that allows them to respond to tetracyclines up to a certain concentration, the acquisition of the single-component TetA(64) by some species likely provides the synergy that these bacteria need to defend against high tetracycline concentrations in niche environments.