ccdC Regulates Biofilm Dispersal in Bacillus velezensis FZB42.

Bacillus velezensis FZB42 is a plant growth-promoting rhizobacterium (PGPR) and a model microorganism for biofilm studies. Biofilms are required for the colonization and promotion of plant growth in the rhizosphere. However, little is known about how the final stage of the biofilm life cycle is regulated, when cells regain their motility and escape the mature biofilm to spread and colonize new niches. In this study, the non-annotated gene ccdC was found to be involved in the process of biofilm dispersion. We found that the ccdC-deficient strain maintained a wrinkled state at the late stage of biofilm formation in the liquid-gas interface culture, and the bottom solution showed a clear state, indicating that no bacterial cells actively escaped, which was further evidenced by the formation of a cellular ring (biofilm pellicle) located on top of the preformed biofilm. It can be concluded that dispersal, a biofilm property that relies on motility proficiency, is also positively affected by the unannotated gene ccdC. Furthermore, we found that the level of cyclic diguanylate (c-di-GMP) in the ccdC-deficient strain was significantly greater than that in the wild-type strain, suggesting that B. velezensis exhibits a similar mechanism by regulating the level of c-di-GMP, the master regulator of biofilm formation, dispersal, and cell motility, which controls the fitness of biofilms in Pseudomonas aeruginosain. In this study, we investigated the mechanism regulating biofilm dispersion in PGPR.

Cellulase Promotes Mycobacterial Biofilm Dispersal in Response to a Decrease in the Bacterial Metabolite Gamma-Aminobutyric Acid.

Biofilm dispersal contributes to bacterial spread and disease transmission. However, its exact mechanism, especially that in the pathogen Mycobacterium tuberculosis, is unclear. In this study, the cellulase activity of the M. tuberculosis Rv0062 protein was characterized, and its effect on mycobacterial biofilm dispersal was analyzed by observation of the structure and components of Rv0062-treated biofilm in vitro. Meanwhile, the metabolite factors that induced cellulase-related biofilm dispersal were also explored with metabolome analysis and further validations. The results showed that Rv0062 protein had a cellulase activity with a similar optimum pH (6.0) and lower optimum temperature (30 °C) compared to the cellulases from other bacteria. It promoted mycobacterial biofilm dispersal by hydrolyzing cellulose, the main component of extracellular polymeric substrates of mycobacterial biofilm. A metabolome analysis revealed that 107 metabolites were significantly altered at different stages of M. smegmatis biofilm development. Among them, a decrease in gamma-aminobutyric acid (GABA) promoted cellulase-related biofilm dispersal, and this effect was realized with the down-regulation of the bacterial signal molecule c-di-GMP. All these findings suggested that cellulase promotes mycobacterial biofilm dispersal and that this process is closely associated with biofilm metabolite alterations.

Identification of signaling pathways, matrix-digestion enzymes, and motility components controlling Vibrio cholerae biofilm dispersal.

Bacteria alternate between being free-swimming and existing as members of sessile multicellular communities called biofilms. The biofilm lifecycle occurs in three stages: cell attachment, biofilm maturation, and biofilm dispersal. Vibrio cholerae biofilms are hyperinfectious, and biofilm formation and dispersal are considered central to disease transmission. While biofilm formation is well studied, almost nothing is known about biofilm dispersal. Here, we conducted an imaging screen for V. cholerae mutants that fail to disperse, revealing three classes of dispersal components: signal transduction proteins, matrix-degradation enzymes, and motility factors. Signaling proteins dominated the screen and among them, we focused on an uncharacterized two-component sensory system that we term DbfS/DbfR for dispersal of biofilm sensor/regulator. Phospho-DbfR represses biofilm dispersal. DbfS dephosphorylates and thereby inactivates DbfR, which permits dispersal. Matrix degradation requires two enzymes: LapG, which cleaves adhesins, and RbmB, which digests matrix polysaccharides. Reorientation in swimming direction, mediated by CheY3, is necessary for cells to escape from the porous biofilm matrix. We suggest that these components act sequentially: signaling launches dispersal by terminating matrix production and triggering matrix digestion, and subsequent cell motility permits escape from biofilms. This study lays the groundwork for interventions aimed at modulating V. cholerae biofilm dispersal to ameliorate disease.

Anionic amino acids support hydrolysis of poly-ß-(1,6)-N-acetylglucosamine exopolysaccharides by the biofilm dispersing glycosidase Dispersin B.

The exopolysaccharide poly-ß-(1→6)-N-acetylglucosamine (PNAG) is a major structural determinant of bacterial biofilms responsible for persistent and nosocomial infections. The enzymatic dispersal of biofilms by PNAG-hydrolyzing glycosidase enzymes, such as Dispersin B (DspB), is a possible approach to treat biofilm-dependent bacterial infections. The cationic charge resulting from partial de-N-acetylation of native PNAG is critical for PNAG-dependent biofilm formation. We recently demonstrated that DspB has increased catalytic activity on de-N-acetylated PNAG oligosaccharides, but the molecular basis for this increased activity is not known. Here, we analyze the role of anionic amino acids surrounding the catalytic pocket of DspB in PNAG substrate recognition and hydrolysis using a combination of site-directed mutagenesis, activity measurements using synthetic PNAG oligosaccharide analogs, and in vitro biofilm dispersal assays. The results of these studies support a model in which bound PNAG is weakly associated with a shallow anionic groove on the DspB protein surface with recognition driven by interactions with the -1 GlcNAc residue in the catalytic pocket. An increased rate of hydrolysis for cationic PNAG was driven, in part, by interaction with D147 on the anionic surface. Moreover, we identified that a DspB mutant with improved hydrolysis of fully acetylated PNAG oligosaccharides correlates with improved in vitro dispersal of PNAG-dependent Staphylococcus epidermidis biofilms. These results provide insight into the mechanism of substrate recognition by DspB and suggest a method to improve DspB biofilm dispersal activity by mutation of the amino acids within the anionic binding surface.

Evaluation of antibiofilm potential of four-domain α-amylase from Streptomyces griseus against exopolysaccharides (EPS) of bacterial pathogens using Danio rerio.

Biofilm formation is a major issue in healthcare settings as 75% of nosocomial infection arises due to biofilm residing bacteria. Exopolysaccharides (EPS), a key component of the biofilm matrix, contribute to the persistence of cells in a complex milieu and defends greatly from exogenous stress and demolition. It has been shown to be vital for biofilm scaffold and pathogenic features. The present study was aimed to investigate the effectiveness of four domain-containing α-amylase from Streptomyces griseus (SGAmy) in disrupting the EPS of multidrug-resistant bacteria, especially methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa. In vitro analysis of preformed biofilm unveiled the antibiofilm efficacy of SGAmy against MRSA (85%, p < 0.05) and P. aeruginosa (82%, p < 0.05). The total carbohydrate content in the EPS matrix of MRSA and P. aeruginosa was significantly reduced to 71.75% (p < 0.01) and 74.09% (p < 0.01), respectively. The findings inferred from in vitro analysis were further corroborated through in vivo studies using an experimental model organism, Danio rerio. Remarkably, the survival rate was extended to 88.8% (p < 0.05) and 74.2% (p < 0.05) in MRSA and P. aeruginosa infected fishes, respectively. An examination of gills, kidneys, and intestines of D. rerio organs depicted the reduced level of microbial colonization in SGAmy-treated cohorts and these findings were congruent with bacterial enumeration results.

Multifunctional fluorescent probes for high-throughput characterization of hexosaminidase enzyme activity.

Microbial polysaccharides composed of N-acetylglucosamine (GlcNAc), such as chitin, peptidoglycan and poly-ß-(1 â†’ 6)-GlcNAc (dPNAG), play a critical role in maintaining cell integrity or in facilitating biofilm formation in numerous fungal and bacterial pathogens. Glycosyl hydrolase enzymes that catalyze the degradation of these ß-GlcNAc containing polysaccharides play important roles in normal microbial cell physiology and can also be exploited as biocatalysts with applications as anti-fungal, anti-bacterial, or biofilm dispersal agents. Assays to rapidly detect and characterize the activity of such glycosyl hydrolase enzymes can facilitate their development as biocatalyst, however, currently available probes such as 4-methylumbelliferyl-ß-GlcNAc (4MU-GlcNAc) are not universally accepted as substrates, and their fluorescent signal is sensitive to changes in pH. Here, we present the development of a new multifunctional fluorescent substrate analog for the detection and characterization of hexosaminidase enzyme activity containing a 7-amino-4-methyl coumarin (AMC) carbamate aglycone. This probe is widely tolerated as a substrate for exo-acting ß-hexosaminidase, family 19 endo-chitinase, and the dPNAG hydrolase enzyme Dispersin B (DspB) and enables detection of hexosaminidase enzyme activity via either single wavelength fluorescent measurements or ratiometric fluorescent detection. We demonstrate the utility of this probe to screen for recombinant DspB activity in Escherichia coli cell lysates, and for the development of a high-throughput assay to screen for DspB inhibitors.

Induction of Native c-di-GMP Phosphodiesterases Leads to Dispersal of Pseudomonas aeruginosa Biofilms.

A decade of research has shown that the molecule c-di-GMP functions as a central second messenger in many bacteria. A high level of c-di-GMP is associated with biofilm formation, whereas a low level of c-di-GMP is associated with a planktonic single-cell bacterial lifestyle. c-di-GMP is formed by diguanylate cyclases and is degraded by specific phosphodiesterases. We previously presented evidence that the ectopic expression of the Escherichia coli phosphodiesterase YhjH in Pseudomonas aeruginosa results in biofilm dispersal. More recently, however, evidence has been presented that the induction of native c-di-GMP phosphodiesterases does not lead to a dispersal of P. aeruginosa biofilms. The latter result may discourage attempts to use c-di-GMP signaling as a target for the development of antibiofilm drugs. However, here, we demonstrate that the induction of the P. aeruginosa c-di-GMP phosphodiesterases PA2133 and BifA indeed results in the dispersal of P. aeruginosa biofilms in both a microtiter tray biofilm assay and a flow cell biofilm system.

Antibacterial and anti-biofilm activities of paeonol against Klebsiella pneumoniae and Enterobacter cloacae.

Paeonol, the active ingredient of Paeonia lactiflora root bark, is widely used in traditional Chinese medicine. Few studies have reported the antibacterial activity of paeonol against bacterial pathogens. In this study, the antibacterial and anti-biofilm performance of paeonol against Klebsiella pneumoniae and Enterobacter cloacae was investigated as well as its mechanisms of action. Paeonol effectively inhibited the growth of K. pneumoniae and E. cloacae with a minimum inhibitory concentration of 64 µg ml-1 and it was shown to disrupt the integrity of bacterial cell membranes, and alter cell morphology. Moreover, paeonol exhibited a potent inhibitory effect against adhesion and biofilm formation by K. pneumoniae and E. cloacae. In particular, paeonol efficiently compromised cells within biofilms, and dispersed mature biofilms. Therefore, the present study suggests that paeonol is a promising alternative antibacterial and anti-biofilm agent for combating infections caused by planktonic and biofilm cells of K. pneumoniae and E. cloacae.

In vivo model of Propionibacterium (Cutibacterium) spp. biofilm in Drosophila melanogaster.

OBJECTIVES: Acne vulgaris is a common inflammatory disorder of the pilosebaceous unit and Propionibacterium acnes biofilm-forming ability is believed to be a contributing factor to the disease development. In vivo models mimicking hair follicle environment are lacking. The aim of this study was to develop an in vivo Propionibacterium spp. biofilm model in Drosophila melanogaster (fruit fly). METHODS: We created a sterile line of D. melanogaster able to sustain Propionibacterium spp. biofilms in the gut. In order to mimic the lipid-rich, anaerobic environment of the hair follicle, fruit flies were maintained on lipid-rich diet. Propionibacterium spp. biofilms were visualized by immunofluorescence and scanning electron microscopy. We further tested if the biofilm-dispersal activity of DNase I can be demonstrated in the developed model. RESULTS: We have demonstrated the feasibility of our in vivo model for development and study of P. acnes, P. granulosum and P. avidum biofilms. The model is suitable to evaluate dispersal as well as other agents against P. acnes biofilm. CONCLUSIONS: We report a novel in vivo model for studying Propionibacterium spp. biofilms. The model can be suitable for both mechanistic as well as interventional studies.

Imaging Flow Cytometry to Study Biofilm-Associated Microbial Aggregates.

The aim of the research was to design an advanced analytical tool for the precise characterization of microbial aggregates from biofilms formed on food-processing surfaces. The approach combined imaging flow cytometry with a machine learning-based interpretation protocol. Biofilm samples were collected from three diagnostic points of the food-processing lines at two independent time points. The samples were investigated for the complexity of microbial aggregates and cellular metabolic activity. Thus, aggregates and singlets of biofilm-associated microbes were simultaneously examined for the percentages of active, mid-active, and nonactive (dead) cells to evaluate the physiology of the microbial cells forming the biofilm structures. The tested diagnostic points demonstrated significant differences in the complexity of microbial aggregates. The significant percentages of the bacterial aggregates were associated with the dominance of active microbial cells, e.g., 75.3% revealed for a mushroom crate. This confirmed the protective role of cellular aggregates for the survival of active microbial cells. Moreover, the approach enabled discriminating small and large aggregates of microbial cells. The developed tool provided more detailed characteristics of bacterial aggregates within a biofilm structure combined with high-throughput screening potential. The designed methodology showed the prospect of facilitating the detection of invasive biofilm forms in the food industry environment.

Regulation of Biofilm Aging and Dispersal in Bacillus subtilis by the Alternative Sigma Factor SigB.

Bacterial biofilms are important in natural settings, biotechnology, and medicine. However, regulation of biofilm development and its persistence in different niches is complex and only partially understood. One key step during the biofilm life cycle is dispersal, when motile cells abandon the mature biofilm to spread out and colonize new niches. Here, we show that in the model bacterium Bacillus subtilis the general stress transcription factor SigB is essential for halting detrimental overgrowth of mature biofilm and for triggering dispersal when nutrients become limited. Specifically, SigB-deficient biofilms were larger than wild-type biofilms but exhibited accelerated cell death, significantly greater sensitivity to different stresses, and reduced dispersal. Interestingly, the signal detected by SigB to limit biofilm growth was transduced through the RsbP-dependent metabolic arm of the SigB regulatory cascade, which in turn positively controlled expression of SinR, the master regulator of biofilm formation and cell motility. This novel SigB-SinR regulatory circuit might be important in controlling the fitness of biofilms (either beneficial or harmful) in diverse environments.IMPORTANCE Biofilms are crucial for bacterial survival, adaptation, and dissemination in natural, industrial, and medical systems. Sessile cells embedded in the self-produced extracellular matrix of the biofilm benefit from a division of labor and are protected from environmental insults. However, as the biofilm ages, cells become stressed because of overcrowding, starvation, and accumulation of waste products. How does the sessile biofilm community sense and respond to stressful conditions? Here, we show that in Bacillus subtilis, the transcription factors SigB and SinR control whether cells remain in or leave a biofilm when metabolic conditions become unfavorable. This novel SigB-SinR regulatory circuit might be important for controlling the fitness of biofilms (either beneficial or harmful) in diverse environments.

Nitroxide Functionalized Antibiotics Are Promising Eradication Agents against Staphylococcus aureus Biofilms.

Treatment of biofilm-related Staphylococcus aureus infections represents an important medical challenge worldwide, as biofilms, even those involving drug-susceptible S. aureus strains, are highly refractory to conventional antibiotic therapy. Nitroxides were recently shown to induce the dispersal of Gram-negative biofilms in vitro, but their action against Gram-positive bacterial biofilms remains unknown. Here, we demonstrate that the biofilm dispersal activity of nitroxides extends to S. aureus, a clinically important Gram-positive pathogen. Coadministration of the nitroxide CTEMPO (4-carboxy-2,2,6,6-tetramethylpiperidin-1-yloxyl) with ciprofloxacin significantly improved the biofilm eradication activity of the antibiotic against S. aureus Moreover, covalently linking the nitroxide to the antibiotic moiety further reduced the ciprofloxacin minimal biofilm eradication concentration. Microscopy analysis revealed that fluorescent nitroxide-antibiotic hybrids could penetrate S. aureus biofilms and enter cells localized at the surface and base of the biofilm structure. No toxicity to human cells was observed for the nitroxide CTEMPO or the nitroxide-antibiotic hybrids. Taken together, our results show that nitroxides can mediate the dispersal of Gram-positive biofilms and that dual-acting biofilm eradication antibiotics may provide broad-spectrum therapies for the treatment of biofilm-related infections.

Nitric Oxide and Iron Signaling Cues Have Opposing Effects on Biofilm Development in Pseudomonas aeruginosa.

While both iron and nitric oxide (NO) are redox-active environmental signals shown to regulate biofilm development, their interaction and roles in regulating biofilms have not been fully elucidated. In this study, exposure of Pseudomonas aeruginosa biofilms to exogenous NO inhibited the expression of iron acquisition-related genes and the production of the siderophore pyoverdine. Furthermore, supplementation of the culture medium with high levels of iron (100 µM) counteracted NO-induced biofilm dispersal by promoting the rapid attachment of planktonic cells. In the presence of iron, biofilms were found to disperse transiently to NO, while the freshly dispersed cells reattached rapidly within 15 min. This effect was not due to the scavenging of NO by free iron but involved a cellular response induced by iron that led to the elevated production of the exopolysaccharide Psl. Interestingly, most Psl remained on the substratum after treatment with NO, suggesting that dispersal involved changes in the interactions between Psl and P. aeruginosa cells. Taken together, our results suggest that iron and NO regulate biofilm development via different pathways, both of which include the regulation of Psl-mediated attachment. Moreover, the addition of an iron chelator worked synergistically with NO in the dispersal of biofilms.IMPORTANCE Nitric oxide (NO), which induces biofilm dispersal, is a promising strategy for biofilm control in both clinical and industrial contexts. However, competing environmental signals may reduce the efficacy of NO. The results presented here suggest that the presence of iron represents one such environmental cue that antagonizes the activity of NO as a biofilm-dispersing agent. Based on this understanding, we developed a strategy to enhance dispersal by combining NO with an iron-scavenging agent. Overall, this study links two important environmental signals, iron and NO, with their roles in biofilm development and suggests new ways for improving the use of NO in biofilm control strategies.

Living biofouling-resistant membranes as a model for the beneficial use of engineered biofilms.

Membrane systems are used increasingly for water treatment, recycling water from wastewater, during food processing, and energy production. They thus are a key technology to ensure water, energy, and food sustainability. However, biofouling, the build-up of microbes and their polymeric matrix, clogs these systems and reduces their efficiency. Realizing that a microbial film is inevitable, we engineered a beneficial biofilm that prevents membrane biofouling, limiting its own thickness by sensing the number of its cells that are present via a quorum-sensing circuit. The beneficial biofilm also prevents biofilm formation by deleterious bacteria by secreting nitric oxide, a general biofilm dispersal agent, as demonstrated by both short-term dead-end filtration and long-term cross-flow filtration tests. In addition, the beneficial biofilm was engineered to produce an epoxide hydrolase so that it efficiently removes the environmental pollutant epichlorohydrin. Thus, we have created a living biofouling-resistant membrane system that simultaneously reduces biofouling and provides a platform for biodegradation of persistent organic pollutants.

A potential substrate binding pocket of BdcA plays a critical role in NADPH recognition and biofilm dispersal.

Biofilm dispersal is characterized by the cell detachment from biofilms and expected to provide novel "anti-biofilm" approaches of prevention and treatment of biofilms in clinical and industrial settings. The E.coli protein BdcA has been identified as a biofilm dispersal factor and designed to be an important component in engineered applications to control biofilm formation. It belongs to short-chain dehydrogenase/reductase (SDR) family with the specific affinity to NADPH. Here, we show the structure of BdcA in complex with NADPH and confirm that NADPH binding is requisite for BdcA facilitating cell motility and increasing biofilm dispersal. Especially, we observe a potential substrate binding pocket surrounded by hydrophobic residues upon NADPH binding and present evidences that this pocket is essential for BdcA binding NADPH and exerting its biological functions. Our study provides the clues for illuminating the molecular mechanism of BdcA regulating biofilm dispersal and better utilizing BdcA to eliminate the biofilms.

Automated Microscopic Analysis of Metal Sulfide Colonization by Acidophilic Microorganisms.

Industrial biomining processes are currently focused on metal sulfides and their dissolution, which is catalyzed by acidophilic iron(II)- and/or sulfur-oxidizing microorganisms. Cell attachment on metal sulfides is important for this process. Biofilm formation is necessary for seeding and persistence of the active microbial community in industrial biomining heaps and tank reactors, and it enhances metal release. In this study, we used a method for direct quantification of the mineral-attached cell population on pyrite or chalcopyrite particles in bioleaching experiments by coupling high-throughput, automated epifluorescence microscopy imaging of mineral particles with algorithms for image analysis and cell quantification, thus avoiding human bias in cell counting. The method was validated by quantifying cell attachment on pyrite and chalcopyrite surfaces with axenic cultures of Acidithiobacillus caldus, Leptospirillum ferriphilum, and Sulfobacillus thermosulfidooxidans. The method confirmed the high affinity of L. ferriphilum cells to colonize pyrite and chalcopyrite surfaces and indicated that biofilm dispersal occurs in mature pyrite batch cultures of this species. Deep neural networks were also applied to analyze biofilms of different microbial consortia. Recent analysis of the L. ferriphilum genome revealed the presence of a diffusible soluble factor (DSF) family quorum sensing system. The respective signal compounds are known as biofilm dispersal agents. Biofilm dispersal was confirmed to occur in batch cultures of L. ferriphilum and S. thermosulfidooxidans upon the addition of DSF family signal compounds.IMPORTANCE The presented method for the assessment of mineral colonization allows accurate relative comparisons of the microbial colonization of metal sulfide concentrate particles in a time-resolved manner. Quantitative assessment of the mineral colonization development is important for the compilation of improved mathematical models for metal sulfide dissolution. In addition, deep-learning algorithms proved that axenic or mixed cultures of the three species exhibited characteristic biofilm patterns and predicted the biofilm species composition. The method may be extended to the assessment of microbial colonization on other solid particles and may serve in the optimization of bioleaching processes in laboratory scale experiments with industrially relevant metal sulfide concentrates. Furthermore, the method was used to demonstrate that DSF quorum sensing signals directly influence colonization and dissolution of metal sulfides by mineral-oxidizing bacteria, such as L. ferriphilum and S. thermosulfidooxidans.

Activity of Norspermidine on Bacterial Biofilms of Multidrug-Resistant Clinical Isolates Associated with Persistent Extremity Wound Infections.

Biofilm formation is a major virulence factor for numerous pathogenic bacteria and is cited as a central event in the pathogenesis of chronic human infections, which is in large part due to excessive extracellular matrix secretion and metabolic changes that occur within the biofilm rendering them highly tolerant to antimicrobial treatments. Polyamines, including norspermidine, play central roles in bacterial biofilm development, but have also recently been shown to inhibit biofilm formation in select strains of various pathogenic bacteria. The aim of this study was to evaluate in vitro the biofilm dispersive and inhibitory activities of norspermidine against multidrug-resistant clinical isolates of Acinetobacter baumannii(n = 4), Klebsiella pneumoniae (n = 3), Pseudomonas aeruginosa (n = 5) and Staphylococcus aureus (n = 4) associated with chronic extremity wound infections using the semi-quantitative 96-well plate method and confocal laser microscopy. In addition to the antibiofilm activity, biocompatibility of norspermidine was also evaluated by measuring toxicity in vitro to human cell lines and whole porcine tissue explants using MTT viability assay and histological analysis. Norspermidine (5-20 mM) had variable dispersive and inhibitory activity on biofilms which was dependent on both the strain and species. Of the clinical bacterial species evaluated herein, A. baumannii isolates were the most sensitive to the effect of norspermidine, which was in part due to the inhibitory effects of norspermidine on bacterial motility and expression of genes involved in the production of homoserine lactones and quorum sensing molecules both essential for biofilm formation. Importantly, exposure of cell lines and whole tissues to norspermidine for prolonged periods of time (≥24 h) was observed to reduce viability and alter tissue histology in a time and concentration dependent manner, with 20 mM exposure having the greatest negative effects on both tissues and individual cell lines. Collectively our findings demonstrate that, similar to other polyamines, norspermidine displays both inhibitory and dispersive activities on biofilms of clinical multidrug-resistant bacterial isolates, in particular for strains of A. baumannii. Additionally our findings suggest that direct application may be considered on tissues, albeit for limited exposure times.

Nitric oxide-releasing polyacrylonitrile disperses biofilms formed by wound-relevant pathogenic bacteria.

AIMS: To test the antimicrobial and antibiofilm properties of a nitric oxide (NO)-releasing polymer against wound-relevant bacterial pathogens. METHODS AND RESULTS: Using a variety of 96-well plate assay systems that include standard well plates and the minimum biofilm eradication concentration biofilm assay well plate, a NO-releasing polymer based on (poly)acrylonitrile (PAN/NO) was studied for antimicrobial and antibiofilm activity against the common wound pathogens Pseudomonas aeruginosa (PAO1), Staphylococcus aureus (Mu50) and Enterococcus faecalis (V583). The polymer was capable of dispersing single-species biofilms of Ps. aeruginosa as well as a more clinically relevant multispecies biofilm that incorporates Ps. aeruginosa along with Staph. aureus and Ent. faecalis. PAN/NO also synergistically enhanced the susceptibility of the multispecies biofilms to the common broad-spectrum antibiotic, ciprofloxacin. Multiple in vitro biocompatibility assays show that PAN/NO has limited potential for mammalian cytotoxicity. CONCLUSION: This study demonstrates the feasibility of utilizing the NO-releasing polymer, PAN/NO, to manage biofilms formed by wound-relevant pathogens, and provides proof-of-concept for use of this NO-releasing polymer platform across multiple disciplines where bacterial biofilms pose significant problems. SIGNIFICANCE AND IMPACT OF STUDY: In the clinical sector, bacterial biofilms represent a substantial treatment challenge for health care professionals and are widely recognized as a key factor in prolonging patient morbidity. This study highlights the potential role for the ubiquitous signalling molecule nitric oxide (NO) as an antibiofilm therapy.

Discovery of quinoline small molecules with potent dispersal activity against methicillin-resistant Staphylococcus aureus and Staphylococcus epidermidis biofilms using a scaffold hopping strategy.

Staphylococcus aureus and Staphylococcus epidermidis are recognized as the most frequent cause of biofilm-associated nosocomial and indwelling medical device infections. Biofilm-associated infections are known to be highly resistant to our current arsenal of clinically used antibiotics and antibacterial agents. To exacerbate this problem, no therapeutic option exists that targets biofilm-dependent machinery critical to Staphylococcal biofilm formation and maintenance. Here, we describe the discovery of a series of quinoline small molecules that demonstrate potent biofilm dispersal activity against methicillin-resistant S. aureus and S. epidermidis using a scaffold hopping strategy. This interesting class of quinolines also has select synthetic analogues that demonstrate potent antibacterial activity and biofilm inhibition against S. aureus and S. epidermidis.

Biofilm formation and dispersal of Staphylococcus aureus wound isolates in microtiter plate-based 2-D wound model.

Biofilm-associated wound infections in diabetic and immunocompromised patients are an increasing threat due to rising antibiotic resistance. Various wound models have been used to screen for efficient antiinfection treatments. However, results from in vitro models do not always match in vivo results, and this represents a bottleneck for development of new infection treatments. In this study, a static 2-D microtiter plate-based biofilm model was tested for growing clinically relevant Staphylococcus aureus wound isolates in various operating conditions, seeking to identify an optimal setup that would yield physiologically relevant results. Specifically, the tested variables included wound-mimicking growth media, precoating of surface with different proteins, multiwell plates with various surface properties, and the effect of bacterial pre-attachment step. Our results indicated that protein precoating is a key factor for supporting biofilm growth. The same wound isolate responded with significant differences in biofilm formation to different wound-mimicking media. Biofilm dispersal, as a proxy for effectiveness of antibiofilm treatments, was also investigated in response to proteinase K. The dispersal effect of proteinase K showed that the biofilm dispersal is contingent upon the specific wound isolate, with isolates CCUG 35571 and ATCC 6538 showing considerable dispersal responses. In conclusion, this study observed a higher biofilm formation in isolates when a protein precoating of collagen type I was applied but being dependent on the growth media selected. That is why we recommend to use simulated wound fluid or a wound-mimicking growth media to perform similar studies. Furthermore, proteinase K is suggested as an important factor that could affect biofilm dispersal within such models, since biofilm dispersal was induced in isolates CCUG 35571 and ATCC 6538 in simulated wound fluid on precoated collagen type I plates.