Mycobacteroides abscessus ability to interact with the host mucosal cells plays an important role in pathogenesis of the infection

Non-tuberculous mycobacteria (NTM) are opportunistic pathogens ubiquitous in the environment. Mycobacteroides abscessus is a relatively new pathogen associated with underlying lung chronic pathologies, accounting for most of the pulmonary infections linked to the rapidly growing mycobacteria group. This includes chronic obstructive pulmonary disease, bronchiectasis, or cystic fibrosis. Patient outcomes from M. abscessus infections are poor due to complicated treatments and other factors. Intrinsic drug resistance plays an important role. The M. abscessus toolbox of resistance is varied leading to complex strategies for treatment. Mechanisms include waxy cell walls, drug export mechanisms, and acquired resistance. Many studies have also shown the impact of extracellular DNA found in the biofilm matrix during early infection and its possible advantage in pathogenicity. In this review, we discuss the current knowledge of early infection focusing on biofilm formation, an environmental strategy, and which treatments prevent its formation improving current antibiotic treatment outcomes in preliminary studies.

Insights on adsorption of pyocyanin in montmorillonite using molecular dynamics simulation

Pyocyanin is an important virulence factor in the resistance of Pseudomonas aeruginosa to antibiotics. Pyocyanin is a planar three ring aromatic molecule that occurs as zwitterionic (PYO) or protonated species (PYOH+). Our earlier studies have shown that montmorillonite, through adsorption and transformation, can inactivate both PYO and PYOH+ in the interlayer space. The objective of this study was to elucidate the interaction mechanisms between montmorillonite and the adsorbed pyocyanin and to characterize the structure of the pyocyanin-montmorillonite complex via molecular dynamics (MD) simulations. The MD simulations were performed for the complexes of hydrated Na-montmorillonite (HM) with (i) neutral pyocyanin (HMP) and (ii) protonated pyocyanin (HMPH); and dehydrated Na-montmorillonite (DM) with (iii) neutral pyocyanin (DMP) and (iv) protonated pyocyanin (DMPH). The simulations indicated that in dry conditions, both PYO and PYOH+ were well-ordered in the midplane of the interlayer of montmorillonite, with the three aromatic rings almost parallel to the basal surface and sandwiched in-between basal surface-adsorbed Na+ planes. In humid conditions, the pyocyanin and Na+ were solvated in the interlayer space and the pyocyanin was less ordered compared to dehydrated models. Ion-dipole interaction (Na-O) was the dominant interaction for the dehydrated complexes DMPH and DMP but the interaction was stronger in the latter. The Na-O ion-dipole interaction remained the dominant interaction in hydrated HMP while in HMPH, water outcompeted PYOH+ for Na+ resulting in water-Na interaction being the dominant interaction. These results revealed the arrangement of the two species of pyocyanin in the interlayer spaces of montmorillonite and the mechanism of interaction between the pyocyanin and montmorillonite.

P. aeruginosa interactions with other microbes in biofilms during co-infection

This review addresses the topic of biofilms, including their development and the interaction between different counterparts. There is evidence that various diseases, such as cystic fibrosis, otitis media, diabetic foot wound infections, and certain cancers, are promoted and aggravated by the presence of polymicrobial biofilms. Biofilms are composed by heterogeneous communities of microorganisms protected by a matrix of polysaccharides. The different types of interactions between microorganisms gives rise to an increased resistance to antimicrobials and to the host's defense mechanisms, with the consequent worsening of disease symptoms. Therefore, infections caused by polymicrobial biofilms affecting different human organs and systems will be discussed, as well as the role of the interactions between the gram-negative bacteria Pseudomonas aeruginosa, which is at the base of major polymicrobial infections, and other bacteria, fungi, and viruses in the establishment of human infections and diseases. Considering that polymicrobial biofilms are key to bacterial pathogenicity, it is fundamental to evaluate which microbes are involved in a certain disease to convey an appropriate and efficacious antimicrobial therapy.

Updated Review on the Mechanisms of Pathogenicity in Mycobacterium abscessus, a Rapidly Growing Emerging Pathogen

In recent years, Mycobacterium abscessus has appeared as an emerging pathogen, with an increasing number of disease cases reported worldwide that mainly occur among patients with chronic lung diseases or impaired immune systems. The treatment of this pathogen represents a challenge due to the multi-drug-resistant nature of this species and its ability to evade most therapeutic approaches. However, although predisposing host factors for disease are well known, intrinsic pathogenicity mechanisms of this mycobacterium are still not elucidated. Like other mycobacteria, intracellular invasiveness and survival inside different cell lines are pathogenic factors related to the ability of M. abscessus to establish infection. Some of the molecular factors involved in this process are well-known and are present in the mycobacterial cell wall, such as trehalose-dimycolate and glycopeptidolipids. The ability to form biofilms is another pathogenic factor that is essential for the development of chronic disease and for promoting mycobacterial survival against the host immune system or different antibacterial treatments. This capability also seems to be related to glycopeptidolipids and other lipid molecules, and some studies have shown an intrinsic relationship between both pathogenic mechanisms. Antimicrobial resistance is also considered a mechanism of pathogenicity because it allows the mycobacterium to resist antimicrobial therapies and represents an advantage in polymicrobial biofilms. The recent description of hyperpathogenic strains with the potential interhuman transmission makes it necessary to increase our knowledge of pathogenic mechanisms of this species to design better therapeutic approaches to the management of these infections.

Surface Motility Favors Codependent Interaction between Pseudomonas aeruginosa and Burkholderia cenocepacia

Interactions between different bacterial species shape bacterial communities and their environments. The opportunistic pathogens Pseudomonas aeruginosa and Burkholderia cenocepacia both can colonize the lungs of individuals affected by cystic fibrosis. Using the social surface behavior called swarming motility as a study model, we noticed intricate interactions between B. cenocepacia K56-2 and P. aeruginosa PA14. While strain K56-2 does not swarm under P. aeruginosa favorable swarming conditions, co-inoculation with a nonmotile PA14 flagellum-less ΔfliC mutant restored spreading for both strains. We show that P. aeruginosa provides the wetting agent rhamnolipids allowing K56-2 to perform swarming motility, while aflagellated PA14 appears to “hitchhike” along with K56-2 cells in the swarming colony.

IMPORTANCEPseudomonas aeruginosa and Burkholderia cenocepacia are important opportunistic pathogens often found together in the airways of persons with cystic fibrosis. Laboratory cocultures of both species often ends with one taking over the other. We used a surface motility assay to study the social interactions between populations of these bacterial species. Under our conditions, B. cenocepacia cannot swarm without supplementation of the wetting agent produced by P. aeruginosa. In a mixed colony of both species, an aflagellated mutant of P. aeruginosa provides the necessary wetting agent to B. cenocepacia, allowing both bacteria to swarm and colonize a surface. We highlight this peculiar interaction where both bacteria set aside their antagonistic tendencies to travel together.

Convergency and Stability Responses of Bacterial Communities to Salinization in Arid and Semiarid Areas: Implications for Global Climate Change in Lake Ecosystems

Climate change has given rise to salinization and nutrient enrichment in lake ecosystems of arid and semiarid areas, which have posed the bacterial communities not only into an ecotone in lake ecosystems but also into an assemblage of its own unique biomes. However, responses of bacterial communities to climate-related salinization and nutrient enrichment remain unclear. In September 2019, this study scrutinized the turnover of bacterial communities along gradients of increasing salinity and nutrient by a space-for-time substitution in Xinjiang Uyghur Autonomous Region, China. We find that salinization rather than nutrient enrichment primarily alters bacterial communities. The homogenous selection of salinization leads to convergent response of bacterial communities, which is revealed by the combination of a decreasing β-nearest taxon index (βNTI) and a pronounced negative correlation between niche breadth and salinity. Furthermore, interspecific interactions within bacterial communities significantly differed among distinct salinity levels. Specifically, mutualistic interactions showed an increase along the salinization. In contrast, topological parameters show hump-shaped curves (average degree and density) and sunken curves (modularity, density, and average path distance), the extremums of which all appear in the high-brackish environment, hinting that bacterial communities are comparatively stable at freshwater and brine environments but are unstable in moderately high-brackish lake.

Prospects of Inhaled Phage Therapy for Combatting Pulmonary Infections

With respiratory infections accounting for significant morbidity and mortality, the issue of antibiotic resistance has added to the gravity of the situation. Treatment of pulmonary infections (bacterial pneumonia, cystic fibrosis-associated bacterial infections, tuberculosis) is more challenging with the involvement of multi-drug resistant bacterial strains, which act as etiological agents. Furthermore, with the dearth of new antibiotics available and old antibiotics losing efficacy, it is prudent to switch to non-antibiotic approaches to fight this battle. Phage therapy represents one such approach that has proven effective against a range of bacterial pathogens including drug resistant strains. Inhaled phage therapy encompasses the use of stable phage preparations given via aerosol delivery. This therapy can be used as an adjunct treatment option in both prophylactic and therapeutic modes. In the present review, we first highlight the role and action of phages against pulmonary pathogens, followed by delineating the different methods of delivery of inhaled phage therapy with evidence of success. The review aims to focus on recent advances and developments in improving the final success and outcome of pulmonary phage therapy. It details the use of electrospray for targeted delivery, advances in nebulization techniques, individualized controlled inhalation with software control, and liposome-encapsulated nebulized phages to take pulmonary phage delivery to the next level. The review expands knowledge on the pulmonary delivery of phages and the advances that have been made for improved outcomes in the treatment of respiratory infections.

Fostering Innovation in the Treatment of Chronic Polymicrobial Cystic Fibrosis-Associated Infections Exploring Aspartic Acid and Succinic Acid as Ciprofloxacin Adjuvants

Cystic fibrosis (CF) disease provokes the accumulation of thick and viscous sputum in the lungs, favoring the development of chronic and polymicrobial infections. Pseudomonas aeruginosa is the main bacterium responsible for these chronic infections, and much of the difficulty involved in eradicating it is due to biofilm formation. However, this could be mitigated using adjuvant compounds that help or potentiate the antibiotic action. Therefore, the main goal of this study was to search for substances that function as adjuvants and also as biofilm-controlling compounds, preventing or dismantling P. aeruginosa biofilms formed in an in vitro CF airway environment. Dual combinations of compounds with subinhibitory (1 and 2 mg/L) and inhibitory concentrations (4 mg/L) of ciprofloxacin were tested to inhibit the bacterial growth and biofilm formation (prophylactic approach) and to eradicate 24-h-old P. aeruginosa populations, including planktonic cells and biofilms (treatment approach). Our results revealed that aspartic acid (Asp) and succinic acid (Suc) restored ciprofloxacin action against P. aeruginosa. Suc combined with 2 mg/L of ciprofloxacin (Suc-Cip) was able to eradicate bacteria, and Asp combined with 4 mg/L of ciprofloxacin (Asp–Cip) seemed to eradicate the whole 24-h-old populations, including planktonic cells and biofilms. Based on biomass depletion data, we noted that Asp induced cell death and Suc seemed somehow to block or reduce the expression of ciprofloxacin resistance. As far as we know, this kind of action had not been reported up till now. The presence of Staphylococcus aureus and Burkholderia cenocepacia did not affect the efficacy of the Asp–Cip and Suc–Cip therapies against P. aeruginosa and, also important, P. aeruginosa depletion from polymicrobial communities did not create a window of opportunity for these species to thrive. Rather the contrary, Asp and Suc also improved ciprofloxacin action against B. cenocepacia. Further studies on the cytotoxicity using lung epithelial cells indicated toxicity of Suc–Cip caused by the Suc. In conclusion, we provided evidences that Asp and Suc could be potential ciprofloxacin adjuvants to eradicate P. aeruginosa living within polymicrobial communities. Asp–Cip and Suc–Cip could be promising therapeutic options to cope with CF treatment failures.

Bacterial Community Interactions During Chronic Respiratory Disease

Chronic respiratory diseases including chronic rhinosinusitis, otitis media, asthma, cystic fibrosis, non-CF bronchiectasis, and chronic obstructive pulmonary disease are a major public health burden. Patients suffering from chronic respiratory disease are prone to persistent, debilitating respiratory infections due to the decreased ability to clear pathogens from the respiratory tract. Such infections often develop into chronic, life-long complications that are difficult to treat with antibiotics due to the formation of recalcitrant biofilms. The microbial communities present in the upper and lower respiratory tracts change as these respiratory diseases progress, often becoming less diverse and dysbiotic, correlating with worsening patient morbidity. Those with chronic respiratory disease are commonly infected with a shared group of respiratory pathogens including Haemophilus influenzae, Streptococcus pneumoniae, Staphylococcus aureus, Pseudomonas aeruginosa, and Moraxella catarrhalis, among others. In order to understand the microbial landscape of the respiratory tract during chronic disease, we review the known inter-species interactions among these organisms and other common respiratory flora. We consider both the balance between cooperative and competitive interactions in relation to microbial community structure. By reviewing the major causes of chronic respiratory disease, we identify common features across disease states and signals that might contribute to community shifts. As microbiome shifts have been associated with respiratory disease progression, worsening morbidity, and increased mortality, these underlying community interactions likely have an impact on respiratory disease state.

Intracellular Burkholderia Symbionts induce extracellular secondary infections; driving diverse host outcomes that vary by genotype and environment

Symbiotic associations impact and are impacted by their surrounding ecosystem. The association between Burkholderia bacteria and the soil amoeba Dictyostelium discoideum is a tractable model to unravel the biology underlying symbiont-endowed phenotypes and their impacts. Several Burkholderia species stably associate with D. discoideum and typically reduce host fitness in food-rich environments while increasing fitness in food-scarce environments. Burkholderia symbionts are themselves inedible to their hosts but induce co-infections with secondary bacteria that can serve as a food source. Thus, Burkholderia hosts are "farmers" that carry food bacteria to new environments, providing a benefit when food is scarce. We examined the ability of specific Burkholderia genotypes to induce secondary co-infections and assessed host fitness under a range of co-infection conditions and environmental contexts. Although all Burkholderia symbionts intracellularly infected Dictyostelium, we found that co-infections are predominantly extracellular, suggesting that farming benefits are derived from extracellular infection of host structures. Furthermore, levels of secondary infection are linked to conditional host fitness; B. agricolaris infected hosts have the highest level of co-infection and have the highest fitness in food-scarce environments. This study illuminates the phenomenon of co-infection induction across Dictyostelium associated Burkholderia species and exemplifies the contextual complexity of these associations.

Selective pressures during chronic infection drive microbial competition and cooperation

Chronic infections often contain complex mixtures of pathogenic and commensal microorganisms ranging from aerobic and anaerobic bacteria to fungi and viruses. The microbial communities present in infected tissues are not passively co-existing but rather actively interacting with each other via a spectrum of competitive and/or cooperative mechanisms. Competition versus cooperation in these microbial interactions can be driven by both the composition of the microbial community as well as the presence of host defense strategies. These interactions are typically mediated via the production of secreted molecules. In this review, we will explore the possibility that microorganisms competing for nutrients at the host–pathogen interface can evolve seemingly cooperative mechanisms by controlling the production of subsets of secreted virulence factors. We will also address interspecies versus intraspecies utilization of community resources and discuss the impact that this phenomenon might have on co-evolution at the host–pathogen interface.

Peptide modification results in the formation of a dimer with a 60-fold enhanced antimicrobial activity

Cationic antimicrobial peptides (CAMPs) occur naturally in numerous organisms and are considered as a class of antibiotics with promising potential against multi-resistant bacteria. Herein, we report a strategy that can lead to the discovery of novel small CAMPs with greatly enhanced antimicrobial activity and retained antibiofilm potential. We geared our efforts towards i) the N-terminal cysteine functionalization of a previously reported small synthetic cationic peptide (peptide 1037, KRFRIRVRV-NH2), ii) its dimerization through a disulfide bond, and iii) a preliminary antimicrobial activity assessment of the newly prepared dimer against Pseudomonas aeruginosa and Burkholderia cenocepacia, pathogens responsible for the formation of biofilms in lungs of individuals with cystic fibrosis. This dimer is of high interest as it does not only show greatly enhanced bacterial growth inhibition properties compared to its pep1037 precursor (up to 60 times), but importantly, also displays antibiofilm potential at sub-MICs. Our results suggest that the reported dimer holds promise for its use in future adjunctive therapy, in combination with clinically-relevant antibiotics.

Bacterial infections in patients with primary ciliary dyskinesia: Comparison with cystic fibrosis

Primary ciliary dyskinesia (PCD) is an autosomal recessive disorder associated with severely impaired mucociliary clearance caused by defects in ciliary structure and function. Although recurrent bacterial infection of the respiratory tract is one of the major clinical features of this disease, PCD airway microbiology is understudied. Despite the differences in pathophysiology, assumptions about respiratory tract infections in patients with PCD are often extrapolated from cystic fibrosis (CF) airway microbiology. This review aims to summarize the current understanding of bacterial infections in patients with PCD, including infections with Pseudomonas aeruginosa, Staphylococcus aureus, and Moraxella catarrhalis, as it relates to bacterial infections in patients with CF. Further, we will discuss current and potential future treatment strategies aimed at improving the care of patients with PCD suffering from recurring bacterial infections.

Synthetic cystic fibrosis sputum medium diminishes Burkholderia cenocepacia antifungal activity against Aspergillus fumigatus independently of phenylacetic acid production

Phenylacetic acid (PAA), an intermediate of phenylalanine degradation, is emerging as a signal molecule in microbial interactions with the host. In this work, we explore the presence of phenylalanine and PAA catabolism in 3 microbial pathogens of the cystic fibrosis (CF) lung microbiome: Pseudomonas aeruginosa, Burkholderia cenocepacia, and Aspergillus fumigatus. While in silico analysis of B. cenocepacia J2315 and A. fumigatus Af293 genome sequences showed complete pathways from phenylalanine to PAA, the P. aeruginosa PAO1 genome lacked several coding genes for phenylalanine and PAA catabolic enzymes. High-performance liquid chromatography analysis of supernatants from B. cenocepacia K56-2 detected PAA when grown in Luria-Bertani medium but not in synthetic cystic fibrosis sputum medium (SCFM). However, we were unable to identify PAA production by A. fumigatus or P. aeruginosa in any of the conditions tested. The inhibitory effect of B. cenocepacia on A. fumigatus growth was evaluated using agar plate interaction assays. Inhibition of fungal growth by B. cenocepacia was lessened in SCFM but this effect was not dependent on bacterial production of PAA. In summary, while we demonstrated PAA production by B. cenocepacia, we were not able to link this metabolite with the B. cenocepacia - A. fumigatus microbial interaction in CF nutritional conditions.

Microbiome in the pathogenesis of cystic fibrosis and lung transplant-related disease

Significant advances in culture-independent methods have expanded our knowledge about the diversity of the lung microbial environment. Complex microorganisms and microbial communities can now be identified in the distal airways in a variety of respiratory diseases, including cystic fibrosis (CF) and the posttransplantation lung. Although there are significant methodologic concerns about sampling the lung microbiome, several studies have now shown that the microbiome of the lower respiratory tract is distinct from the upper airway. CF is a disease characterized by chronic airway infections that lead to significant morbidity and mortality. Traditional culture-dependent methods have identified a select group of pathogens that cause exacerbations in CF, but studies using bacterial 16S rRNA gene-based microarrays have shown that the CF microbiome is an intricate and dynamic bacterial ecosystem, which influences both host immune health and disease pathogenesis. These microbial communities can shift with external influences, including antibiotic exposure. In addition, there have been a number of studies suggesting a link between the gut microbiome and respiratory health in CF. Compared with CF, there is significantly less knowledge about the microbiome of the transplanted lung. Risk factors for bronchiolitis obliterans syndrome, one of the leading causes of death, include microbial infections. Lung transplant patients have a unique lung microbiome that is different than the pretransplanted microbiome and changes with time. Understanding the host-pathogen interactions in these diseases may suggest targeted therapies and improve long-term survival in these patients.

Clinical Insights into Pulmonary Exacerbations in Cystic Fibrosis from the Microbiome. What Are We Missing?

Pulmonary exacerbations account for much of the decrease in lung function and consequently most of the morbidity and mortality in patients with cystic fibrosis. These events are driven by an acute inflammatory response to infection. Recent technological advancements in molecular profiling techniques have allowed for a proliferation of microbiome studies of the lower airways of patients with cystic fibrosis. But these methods may not provide a comprehensive and unbiased measure of the lung microbiota in these patients and molecular profiles do not always translate to quantitative microbiology. Furthermore, these studies have not yet been able to provide much in the way of mechanistic insights into exacerbations or to guide patient therapy. We propose a model in which pulmonary exacerbations may be driven by an active subpopulation of the lung microbiota, which may represent only a small portion of the microbiota measured in a clinical sample. Methodology should be focused on the ultimate goal, which is to use the best available approaches to provide accurate quantitative measures of the microbiome to inform clinical decisions and provide rapid assessment of treatment efficacy. These strategies would be relevant to other chronic lung diseases such as chronic obstructive pulmonary disease and neutrophilic asthma.

Cyanide Toxicity to Burkholderia cenocepacia Is Modulated by Polymicrobial Communities and Environmental Factors

Microbes within polymicrobial communities can establish positive and negative interactions that have the potential to influence the overall behavior of the community. Pseudomonas aeruginosa and species of the Burkholderia cepacia complex (Bcc) can co-exist in the lower airways, however several studies have shown that P. aeruginosa can effectively kill the Bcc in vitro, for which hydrogen cyanide (HCN) was recently proposed to play a critical role. Here we show that modification of the environment (i.e., culture medium), long-term genetic adaptation of P. aeruginosa to the cystic fibrosis (CF) lung, or the addition of another bacterial species to the community can alter the sensitivity of Burkholderia cenocepacia to P. aeruginosa toxins. We specifically demonstrate that undefined rich media leads to higher susceptibility of B. cenocepacia to P. aeruginosa toxins like cyanide as compared to a synthetic medium (SCFM), that mimics the CF lung nutritional content. Overall, our study shows that the polymicrobial environment can have profound effects on negative interactions mediated by P. aeruginosa against B. cenocepacia. In fact, evolved P. aeruginosa or the presence of other species such as Staphylococcus aureus can directly abolish the direct competition mediated by cyanide and consequently maintaining a higher level of species diversity within the community.

Antimicrobial susceptibility of hospital acquired Stenotrophomonas maltophilia isolate biofilms

AIMS

We sought to characterize the antibiotic susceptibility of strains of Stenotrophomonas maltophilia isolated from clinical samples, and the role of Stenotrophomonas maltophilia biofilm in antibiotic resistance.

METHODS

Fifty-one clinical Stenotrophomonas maltophilia isolates were obtained from patients with nosocomial infection in the surgical wards and ICUs of six general hospitals in Tianjin, China. In vitro models of Stenotrophomonas maltophilia biofilms were established and confirmed by scanning electron microscopy and fluorescence microscopy with silver staining. The minimal inhibitory concentrations and biofilm inhibitory concentrations of commonly used antibiotics were determined.

RESULTS

47 of 51 strains were resistant to three or more antibiotics. 42 of 51 strains formed Stenotrophomonas maltophilia biofilms in vitro. Stenotrophomonas maltophilia biofilm formation greatly reduced sensitivity to most tested antibiotics, but not to levofloxacin. However, in the presence of erythromycin scanning electron microscopy revealed that levofloxacin inhibited Stenotrophomonas maltophilia biofilm formation. Factorial ANOVA revealed that erythromycin enhanced susceptibility to levofloxacin, cefoperazone/sulbactam, and piperacillin (p<0.05), and an ΔE model revealed that levofloxacin and erythromycin acted synergistically in biofilms, suggesting specific use of combined macrolide therapy may represent an effective treatment for Stenotrophomonas maltophilia infection.

CONCLUSIONS

Antibiotics could act synergistically to combat the protection conferred to clinical isolates of Stenotrophomonas maltophilia by biofilms. Macrolide antibiotics may be effective where used in combination.

Development of a competitive binding assay for the Burkholderia cenocepacia lectin BC2L-A and structure activity relationship of natural and synthetic inhibitors

Burkholderia cenocepacia is an opportunistic Gram-negative pathogen and especially hazardous for cystic fibrosis patients.

Complete Genome Sequence of Burkholderia cepacia Strain LO6

Burkholderia cepacia strain LO6 is a betaproteobacterium that was isolated from a cystic fibrosis patient. Here we report the 6.4 Mb draft genome sequence assembled into 2 contigs. This genome sequence will aid the transcriptomic profiling of this bacterium and help us to better understand the mechanisms specific to pulmonary infections.

Localization of Burkholderia cepacia complex bacteria in cystic fibrosis lungs and interactions with Pseudomonas aeruginosa in hypoxic mucus

The localization of Burkholderia cepacia complex (Bcc) bacteria in cystic fibrosis (CF) lungs, alone or during coinfection with Pseudomonas aeruginosa, is poorly understood. We performed immunohistochemistry for Bcc and P. aeruginosa bacteria on 21 coinfected or singly infected CF lungs obtained at transplantation or autopsy. Parallel in vitro experiments examined the growth of two Bcc species, Burkholderia cenocepacia and Burkholderia multivorans, in environments similar to those occupied by P. aeruginosa in the CF lung. Bcc bacteria were predominantly identified in the CF lung as single cells or small clusters within phagocytes and mucus but not as "biofilm-like structures." In contrast, P. aeruginosa was identified in biofilm-like masses, but densities appeared to be reduced during coinfection with Bcc bacteria. Based on chemical analyses of CF and non-CF respiratory secretions, a test medium was defined to study Bcc growth and interactions with P. aeruginosa in an environment mimicking the CF lung. When test medium was supplemented with alternative electron acceptors under anaerobic conditions, B. cenocepacia and B. multivorans used fermentation rather than anaerobic respiration to gain energy, consistent with the identification of fermentation products by high-performance liquid chromatography (HPLC). Both Bcc species also expressed mucinases that produced carbon sources from mucins for growth. In the presence of P. aeruginosa in vitro, both Bcc species grew anaerobically but not aerobically. We propose that Bcc bacteria (i) invade a P. aeruginosa-infected CF lung when the airway lumen is anaerobic, (ii) inhibit P. aeruginosa biofilm-like growth, and (iii) expand the host bacterial niche from mucus to also include macrophages.

Pyocyanin stimulates quorum sensing-mediated tolerance to oxidative stress and increases persister cell populations in Acinetobacter baumannii

Acinetobacter baumannii and Pseudomonas aeruginosa are nosocomial pathogens with overlapping sites of infection. This work reports that the two can coexist stably in mixed-culture biofilms. In a study intended to improve our understanding of the mechanism of their coexistence, it was found that pyocyanin, produced by P. aeruginosa that generally eliminates competition from other pathogens, led to the generation of reactive oxygen species (ROS) in A. baumannii cells, which in response showed a significant (P ≤ 0.05) increase in production of enzymes, specifically, catalase and superoxide dismutase (SOD). This work shows for the first time that the expression of catalase and SOD is under the control of a quorum-sensing system in A. baumannii. In support of this observation, a quorum-sensing mutant of A. baumannii (abaI::Km) was found to be sensitive to pyocyanin compared to its wild type and showed significantly (P ≤ 0.001) lower levels of the antioxidant enzymes, which increased on addition of 5 μM N-(3-hydroxydodecanoyl)-l-homoserine lactone. Likewise, in wild-type A. baumannii, there was a significant (P < 0.01) decrease in the level of anti-oxidant enzymes in the presence of salicylic acid, a known quencher of quorum sensing. In the presence of amikacin and carbenicillin, A. baumannii formed 0.07 and 0.02% persister cells, which increased 4- and 3-fold, respectively, in the presence of pyocyanin. These findings show that pyocyanin induces a protective mechanism in A. baumannii against oxidative stress and also increases its persistence against antibiotics which could be of clinical significance in the case of coinfections with A. baumannii and P. aeruginosa.

Microbiome in cystic fibrosis: Shaping polymicrobial interactions for advances in antibiotic therapy

Recent molecular methodologies have demonstrated a complex microbial ecosystem in cystic fibrosis (CF) airways, with a wide array of uncommon microorganisms co-existing with the traditional pathogens. Although there are lines of evidence supporting the contribution of some of those emergent species for lung disease chronicity, clinical significance remains uncertain for most cases. A possible contribution for disease is likely to be related with the dynamic interactions established between microorganisms within the microbial community and with the host. If this is the case, management of CF will only be successful upon suitable and exhaustive modulation of such mixed ecological processes, which will also be useful to predict the effects of new therapeutic interventions.

MrkD1P from Klebsiella pneumoniae strain IA565 allows for coexistence with Pseudomonas aeruginosa and protection from protease-mediated biofilm detachment

Biofilm formation and persistence are essential components for the continued survival of pathogens inside the host and constitute a major contributor to the development of chronic wounds with resistance to antimicrobial compounds. Understanding these processes is crucial for control of biofilm-mediated disease. Though chronic wound infections are often polymicrobial in nature, much of the research on chronic wound-related microbes has focused on single-species models. Klebsiella pneumoniae and Pseudomonas aeruginosa are microbes that are often found together in wound isolates and are able to form stable in vitro biofilms, despite the antagonistic nature of P. aeruginosa with other organisms. Mutants of the K. pneumoniae strain IA565 lacking the plasmid-borne mrkD1P gene were less competitive than the wild type in an in vitro dual-species biofilm model with P. aeruginosa (PAO1). PAO1 spent medium inhibited the formation of biofilm of mrkD1P-deficient mutants and disrupted preestablished biofilms, with no effect on IA565 and no effect on the growth of the wild type or mutants. A screen using a two-allele PAO1 transposon library identified the LasB elastase as the secreted effector involved in biofilm disruption, and a purified version of the protein produced results similar to those with PAO1 spent medium. Various other proteases had a similar effect, suggesting that the disruption of the mrkD1P gene causes sensitivity to general proteolytic effects and indicating a role for MrkD1P in protection against host antibiofilm effectors. Our results suggest that MrkD1P allows for competition of K. pneumoniae with P. aeruginosa in a mixed-species biofilm and provides defense against microbial and host-derived proteases.

Interactions of Pseudomonas aeruginosa in predominant biofilm or planktonic forms of existence in mixed culture with Escherichia coli in vitro

Pseudomonas aeruginosa and Escherichia coli are known to be involved in mixed communities in diverse niches. In this study we examined the influence of the predominant form of cell existence of and the exometabolite production by P. aeruginosa strains on interspecies interactions, in vitro. Bacterial numbers of P. aeruginosa and E. coli in mixed plankton cultures and biofilms compared with their numbers in single plankton cultures and biofilms changed in a different way, but were in accordance with the form of P. aeruginosa cell existence. The mass of a mixed-species biofilm was greater than the mass of a single-species biofilm. Among the mixed biofilms, the one with the "planktonic" P. aeruginosa strain had the least biomass. The total pyocyanin and pyoverdin levels were found to be lower in all mixed plankton cultures. Despite this, clinical P. aeruginosa strains irrespective of the predominant form of existence ("biofilm" or "planktonic") had a higher total concentration of exometabolites than did the reference strain in 12-24 h mixed cultures. The metabolism of E. coli, according to its bioluminescence, was reduced in mixed cultures, and the decrease was by 20- to 100-fold greater with the clinical Pseudomonas strains than the reference Pseudomonas strain. Thus, both the predominant form of existence of and the exometabolite production by distinct P. aeruginosa strains should be considered to fully understand the interspecies relationship and bacteria survival in natural communities.

Photodynamic therapy of antibiotic-resistant biofilms in a maxillary sinus model

BACKGROUND

Chronic rhinosinusitis (CRS) is one of the most common chronic conditions in the United States. There is a significant subpopulation of CRS patients who remain resistant to cure despite rigorous treatment regimens including surgery, allergy therapy, and prolonged antibiotic therapy. Antimicrobial photodynamic therapy (aPDT) is a noninvasive nonantibiotic broad spectrum antimicrobial treatment. Our previous in vitro studies demonstrated that aPDT reduced CRS polymicrobial planktonic bacteria and fungi by >99.9% after a single treatment. However, prior to human treatment, the effectiveness of aPDT to eradicate polymicrobial biofilms in a maxillary sinus cavity must be demonstrated. The objective of this study was to demonstrate the effectiveness of a noninvasive aPDT treatment of antibiotic resistant biofilms known to cause CRS in a novel anatomically correct maxillary sinus in vitro model using an enhanced photosensitizer solution.

METHODS

Antibiotic resistant polymicrobial biofilms of Pseudomonas aeruginosa and methicillin-resistant Staphylococcus aureus (MRSA) were grown in an anatomically correct novel maxillary sinus model and treated with a methylene blue/ethylenediamine tetraacetic acid (EDTA) photosensitizer and 670-nm nonthermal activating light. Cultures of the biofilms were obtained before and after light treatment to determine efficacy of biofilm reduction.

RESULTS

The in vitro maxillary sinus CRS biofilm study demonstrated that aPDT reduced the CRS polymicrobial biofilm by >99.99% after a single treatment.

CONCLUSION

aPDT can effectively treat CRS polymicrobial antibiotic resistant Pseudomonas aeruginosa and MRSA biofilms in a maxillary sinus cavity model.

Modelling co-infection of the cystic fibrosis lung by Pseudomonas aeruginosa and Burkholderia cenocepacia reveals influences on biofilm formation and host response

The Gram-negative bacteria Pseudomonas aeruginosa and Burkholderia cenocepacia are opportunistic human pathogens that are responsible for severe nosocomial infections in immunocompromised patients and those suffering from cystic fibrosis (CF). These two bacteria have been shown to form biofilms in the airways of CF patients that make such infections more difficult to treat. Only recently have scientists begun to appreciate the complicated interplay between microorganisms during polymicrobial infection of the CF airway and the implications they may have for disease prognosis and response to therapy.

To gain insight into the possible role that interaction between strains of P. aeruginosa and B. cenocepacia may play during infection, we characterised co-inoculations of in vivo and in vitro infection models. Co-inoculations were examined in an in vitro biofilm model and in a murine model of chronic infection. Assessment of biofilm formation showed that B. cenocepacia positively influenced P. aeruginosa biofilm development by increasing biomass. Interestingly, co-infection experiments in the mouse model revealed that P. aeruginosa did not change its ability to establish chronic infection in the presence of B. cenocepacia but co-infection did appear to increase host inflammatory response.

Taken together, these results indicate that the co-infection of P. aeruginosa and B. cenocepacia leads to increased biofilm formation and increased host inflammatory response in the mouse model of chronic infection. These observations suggest that alteration of bacterial behavior due to interspecies interactions may be important for disease progression and persistent infection.

Proteases, cystic fibrosis and the epithelial sodium channel (ENaC)

Proteases perform a diverse array of biological functions. From simple peptide digestion for nutrient absorption to complex signaling cascades, proteases are found in organisms from prokaryotes to humans. In the human airway, proteases are associated with the regulation of the airway surface liquid layer, tissue remodeling, host defense and pathogenic infection and inflammation. A number of proteases are released in the airways under both physiological and pathophysiological states by both the host and invading pathogens. In airway diseases such as cystic fibrosis, proteases have been shown to be associated with increased morbidity and airway disease progression. In this review, we focus on the regulation of proteases and discuss specifically those proteases found in human airways. Attention then shifts to the epithelial sodium channel (ENaC), which is regulated by proteolytic cleavage and that is considered to be an important component of cystic fibrosis disease. Finally, we discuss bacterial proteases, in particular, those of the most prevalent bacterial pathogen found in cystic fibrosis, Pseudomonas aeruginosa.

N-acyl homoserine lactone mediated interspecies interactions between A. baumannii and P. aeruginosa

Acinetobacter baumannii and Pseudomonas aeruginosa are pathogens capable of colonizing the same infection sites and employing N-acyl homoserine lactone (AHL) based quorum-sensing systems to co-ordinate biofilm formation. Hence, the effect of P. aeruginosa AHLs on biofilm formation by A. baumannii and vice versa were investigated using the biofilm impaired quorum sensing mutants, A. baumannii M2 (abaI::Km) and P. aeruginosa PAO-JP2. Complementing the mutants with heterologous, extracted and pure AHLs increased biofilm mass significantly. The surface area coverage and biovolume also increased significantly as observed by confocal scanning laser microscopy which corroborated scanning electron microscope analysis. Autoinducer synthase gene promoters of A. baumannii, P( abaI)-lacZ, and P. aeruginosa, P( lasI)-lacZ, were induced (p < 0.05) by heterologous AHLs. Growth of A. baumannii was not inhibited by pyocyanin of P. aeruginosa which may allow their co-existence and interaction in the clinical setting, thereby affecting the severity of combined infections and therapeutic measures to control them.

Polymicrobial interactions: impact on pathogenesis and human disease

Microorganisms coexist in a complex milieu of bacteria, fungi, archaea, and viruses on or within the human body, often as multifaceted polymicrobial biofilm communities at mucosal sites and on abiotic surfaces. Only recently have we begun to appreciate the complicated biofilm phenotype during infection; moreover, even less is known about the interactions that occur between microorganisms during polymicrobial growth and their implications in human disease. Therefore, this review focuses on polymicrobial biofilm-mediated infections and examines the contribution of bacterial-bacterial, bacterial-fungal, and bacterial-viral interactions during human infection and potential strategies for protection against such diseases.

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.

Social interactions in the Burkholderia cepacia complex: biofilms and quorum sensing

Burkholderia cepacia complex bacteria are opportunistic pathogens that cause respiratory tract infections in susceptible patients, mainly people with cystic fibrosis. There is convincing evidence that B. cepacia complex bacteria can form biofilms, not only on abiotic surfaces (e.g., glass and plastics), but also on biotic surfaces such as epithelial cells, leading to the suggestion that biofilm formation plays a key role in persistent infection of cystic fibrosis lungs. This article presents an overview of the molecular mechanisms involved in B. cepacia complex biofilm formation, the increased resistance of sessile B. cepacia complex cells and the role of quorum sensing in B. cepacia complex biofilm formation.

Microtiter susceptibility testing of microbes growing on peg lids: a miniaturized biofilm model for high-throughput screening

Batch culture of biofilms on peg lids is a versatile method that can be used for microtiter determinations of biofilm antimicrobial susceptibility. In this paper, we describe a core protocol and a set of parameters (surface composition, the rate of rocking or orbital motion, temperature, cultivation time, inoculum size, atmospheric gases and nutritional medium) that can be adjusted to grow single- or multispecies biofilms on peg surfaces. Mature biofilms formed on peg lids can then be fitted into microtiter plates containing test agents. After a suitable exposure time, biofilm cells are disrupted into a recovery medium using sonication. Microbicidal endpoints can be determined qualitatively using optical density measurements or quantitatively using viable cell counting. Once equipment is calibrated and growth conditions are at an optimum, the procedure requires approximately 5 h of work over 4-6 d. This efficient method allows antimicrobial agents and exposure conditions to be tested against biofilms on a high-throughput scale.

Identification of Burkholderia cepacia complex bacteria with a lipopolysaccharide-specific monoclonal antibody

The genus Burkholderia includes many bacteria that cause serious human infections. As is the case with other Gram-negative bacteria, Burkholderia species produce LPS, which is an abundant component of the bacterial cell surface. Burkholderia cepacia complex (Bcc) bacteria (which include at least 17 separate species) produce LPS structures that are quite different. In an attempt to determine the degree of LPS epitope variation among Bcc species, a mAb was produced, designated 5D8, specific for the LPS of B. cepacia. Western blot analysis determined that mAb 5D8 was able to produce the classic 'ladder pattern' when used to probe B. cepacia and Burkholderia anthina lysates, although 5D8 did not produce this pattern with the other seven Bcc species tested. mAb 5D8 reacted with varying intensity to most but not all of the additional B. cepacia and B. anthina strains tested. Therefore, there seems to be significant epitope variation among Bcc LPS both between and within species. Additionally, mAb 5D8 reacted with a proteinase-K-sensitive 22 kDa antigen in all Bcc strains and also in a strain of Burkholderia pseudomallei.

Enhanced biofilm formation and 3-chlorobenzoate degrading activity by the bacterial consortium of Burkholderia sp. NK8 and Pseudomonas aeruginosa PAO1

AIMS

To characterize biofilm formation of a chlorobenzoates (CBs) degrading bacterium, Burkholderia sp. NK8, with another bacterial species, and the biodegradation activity against CBs in the mixed-species biofilm.

METHODS AND RESULTS

Burkholderia sp. NK8 was solely or co-cultured with each of five other representative bacteria in microtitre dishes. Biofilm formation involving the strain NK8 was synergistically promoted by co-culturing with only Pseudomonas aeruginosa PAO1. Epifluorescent microscopy revealed that cells of the bacterial strain NK8 were viable and distributed randomly in the mixed-species biofilms. Enumeration of the attached cells on the surface of wells revealed that cells of the strain NK8 increased approx. 10-fold by the co-culture with the strain PAO1 compared to those by monoculture of the strain NK8, and the degradation activity of 3-chlorobenzoate by the dual-species biofilms was more promoted than that by the strain NK8-monocultured biofilms.

CONCLUSIONS

Enhanced biofilm formation of Burkholderia sp. NK8 by the bacterial consortium occurred, but is determined by the partner bacterial species. The mixed-species biofilms have the advantage to degrade CBs on a solid surface.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study provides a significance of bacterial consortia on the biofilm formation and the degradation activity of Burkholderia sp. NK8, which contribute for complete degradation of chlorinated aromatics.

Bacteria of the Burkholderia cepacia complex are cyanogenic under biofilm and colonial growth conditions

BACKGROUND

The Burkholderia cepacia complex (Bcc) is a collection of nine genotypically distinct but phenotypically similar species. They show wide ecological diversity and include species that are used for promoting plant growth and bio-control as well species that are opportunistic pathogens of vulnerable patients. Over recent years the Bcc have emerged as problematic pathogens of the CF lung. Pseudomonas aeruginosa is another important CF pathogen. It is able to synthesise hydrogen cyanide (HCN), a potent inhibitor of cellular respiration. We have recently shown that HCN production by P. aeruginosa may have a role in CF pathogenesis. This paper describes an investigation of the ability of bacteria of the Bcc to make HCN.

RESULTS

The genome of Burkholderia cenocepacia has 3 putative HCN synthase encoding (hcnABC) gene clusters. B. cenocepacia and all 9 species of the Bcc complex tested were able to make cyanide at comparable levels to P. aeruginosa, but only when grown surface attached as colonies or during biofilm growth on glass beads. In contrast to P. aeruginosa and other cyanogenic bacteria, cyanide was not detected during planktonic growth of Bcc strains.

CONCLUSION

All species in the Bcc are cyanogenic when grown as surface attached colonies or as biofilms.

Frequency of cytokine gene promoter polymorphisms in the Northern Ireland Cystic Fibrosis population

It has been postulated that cytokine allele frequencies are gender and perhaps geographically-specific. Cytokine release is crucial in the regulation of the type and magnitude of the immune response. This study observed no differences in the frequency of cytokine promoter polymorphisms associated with variant levels of expression in patients with CF and a non-CF population of Northern Ireland.

High-throughput metal susceptibility testing of microbial biofilms

BACKGROUND

Microbial biofilms exist all over the natural world, a distribution that is paralleled by metal cations and oxyanions. Despite this reality, very few studies have examined how biofilms withstand exposure to these toxic compounds. This article describes a batch culture technique for biofilm and planktonic cell metal susceptibility testing using the MBEC assay. This device is compatible with standard 96-well microtiter plate technology. As part of this method, a two part, metal specific neutralization protocol is summarized. This procedure minimizes residual biological toxicity arising from the carry-over of metals from challenge to recovery media. Neutralization consists of treating cultures with a chemical compound known to react with or to chelate the metal. Treated cultures are plated onto rich agar to allow metal complexes to diffuse into the recovery medium while bacteria remain on top to recover. Two difficulties associated with metal susceptibility testing were the focus of two applications of this technique. First, assays were calibrated to allow comparisons of the susceptibility of different organisms to metals. Second, the effects of exposure time and growth medium composition on the susceptibility of E. coli JM109 biofilms to metals were investigated.

RESULTS

This high-throughput method generated 96-statistically equivalent biofilms in a single device and thus allowed for comparative and combinatorial experiments of media, microbial strains, exposure times and metals. By adjusting growth conditions, it was possible to examine biofilms of different microorganisms that had similar cell densities. In one example, Pseudomonas aeruginosa ATCC 27853 was up to 80 times more resistant to heavy metalloid oxyanions than Escherichia coli TG1. Further, biofilms were up to 133 times more tolerant to tellurite (TeO3(2-)) than corresponding planktonic cultures. Regardless of the growth medium, the tolerance of biofilm and planktonic cell E. coli JM109 to metals was time-dependent.

CONCLUSION

This method results in accurate, easily reproducible comparisons between the susceptibility of planktonic cells and biofilms to metals. Further, it was possible to make direct comparisons of the ability of different microbial strains to withstand metal toxicity. The data presented here also indicate that exposure time is an important variable in metal susceptibility testing of bacteria.

The multifarious, multireplicon Burkholderia cepacia complex

The Burkholderia cepacia complex (Bcc) is a collection of genetically distinct but phenotypically similar bacteria that are divided into at least nine species. Bcc bacteria are found throughout the environment, where they can have both beneficial and detrimental effects on plants and some members can also degrade natural and man-made pollutants. Bcc bacteria are now recognized as important opportunistic pathogens that can cause variable lung infections in cystic fibrosis patients, which result in asymptomatic carriage, chronic infection or 'cepacia syndrome', which is characterized by a rapid decline in lung function that can include invasive disease. Here we highlight the unique characteristics of the Bcc, focusing on the factors that determine virulence.

Identification of Burkholderia cenocepacia genes required for bacterial survival in vivo

Burkholderia cenocepacia (formerly Burkholderia cepacia complex genomovar III) causes chronic lung infections in patients with cystic fibrosis. In this work, we used a modified signature-tagged mutagenesis (STM) strategy for the isolation of B. cenocepacia mutants that cannot survive in vivo. Thirty-seven specialized plasposons, each carrying a unique oligonucleotide tag signature, were constructed and used to examine the survival of 2,627 B. cenocepacia transposon mutants, arranged in pools of 37 unique mutants, after a 10-day lung infection in rats by using the agar bead model. The recovered mutants were screened by real-time PCR, resulting in the identification of 260 mutants which presumably did not survive within the lungs. These mutants were repooled into smaller pools, and the infections were repeated. After a second screen, we isolated 102 mutants unable to survive in the rat model. The location of the transposon in each of these mutants was mapped within the B. cenocepacia chromosomes. We identified mutations in genes involved in cellular metabolism, global regulation, DNA replication and repair, and those encoding bacterial surface structures, including transmembrane proteins and cell surface polysaccharides. Also, we found 18 genes of unknown function, which are conserved in other bacteria. A subset of 12 representative mutants that were individually examined using the rat model in competition with the wild-type strain displayed reduced survival, confirming the predictive value of our STM screen. This study provides a blueprint to investigate at the molecular level the basis for survival and persistence of B. cenocepacia within the airways.

Green and red fluorescent protein vectors for use in biofilm studies of the intrinsically resistant Burkholderia cepacia complex

Cystic fibrosis isolates of the Burkholderia cepacia complex (BCC) have demonstrated a propensity to associate intimately with Pseudomonas aeruginosa in mixed community biofilms, which may impact on their overall pathogenicity during infection of the lungs in cystic fibrosis. Here, we describe the construction and use of novel green and red fluorescent protein expression vectors suitable for labeling biofilm cells of multi-resistant clinical isolates of the BCC for microscopic analysis of both single species biofilms and mixed community associations with P. aeruginosa. Antimicrobial susceptibility testing established that tetracycline and/or trimethoprim were suitable selective agents for widespread use in BCC. The green and red fluorescent protein genes, driven by constitutively active promoters, were cloned into two mobilizable plasmids pBBR1MCS-3 and pBBR1Tp, carrying tetracycline and trimethoprim resistance cassettes, respectively. The fluorescence of transformed BCC and P. aeruginosa planktonic cells was detectable using fluorescence microscopy and/or fluorometry. The plasmids were stable in the absence of selection for at least 3 days in planktonic and biofilm cultures, and fluorescence was still visible in a 4-day glass coverslip flow cell biofilm. The plasmids functioned well to distinguish the two species in a mixed community biofilm, with no indications of plasmid transfer between species or cross-talk of the fluorescent signals. These vectors represent the first green and red fluorescent vectors to be constructed and analyzed specifically for wide spread use in BCC and P. aeruginosa single and mixed biofilm cultures.

Interspecies communication between Burkholderia cepacia and Pseudomonas aeruginosa

Burkholderia cepacia and Pseudomonas aeruginosa are opportunistic pathogens that commonly cause pulmonary infections in cystic fibrosis patients and occasionally co-infect patients' lungs. Both organisms possess quorum-sensing systems dependent on N-acyl homoserine lactone (N-acyl-HSL). Cross-feeding assays demonstrated that P. aeruginosa and B. cepacia were able to utilize heterologous N-acyl-HSL signaling molecules. The ability of quorum-sensing genes from one species to complement the respective quorum-sensing mutations in the heterologous species was also examined. These studies suggest that B. cepacia CepR can use N-acyl-HSLs synthesized by RhlI and LasI and that P. aeruginosa LasR and RhlR can use N-acyl-HSLs synthesized by CepI. It is possible that a mixed bacterial population of B. cepacia and P. aeruginosa can coordinately regulate some of their virulence factors and influence the progression of lung disease due to infection with these organisms.