Impact of nutritional stress on drug susceptibility and biofilm structures of Burkholderia pseudomallei and Burkholderia thailandensis grown in static and microfluidic systems

d-Methionine-induced DNases disperse established Burkholderia pseudomallei biofilms and promotes ceftazidime susceptibility

Burkholderia pseudomallei biofilm is correlated with pathogenesis, antibiotic resistance, and relapsing cases of melioidosis, leading to challenges in clinical management. There is increasing interest in employing biofilm dispersal agents as adjunctive treatments for biofilm-associated infections. Methionine (Met) has shown promise as an anti-biofilm agent by inducing bacterial DNase production, resulting in the degradation of extracellular DNA (eDNA) and dispersion of bacterial biofilm. In this study, we investigated the impact of 0.05-50 μM D-Met and L-Met on the 24-h established biofilm of a clinical isolate, B. pseudomallei H777. Our findings revealed the ability of D-Met and L-Met to disperse the established biofilm in a non-dose-dependent manner accompanied by eDNA depletion. Real-time PCR analysis further identified an up-regulation of bacterial nuclease genes, including recJ, eddB, nth, xth, and recD, in the presence of 0.05 μM D-Met. Similarly, recJ and eddB in B. pseudomallei were up-regulated in response to the presence of 0.05 μM L-Met. Notably, D-Met enhanced the susceptibility of B. pseudomallei H777 biofilm cells to ceftazidime. Our findings indicate a correlation between methionine supplementation and the up-regulation of nuclease genes, leading to eDNA depletion and the dispersal of preformed B. pseudomallei H777 biofilm. This enhances the susceptibility of biofilm cells to ceftazidime, showing promise in combating biofilm-associated B. pseudomallei infections.

Repurposing promethazine hydrochloride to inhibit biofilm formation against Burkholderia thailandensis

Melioidosis is a severe infectious disease caused by Burkholderia pseudomallei, an intracellular pathogen with a high mortality rate and significant antibiotic resistance. The high mortality rate and resistance to antibiotics have drawn considerable attention from researchers studying melioidosis. This study evaluated the effects of various concentrations (75, 50, and 25 µg/mL) of promethazine hydrochloride (PTZ), a potent antihistamine, on biofilm formation and lipase activity after 24 h of exposure to B. thailandensis E264. A concentration-dependent decrease in both biofilm biomass and lipase activity was observed. RT-PCR analysis revealed that PTZ treatment not only made the biofilm structure loose but also reduced the expression of btaR1, btaR2, btaR3, and scmR. Single gene knockouts of quorum sensing (QS) receptor proteins (∆btaR1, ∆btaR2, and ∆btaR3) were successfully constructed. Deletion of btaR1 affected biofilm formation in B. thailandensis, while deletion of btaR2 and btaR3 led to reduced lipase activity. Molecular docking and biological performance results demonstrated that PTZ inhibits biofilm formation and lipase activity by suppressing the expression of QS-regulated genes. This study found that repositioning PTZ reduced biofilm formation in B. thailandensis E264, suggesting a potential new approach for combating melioidosis.

Biofilm Signaling, Composition and Regulation in Burkholderia pseudomallei

The incidence of melioidosis cases caused by the gram-negative pathogen Burkholderia pseudomallei (BP) is seeing an increasing trend that has spread beyond its previously known endemic regions. Biofilms produced by BP have been associated with antimicrobial therapy limitation and relapse melioidosis, thus making it urgently necessary to understand the mechanisms of biofilm formation and their role in BP biology. Microbial cells aggregate and enclose within a self-produced matrix of extracellular polymeric substances (EPSs) to form biofilm. The transition mechanism of bacterial cells from planktonic state to initiate biofilm formation, which involves the formation of surface attachment microcolonies and the maturation of the biofilm matrix, is a dynamic and complex process. Despite the emerging findings on the biofilm formation process, systemic knowledge on the molecular mechanisms of biofilm formation in BP remains fractured. This review provides insights into the signaling systems, matrix composition, and the biosynthesis regulation of EPSs (exopolysaccharide, eDNA and proteins) that facilitate the formation of biofilms in order to present an overview of our current knowledge and the questions that remain regarding BP biofilms.

DNase I and chitosan enhance efficacy of ceftazidime to eradicate Burkholderia pseudomallei biofilm cells

Biofilm-associated Burkholderia pseudomallei infection contributes to antibiotic resistance and relapse of melioidosis. Burkholderia pseudomallei biofilm matrix contains extracellular DNA (eDNA) that is crucial for biofilm establishment. However, the contribution of eDNA to antibiotic resistance by B. pseudomallei remains unclear. In this study, we first demonstrated in vitro that DNase I with the administration of ceftazidime (CAZ) at 24 h considerably inhibited the 2-day biofilm formation and reduced the number of viable biofilm cells of clinical B. pseudomallei isolates compared to biofilm treated with CAZ alone. A 3-4 log reduction in numbers of viable cells embedded in the 2-day biofilm was observed when CAZ was combined with DNase I. Confocal laser-scanning microscope visualization emphasized the competence of DNase I followed by CAZ supplementation to significantly limit B. pseudomallei biofilm development and to eradicate viable embedded B. pseudomallei biofilm cells. Furthermore, DNase I supplemented with chitosan (CS) linked with CAZ (CS/CAZ) significantly eradicated shedding planktonic and biofilm cells. These findings indicated that DNase I effectively degraded eDNA leading to biofilm inhibition and dispersion, subsequently allowing CAZ and CS/CAZ to eradicate both shedding planktonic and embedded biofilm cells. These findings provide efficient strategies to interrupt biofilm formation and improve antibiotic susceptibility of biofilm-associated infections.

Assessment of Resistance in <i>Burkholderia pseudomallei</i> to Benzalkonium Chloride and Antibiotics

The aim of the study was to investigate the features of resistance formation in Burkholderia pseudomallei to quaternary ammonium compounds, as well as to analyze its influence on the development of antibiotic resistance.

Materials and methods. 10 strains of melioidosis causative agent with typical cultural and morphological properties have been studied. The selection of variants resistant to benzalkonium chloride was carried out by successive passages on a dense nutrient medium with the addition of a disinfectant in increasing concentrations. The determination of sensitivity to benzalkonium chloride was performed through serial dilutions in agar, to antibacterial drugs from the groups of sulfonamides, β-lactams and tetracyclines – using disk diffusion method. Statistical processing of the obtained results was conducted with the help of the Microsoft Excel 2019 software. Arithmetic mean values and errors of mean values were calculated. The significance of differences between the parameters was determined applying Student’s t-test.

Results and discussion. All parental strains showed a similar degree of resistance to the disinfectant compound and most of the strains – susceptibility to the antibiotics tested. Cultivation of B. pseudomallei strains on a nutrient medium with the addition of benzalkonium chloride led to an increase in resistance to this disinfectant. In addition, an increase in the level of resistance to all studied antibiotics was found. Statistical processing of the data collected revealed a significant correlation between the change in sensitivity to benzalkonium chloride and the emergence of resistance to amoxicillin/ clavulanic acid and ceftazidime. It was found that the causative agent of melioidosis, with a natural high susceptibility to benzalkonium chloride, has a high potential for developing resistance to this disinfectant compound, which is of practical importance in the development of disinfection regimens using quarternary ammonium compounds. For the first time, a direct correlation between a decrease in the sensitivity to benzalkonium chloride in B. pseudomallei and emergence of resistance to amoxicillin/clavulonic acid and ceftazidime has been demonstrated.

Bioremediation on a chip: A portable microfluidic device for efficient screening of bacterial biofilm with polycyclic aromatic hydrocarbon removal capacity

Polycyclic aromatic hydrocarbons (PAHs) are pollutants of critical environmental and public health concern and their elimination from contaminated sites is significant for the environment. Biodegradation studies have demonstrated the ability of bacteria in biofilm conformation to enhance the biodegradation of pollutants. In this study, we used our newly developed microfluidic platform to explore biofilm development, properties, and applications of fluid flow, as a new technique for screening PAHs-degrading biofilms. The optimization and evaluation of the flow condition in the microchannels were performed through computational fluid dynamics (CFD). The formation of biofilms by PAHs-degrading bacteria Pseudomonas sp. P26 and Gordonia sp. H19, as pure cultures and co-culture, was obtained in the developed microchips. The removal efficiencies of acenaphthene, fluoranthene and pyrene were determined by HPLC. All the biofilms formed in the microchips removed all tested PAHs, with the higher removal percentages observed with the Pseudomonas sp. P26 biofilm (57.4% of acenaphthene, 40.9% of fluoranthene, and 28.9% of pyrene). Pseudomonas sp. P26 biofilm removed these compounds more efficiently than planktonic cultures. This work proved that the conformation of biofilms enhances the removal rate. It also provided a new tool to rapid and low-cost screen for effective pollutant-degrading biofilms.

Filamentous morphology of bacterial pathogens: regulatory factors and control strategies

Several studies have demonstrated that when exposed to physical, chemical, and biological stresses in the environment, many bacteria (Gram-positive and Gram-negative) change their morphology from a normal cell to a filamentous shape. The formation of filamentous morphology is one of the survival strategies against environmental stress and protection against phagocytosis or protist predators. Numerous pathogenic bacteria have shown filamentous morphologies when examined in vivo or in vitro. During infection, certain pathogenic bacteria adopt a filamentous shape inside the cell to avoid phagocytosis by immune cells. Filamentous morphology has also been seen in biofilms formed on biotic or abiotic surfaces by certain bacteria. As a result, in addition to protecting against phagocytosis by immune cells or predators, the filamentous shape aids in biofilm adhesion or colonization to biotic or abiotic surfaces. Furthermore, these filamentous morphologies of bacterial pathogens lead to antimicrobial drug resistance. Clinically, filamentous morphology has become one of the most serious challenges in treating bacterial infection. The current review went into great detail about the various factors involved in the change of filamentous morphology and the underlying mechanisms. In addition, the review discussed a control strategy for suppressing filamentous morphology in order to combat bacterial infections. Understanding the mechanism underlying the filamentous morphology induced by various environmental conditions will aid in drug development and lessen the virulence of bacterial pathogens. KEY POINTS: • The bacterial filamentation morphology is one of the survival mechanisms against several environmental stress conditions and protection from phagocytosis by host cells and protist predators. • The filamentous morphologies in bacterial pathogens contribute to enhanced biofilm formation, which develops resistance properties against antimicrobial drugs. • Filamentous morphology has become one of the major hurdles in treating bacterial infection, hence controlling strategies employed for inhibiting the filamentation morphology from combating bacterial infections.

Biofilm-mediated bioremediation is a powerful tool for the removal of environmental pollutants

Biofilm-mediated bioremediation is an attractive approach for the elimination of environmental pollutants, because of its wide adaptability, biomass, and excellent capacity to absorb, immobilize, or degrade contaminants. Biofilms are assemblages of individual or mixed microbial cells adhering to a living or non-living surface in an aqueous environment. Biofilm-forming microorganisms have excellent survival under exposure to harsh environmental stressors, can compete for nutrients, exhibit greater tolerance to pollutants compared to free-floating planktonic cells, and provide a protective environment for cells. Biofilm communities are thus capable of sorption and metabolization of organic pollutants and heavy metals through a well-controlled expression pattern of genes governed by quorum sensing. The involvement of quorum sensing and chemotaxis in biofilms can enhance the bioremediation kinetics with the help of signaling molecules, the transfer of genetic material, and metabolites. This review provides in-depth knowledge of the process of biofilm formation in microorganisms, their regulatory mechanisms of interaction, and their importance and application as powerful bioremediation agents in the biodegradation of environmental pollutants, including hydrocarbons, pesticides, and heavy metals.

New dynamic microreactor system to mimic biofilm formation and test anti-biofilm activity of nanoparticles

Microbial biofilms are composed of surface-adhered microorganisms enclosed in extracellular polymeric substances. The biofilm lifestyle is the intrinsic drug resistance imparted to bacterial cells protected by the matrix. So far, conventional drug susceptibility tests for biofilm are reagent and time-consuming, and most of them are in static conditions. Rapid and easy-to-use methods for biofilm formation and antibiotic activity testing need to be developed to accelerate the discovery of new antibiofilm strategies. Herein, a Lab-On-Chip (LOC) device is presented that provides optimal microenvironmental conditions closely mimicking real-life clinical biofilm status. This new device allows homogeneous attachment and immobilization of Pseudomonas aeruginosa PA01-EGFP cells, and the biofilms grown can be monitored by fluorescence microscopy. P. aeruginosa is an opportunistic pathogen known as a model for drug screening biofilm studies. The influence of flow rates on biofilms growth was analyzed by flow simulations using COMSOL® 5.2. Significant cell adhesion to the substrate and biofilm formation inside the microchannels were observed at higher flow rates > 100 µL/h. After biofilm formation, the effectiveness of silver nanoparticles (SNP), chitosan nanoparticles (CNP), and a complex of chitosan-coated silver nanoparticles (CSNP) to eradicate the biofilm under a continuous flow was explored. The most significant loss of biofilm was seen with CSNP with a 65.5% decrease in average live/dead cell signal in biofilm compared to the negative controls. Our results demonstrate that this system is a user-friendly tool for antibiofilm drug screening that could be simply applied in clinical laboratories.Key Points• A continuous-flow microreactor that mimics real-life clinical biofilm infections was developed.• The antibiofilm activity of three nano drugs was evaluated in dynamic conditions.• The highest biofilm reduction was observed with chitosan-silver nanoparticles.

Chitosan biological molecule improves bactericidal competence of ceftazidime against Burkholderia pseudomallei biofilms

Biofilm-associated Burkholderia pseudomallei infections (melioidosis) are problematic because of reduced sensitivity to antibiotics and high frequency of relapse. Biofilm dispersal agents are essential to liberate the biofilm-encased cells, which then become planktonic and are more susceptible to antibiotics. This study aimed to evaluate the ability of deacetylated chitosan (dCS), an antimicrobial and antibiofilm biological macromolecule, to disrupt established biofilms, thus enabling ceftazidime (CAZ) to kill biofilm-embedded B. pseudomallei. We combined dCS with CAZ using a mechanical stirring method to generate dCS/CAZ. In combination, 1.25-2.5 mg ml^-1 dCS/1-2 μg ml^-1 CAZ acted synergistically to kill cells more effectively than did either dCS or CAZ alone. Notably, a combination of 5-10 mg ml^-1 dCS with 256-512 μg ml^-1 CAZ, prepared either by mechanical stirring (dCS/CAZ) or mixing (dCS + CAZ), drastically improved bactericidal activities against biofilm cells leading to a 3-6 log CFU reduction. Confocal laser-scanning microscope (CLSM) images revealed that 10 mg ml^-1 dCS/512 μg ml^-1 CAZ is by far the best formulation to diminish B. pseudomallei biofilm biomass and produces the lowest live/dead cell ratios of B. pseudomallei in biofilm matrix. Collectively, these findings emphasize the potential of novel therapeutic antibacterial and antibiofilm agents to fight against antibiotic-tolerant B. pseudomallei biofilm-associated infections.

Predicting toxins found in toxin-antitoxin systems with a role in host-induced Burkholderia pseudomallei persistence

Burkholderia pseudomallei (Bpm) is a bacterial pathogen that causes Melioidosis, a disease with up to 40% mortality and an infection relapse of 15-23% despite antibiotic treatment. Ineffective clearance of Bpm by antibiotics is believed to be due to persistence, a hibernation-like survival mechanism modulated, in part, by toxin-antitoxin systems (TAS). Several organisms possess a repertoire of TASs but defining environmental cues eliciting their activity is hindered by laborious in vitro experiments, especially when there are many toxins with redundant function. Here, we identified which of 103 proteins in Bpm that share features found in toxins of the TAS and repurposed transcriptional data to identify which ones play a role in surviving intracellular host defenses. Putative toxins with the strongest transcriptional response were found to have low conservation between Bpm strains, while toxins that were constitutively expressed were highly conserved. Further examination of highly conserved toxins BPSS0899, BPSS1321, and BPSL1494 showed that they were functional, and their mutation led to reduce survival within macrophages and reduced in vivo persistence-associated pathology (abscesses) during treatment, but did not affect macrophages persistence. These findings highlight the utility of a data-driven approach to select putative toxins and suggests a selective role for some TAS in host survival.

Structuring biofilm communities living in pesticide contaminated water

The wide use of pesticides in agriculture expose microbiota to stressful conditions that require the development of survival strategies. The bacterial response to many pollutants has not been elucidated in detail, as well as the evolutionary processes that occur to build adapted communities. The purpose of this study was to evaluate the bacterial population structure and adaptation strategies in planktonic and biofilm communities in limited environments, as tanks containing water used for washing herbicide containers. This biodiversity, with high percentage of nonculturable microorganisms, was characterized based on habitat and abiotic parameters using molecular and bioinformatics tools. According to water and wastewater standards, the physicochemical conditions of the tank water were inadequate for survival of the identified bacteria, which had to develop survival strategies in this hostile environment. The biodiversity decreased in the transition from planktonic to biofilm samples, indicating a possible association between genetic drift and selection of individuals that survive under stressful conditions, such as heating in water and the presence of chlorine, fluorine and agrochemicals over a six-month period. The abundance of Enterobacter, Acinetobacter and Pseudomonas in biofilms from water tanks was linked to essential processes, deduced from the genes attributed to these taxonomic units, and related to biofilm formation, structure and membrane transport, quorum sensing and xenobiotic degradation. These characteristics were randomly combined and fixed in the biofilm community. Thus, communities of biofilm bacteria obtained under these environmental conditions serve as interesting models for studying herbicide biodegradation kinetics and the prospects of consortia suitable for use in bioremediation in reservoirs containing herbicide-contaminated wastewater, as biofilters containing biofilm communities capable of degrading herbicides.

Nutrient Level Determines Biofilm Characteristics and Subsequent Impact on Microbial Corrosion and Biocide Effectiveness

The impact that nutrient level has on biofilm characteristics, biocide effectiveness, and the associated risk of microbiologically influenced corrosion (MIC) was assessed using multispecies biofilms from two different oilfield consortia. A range of microbiological, microscopy, and corrosion methods demonstrated that the continuous flow of nutrients for the microbial growth resulted in higher activity, thickness, and robustness of the biofilms formed on carbon steel, which induced greater localized corrosion compared to biofilms formed under batch, nutrient-depleted conditions. Despite of the differences in biofilm characteristics, biofilms displayed comparable susceptibilities to glutaraldehyde biocide, with similar log10 reductions and percent reductions of microorganisms under both nutrient conditions. Nevertheless, nutrient replenishment impacted the effectiveness of the biocide in controlling microbial populations; a higher concentration of cells survived the biocide treatment in biofilms formed under a continuous flow of nutrients. Complementary DNA-/RNA-based amplicon sequencing and bioinformatics analysis were used to discriminate the active within the total populations in biofilms established at the different nutrient conditions and allowed the identification of the microbial species that remained active despite nutrient depletion and biocide treatment. Detection of persistent active microorganisms after exposure to glutaraldehyde, regardless of biofilm structure, suggested the presence of microorganisms less susceptible to this biocide and highlighted the importance of monitoring active microbial species for the early detection of biocide resistance in oil production facilities.IMPORTANCE Microbiologically influenced corrosion (MIC) is a complex process that generates economic losses to the industry every year. Corrosion must be managed to prevent a loss of containment of produced fluids to the external environment. MIC management includes the identification of assets with higher MIC risk, which could be influenced by nutrient levels in the system. Assessing biofilms under different nutrient conditions is essential for understanding the impact of flow regime on microbial communities and the subsequent impact on microbial corrosion and on the effectiveness of biocide treatment. This investigation simulates closely oil production systems, which contain piping sections exposed to continuous flow and sections that remain stagnant for long periods. Therefore, the results reported here are useful for MIC management and prevention. Moreover, the complementary methodological approach applied in this investigation highlighted the importance of implementing RNA-based methods for better identification of active microorganisms that survive stress conditions in oil systems.

Effects of biotic and abiotic factors on biofilm growth dynamics and their heterogeneous response to antibiotic challenge

Over the last couple of decades, with the crisis of new antimicrobial arsenal, multidrug-resistant clinical pathogens have been observed extensively. In clinical and medical settings, these persistent pathogens predominantly grow as complex heterogeneous structures enmeshed in a self-produced exopolysaccharide matrix, termed as biofilms. Since biofilms can rapidly form by adapting new environmental surroundings and have potential effect on human health, it is critical to study them promptly and consistently. Biofilm infections are challenging in the contamination of medical devices and implantations, food processing and pharmaceutical industrial settings, and in dental area caries, periodontitis and so on. The persistence of infections associated with biofilms has been mainly attributed to the increased antibiotic resistance offered by the cells growing in biofilms. In fact, it is well known that this recalcitrance of bacterial biofilms is multifactorial, and there are several resistance mechanisms that may act in parallel in order to provide an enhanced level of resistance to the biofilm. In combination, distinct resistance mechanisms significantly decrease our ability to control and eradicate biofilm-associated infections with current antimicrobial arsenal. In addition, various factors are known to influence the process of biofilm formation, growth dynamics, and their heterogeneous response towards antibiotic therapy. The current review discusses the contribution of cellular and physiochemical factors on the growth dynamics of biofilm, especially their role in antibiotic resistance mechanisms of bacterial population living in surface attached growth mode. A systematic investigation on the effects and treatment of biofilms may pave the way for novel therapeutic strategies to prevent and treat biofilms in healthcare and industrial settings.

Extracellular DNA facilitates bacterial adhesion during Burkholderia pseudomallei biofilm formation

The biofilm-forming ability of Burkholderia pseudomallei is crucial for its survival in unsuitable environments and is correlated with antibiotic resistance and relapsing cases of melioidosis. Extracellular DNA (eDNA) is an essential component for biofilm development and maturation in many bacteria. The aim of this study was to investigate the eDNA released by B. pseudomallei during biofilm formation using DNase treatment. The extent of biofilm formation and quantity of eDNA were assessed by crystal-violet staining and fluorescent dye-based quantification, respectively, and visualized by confocal laser scanning microscopy (CLSM). Variation in B. pseudomallei biofilm formation and eDNA quantity was demonstrated among isolates. CLSM images of biofilms stained with FITC-ConA (biofilm) and TOTO-3 (eDNA) revealed the localization of eDNA in the biofilm matrix. A positive correlation of biofilm biomass with quantity of eDNA during the 2-day biofilm-formation observation period was found. The increasing eDNA quantity over time, despite constant living/dead ratios of bacterial cells during the experiment suggests that eDNA is delivered from living bacterial cells. CLSM images demonstrated that depletion of eDNA by DNase I significantly lessened bacterial attachment (if DNase added at 0 h) and biofilm developing stages (if added at 24 h) but had no effect on mature biofilm (if added at 45 h). Collectively, our results reveal that eDNA is released from living B. pseudomallei and is correlated with biofilm formation. It was also apparent that eDNA is essential during bacterial cell attachment and biofilm-forming steps. The depletion of eDNA by DNase may provide an option for the prevention or dispersal of B. pseudomallei biofilm.