Biofilm formation with mixed cultures of Pseudomonas aeruginosa/Escherichia coli on silicone using artificial urine to mimic urinary catheters

Evaluation of phenotypic and genotypic methods for the identification and characterization of bacterial isolates recovered from catheter-associated urinary tract infections

AIMS

Urinary tract infections are the most common hospital-acquired infection, 80% of which are associated with catheterization. Diagnostic methods may influence the reported identities of these pathogens, and phenotypic testing under laboratory conditions may not reflect infection phenotypes. This study aimed to evaluate the efficacy of diagnostic methods and whether medium composition alters phenotypes by characterizing catheter-associated urinary tract infection isolates from a UK hospital.

METHODS AND RESULTS

We compared five bacterial identification methods, including biochemical testing, matrix-assisted laser desorption/ionization biotyping, and genome sequencing, finding differences in genus- or species-level identifications. Antibiotic susceptibility comparisons between phenotypic assays and genomic predictions showed high agreement only in multidrug-resistant strains. To determine whether growth rate and biofilm formation were affected by medium composition, strains were grown in both planktonic and biofilm states. Low planktonic growth and significant biofilm formation were observed in artificial urine compared to rich laboratory media, underscoring the importance of assay design.

CONCLUSIONS

This study highlights the risks of relying on a single diagnostic method for species identification, advocating for whole-genome sequencing for accuracy. It emphasizes the continued importance of phenotypic methods in understanding antibiotic resistance in clinical settings and the need for characterization conditions that mirror those encountered by pathogens in the body.

Ecology of Legionella pneumophila biofilms: The link between transcriptional activity and the biphasic cycle

There has been considerable discussion regarding the environmental life cycle of Legionella pneumophila and its virulence potential in natural and man-made water systems. On the other hand, the bacterium's morphogenetic mechanisms within host cells (amoeba and macrophages) have been well documented and are linked to its ability to transition from a non-virulent, replicative state to an infectious, transmissive state. Although the morphogenetic mechanisms associated with the formation and detachment of the L. pneumophila biofilm have also been described, the capacity of the bacteria to multiply extracellularly is not generally accepted. However, several studies have shown genetic pathways within the biofilm that resemble intracellular mechanisms. Understanding the functionality of L. pneumophila cells within a biofilm is fundamental for assessing the ecology and evaluating how the biofilm architecture influences L. pneumophila survival and persistence in water systems. This manuscript provides an overview of the biphasic cycle of L. pneumophila and its implications in associated intracellular mechanisms in amoeba. It also examines the molecular pathways and gene regulation involved in L. pneumophila biofilm formation and dissemination. A holistic analysis of the transcriptional activities in L. pneumophila biofilms is provided, combining the information of intracellular mechanisms in a comprehensive outline. Furthermore, this review discusses the techniques that can be used to study the morphogenetic states of the bacteria within biofilms, at the single cell and population levels.

The use of biomimetic surfaces to reduce single- and dual-species biofilms of Escherichia coli and Pseudomonas putida

The ability of bacteria to adhere to and form biofilms on food contact surfaces poses serious challenges, as these may lead to the cross-contamination of food products. Biomimetic topographic surface modifications have been explored to enhance the antifouling performance of materials. In this study, the topography of two plant leaves, Brassica oleracea var. botrytis (cauliflower, CF) and Brassica oleracea capitate (white cabbage, WC), was replicated through wax moulding, and their antibiofilm potential was tested against single- and dual-species biofilms of Escherichia coli and Pseudomonas putida. Biomimetic surfaces exhibited higher roughness values (SaWC = 4.0 ± 1.0 μm and SaCF = 3.3 ± 1.0 μm) than the flat control (SaF = 0.6 ± 0.2 μm), whilst the CF surface demonstrated a lower interfacial free energy (ΔGiwi) than the WC surface (-100.08 mJ m-2 and -71.98 mJ m-2, respectively). The CF and WC surfaces had similar antibiofilm effects against single-species biofilms, achieving cell reductions of approximately 50% and 60% for E. coli and P. putida, respectively, compared to the control. Additionally, the biomimetic surfaces led to reductions of up to 60% in biovolume, 45% in thickness, and 60% in the surface coverage of single-species biofilms. For dual-species biofilms, only the E. coli strain growing on the WC surface exhibited a significant decrease in the cell count. However, confocal microscopy analysis revealed a 60% reduction in the total biovolume and surface coverage of mixed biofilms developed on both biomimetic surfaces. Furthermore, dual-species biofilms were mainly composed of P. putida, which reduced E. coli growth. Altogether, these results demonstrate that the surface properties of CF and WC biomimetic surfaces have the potential for reducing biofilm formation.

Dual-Species Biofilms: Biomass, Viable Cell Ratio/Cross-Species Interactions, Conjugative Transfer

Biofilms as a form of adaptation are beneficial for bacterial survival and may be hot spots for horizontal gene transfer, including conjugation. The aim of this research was to characterize the biofilm biomass, viable cell ratios and conjugative transfer of the pOX38 plasmid, an F-plasmid derivative, from the Escherichia coli N4i pOX38 strain (donor) into a uropathogenic E. coli DL82 strain (recipient) within dual-species biofilms with one of the following opportunistic pathogenic bacteria: Klebsiella pneumoniae, Enterococcus faecalis or Pseudomonas aeruginosa. Dual-species biofilms of E. coli with K. pneumoniae or P. aeruginosa but not E. faecalis were more massive and possessed more exopolysaccharide matrix compared to single-species biofilms of donor and recipient cells. Correlation between biofilm biomass and exopolysaccharide matrix was rs = 0.888 in dual-species biofilms. In dual-species biofilm with E. faecalis the proportion of E. coli was the highest, while in the biofilm with P. aeruginosa and K. pneumoniae, the E. coli was less abundant. The conjugative frequencies of plasmid transfer in dual-species biofilms of E. coli with E. faecalis and P. aeruginosa were reduced. A decrease in conjugative frequency was also observed when cell-free supernatants (CFSs) of E. faecalis and P. aeruginosa were added to the E. coli conjugation mixture. Further, the activity of the autoinducer AI-2 in the CFSs of the E. coli conjugation mixture was reduced when bacteria or CFSs of E. faecalis and P. aeruginosa were added to the E. coli conjugation mixture. Hence, the intercellular and interspecies interactions in dual-species biofilms depend on the partners involved.

Imaging biofilms using fluorescence in situ hybridization: seeing is believing

Biofilms are complex structures with an intricate relationship between the resident microorganisms, the extracellular matrix, and the surrounding environment. Interest in biofilms is growing exponentially given its ubiquity in so diverse fields such as healthcare, environmental and industry. Molecular techniques (e.g., next-generation sequencing, RNA-seq) have been used to study biofilm properties. However, these techniques disrupt the spatial structure of biofilms; therefore, they do not allow to observe the location/position of biofilm components (e.g., cells, genes, metabolites), which is particularly relevant to explore and study the interactions and functions of microorganisms. Fluorescence in situ hybridization (FISH) has been arguably the most widely used method for an in situ analysis of spatial distribution of biofilms. In this review, an overview on different FISH variants already applied on biofilm studies (e.g., CLASI-FISH, BONCAT-FISH, HiPR-FISH, seq-FISH) will be explored. In combination with confocal laser scanning microscopy, these variants emerged as a powerful approach to visualize, quantify and locate microorganisms, genes, and metabolites inside biofilms. Finally, we discuss new possible research directions for the development of robust and accurate FISH-based approaches that will allow to dig deeper into the biofilm structure and function.

Interactions of microorganisms within a urinary catheter polymicrobial biofilm model

Biofilms are often polymicrobial in nature, which can impact their behavior and overall structure, often resulting in an increase in biomass and enhanced antimicrobial resistance. Using plate counts and locked nucleic acid/2'-O-methyl-RNA fluorescence in situ hybridization (LNA/2'OMe-FISH), we studied the interactions of four species commonly associated with catheter-associated urinary tract infections (CAUTI): Enterococcus faecalis, Escherichia coli, Candida albicans, and Proteus mirabilis. Eleven combinations of biofilms were grown on silicone coupons placed in 24-well plates for 24 h, 37°C, in artificial urine medium (AUM). Results showed that P. mirabilis was the dominant species and was able to inhibit both E. coli and C. albicans growth. In the absence of P. mirabilis, an antagonistic relationship between E. coli and C. albicans was observed, with the former being dominant. E. faecalis growth was not affected in any combination, showing a more mutualistic relationship with the other species. Imaging results correlated with the plate count data and provided visual verification of species undetected using the viable plate count. Moreover, the three bacterial species showed overall good repeatability SD (S_r ) values (0.1-0.54) in all combinations tested, whereas C. albicans had higher repeatability S_r values (0.36-1.18). The study showed the complexity of early-stage interactions in polymicrobial biofilms. These interactions could serve as a starting point when considering targets for preventing or treating CAUTI biofilms containing these species.

Does Secondary Plant Metabolite Ursolic Acid Exhibit Antibacterial Activity against Uropathogenic Escherichia coli Living in Single- and Multispecies Biofilms?

Multispecies bacterial biofilms are the often cause of chronic recurrent urinary tract infections within the human population. Eradicating such a complex bacterial consortium with standard pharmacotherapy is often unsuccessful. Therefore, plant-derived compounds are currently being researched as an alternative strategy to antibiotic therapy for preventing bacterial biofilm formation and facilitating its eradication. Therefore, our research aimed to determine the effect of secondary plant metabolite ursolic acid (UA) on the growth and survival, the quantity of exopolysaccharides formed, metabolic activity, and morphology of uropathogenic Gram-negative rods living in single- and mixed-species biofilms at various stages of their development. Spectrophotometric methods were used for biofilm mass formation and metabolic activity determination. The survival of bacteria was established using the serial dilution assay. The decrease in survival and inhibition of biofilm creation, both single- and multispecies, as well as changes in the morphology of bacterial cells were noticed. As UA exhibited better activity against young biofilms, the use of UA-containing formulations, especially during the initial steps of urinary tract infection, seems to be reasonable. However, the future direction should be a thorough understanding of the mechanisms of UA activity as a bioactive substance.

Enhanced Antibiotic Tolerance of an In Vitro Multispecies Uropathogen Biofilm Model, Useful for Studies of Catheter-Associated Urinary Tract Infections

Catheter-associated urinary tract infections (CAUTI) are a common clinical concern as they can lead to severe, persistent infections or bacteremia in long-term catheterized patients. This type of CAUTI is difficult to eradicate, as they are caused by multispecies biofilms that may have reduced susceptibility to antibiotics. Many new strategies to tackle CAUTI have been proposed in the past decade, including antibiotic combination treatments, surface modification and probiotic usage. However, those strategies were mainly assessed on mono- or dual-species biofilms that hardly represent the long-term CAUTI cases where, normally, 2–4 or even more species can be involved. We developed a four-species in vitro biofilm model on catheters involving clinical strains of Escherichia coli, Pseudomonas aeruginosa, Klebsiella oxytoca and Proteus mirabilis isolated from indwelling catheters. Interspecies interactions and responses to antibiotics were quantitatively assessed. Collaborative as well as competitive interactions were found among members in our model biofilm and those interactions affected the individual species’ abundances upon exposure to antibiotics as mono-, dual- or multispecies biofilms. Our study shows complex interactions between species during the assessment of CAUTI control strategies for biofilms and highlights the necessity of evaluating treatment and control regimes in a multispecies setting.

The role of Nucleic Acid Mimics (NAMs) on FISH-based techniques and applications for microbial detection

Fluorescent in situ hybridization (FISH) is a powerful tool that for more than 30 years has allowed to detect and quantify microorganisms as well as to study their spatial distribution in three-dimensional structured environments such as biofilms. Throughout these years, FISH has been improved in order to face some of its earlier limitations and to adapt to new research objectives. One of these improvements is related to the emergence of Nucleic Acid Mimics (NAMs), which are now employed as alternatives to the DNA and RNA probes that have been classically used in FISH. NAMs such as peptide and locked nucleic acids (PNA and LNA) have provided enhanced sensitivity and specificity to the FISH technique, as well as higher flexibility in terms of applications. In this review, we aim to cover the state-of-the-art of the different NAMs and explore their possible applications in FISH, providing a general overview of the technique advancement in the last decades.

An Update on the Effectiveness of Probiotics in the Prevention and Treatment of Cancer

Probiotics are living microbes that play a significant role in protecting the host in various ways. Gut microbiota is one of the key players in maintaining homeostasis. Cancer is considered one of the most significant causes of death worldwide. Although cancer treatment has received much attention in recent years, the number of people suffering from neoplastic syndrome continues to increase. Despite notable improvements in the field of cancer therapy, tackling cancer has been challenging due to the multiple properties of cancer cells and their ability to evade the immune system. Probiotics alter the immunological and cellular responses by enhancing the epithelial barrier and stimulating the production of anti-inflammatory, antioxidant, and anticarcinogenic compounds, thereby reducing cancer burden and growth. The present review focuses on the various mechanisms underlying the role of probiotics in the prevention and treatment of cancer.

Using Lactobacilli to Fight Escherichia coli and Staphylococcus aureus Biofilms on Urinary Tract Devices

The low efficacy of conventional treatments and the interest in finding natural-based approaches to counteract biofilm development on urinary tract devices have promoted the research on probiotics. This work evaluated the ability of two probiotic strains, Lactobacillus plantarum and Lactobacillus rhamnosus, in displacing pre-formed biofilms of Escherichia coli and Staphylococcus aureus from medical-grade silicone. Single-species biofilms of 24 h were placed in contact with each probiotic suspension for 6 h and 24 h, and the reductions in biofilm cell culturability and total biomass were monitored by counting colony-forming units and crystal violet assay, respectively. Both probiotics significantly reduced the culturability of E. coli and S. aureus biofilms, mainly after 24 h of exposure, with reduction percentages of 70% and 77% for L. plantarum and 76% and 63% for L. rhamnosus, respectively. Additionally, the amount of E. coli biofilm determined by CV staining was maintained approximately constant after 6 h of probiotic contact and significantly reduced up to 67% after 24 h. For S. aureus, only L. rhamnosus caused a significant effect on biofilm amount after 6 h of treatment. Hence, this study demonstrated the potential of lactobacilli to control the development of pre-established uropathogenic biofilms.

Are Uropathogenic Bacteria Living in Multispecies Biofilm Susceptible to Active Plant Ingredient-Asiatic Acid?

Urinary tract infections (UTIs) are a serious health problem in the human population due to their chronic and recurrent nature. Bacteria causing UTIs form multispecies biofilms being resistant to the activity of the conventionally used antibiotics. Therefore, compounds of plant origin are currently being searched for, which could constitute an alternative strategy to antibiotic therapy. Our study aimed to determine the activity of asiatic acid (AA) against biofilms formed by uropathogenic Escherichia coli, Enterobacter cloacae, and Pseudomonas aeruginosa. The influence of AA on the survival, biofilm mass formation by bacteria living in mono-, dual-, and triple-species consortia as well as the metabolic activity and bacterial cell morphology were determined. The spectrophotometric methods were used for biofilm mass synthesis and metabolic activity determination. The survival of bacteria was established using the serial dilution assay. The decrease in survival and a weakening of the ability to create biofilms, both single and multi-species, as well as changes in the morphology of bacterial cells were noticed. As AA works best against young biofilms, the use of AA-containing formulations, especially during the initial stages of infection, seems to be reasonable. However, there is a need for further research concerning AA especially regarding its antibacterial mechanisms of action.

Insulin Regulation of Escherichia coli Abiotic Biofilm Formation: Effect of Nutrients and Growth Conditions

Escherichia coli plays an important role in biofilm formation across a wide array of disease and ecological settings. Insulin can function as an adjuvant in the regulation of biofilm levels. The modulation of insulin-regulated biofilm formation by environmental conditions has not been previously described. In the present study, the effects that various environmental growth conditions and nutrients have on insulin-modulated levels of biofilm production were measured. Micropipette tips were incubated with E. coli ATCC^® 25922™ in a Mueller Hinton broth (MH), or a yeast nitrogen base with 1% peptone (YNBP), which was supplemented with glucose, lactose, galactose and/or insulin (Humulin^®-R). The incubation conditions included a shaking or static culture, at 23 °C or 37 °C. After incubation, the biofilm production was calculated per CFU. At 23 °C, the presence of insulin increased biofilm formation. The amount of biofilm formation was highest in glucose > galactose >> lactose, while the biofilm levels decreased in shaking cultures, except for galactose (3-fold increase; 0.1% galactose and 20 μU insulin). At 37 °C, regardless of condition, there was more biofilm formation/CFU under static conditions in YNBP than in MH, except for the MH containing galactose. E. coli biofilm formation is influenced by aeration, temperature, and insulin concentration in combination with the available sugars.

Polymeric Nanoparticles Active against Dual-Species Bacterial Biofilms

Biofilm infections are a global public health threat, necessitating new treatment strategies. Biofilm formation also contributes to the development and spread of multidrug-resistant (MDR) bacterial strains. Biofilm-associated chronic infections typically involve colonization by more than one bacterial species. The co-existence of multiple species of bacteria in biofilms exacerbates therapeutic challenges and can render traditional antibiotics ineffective. Polymeric nanoparticles offer alternative antimicrobial approaches to antibiotics, owing to their tunable physico-chemical properties. Here, we report the efficacy of poly(oxanorborneneimide) (PONI)-based antimicrobial polymeric nanoparticles (PNPs) against multi-species bacterial biofilms. PNPs showed good dual-species biofilm penetration profiles as confirmed by confocal laser scanning microscopy. Broad-spectrum antimicrobial activity was observed, with reduction in both bacterial viability and overall biofilm mass. Further, PNPs displayed minimal fibroblast toxicity and high antimicrobial activity in an in vitro co-culture model comprising fibroblast cells and dual-species biofilms of Escherichia coli and Pseudomonas aeruginosa. This study highlights a potential clinical application of the presented polymeric platform.

Effect of Lactobacillus plantarum Biofilms on the Adhesion of Escherichia coli to Urinary Tract Devices

Novel technologies to prevent biofilm formation on urinary tract devices (UTDs) are continually being developed, with the ultimate purpose of reducing the incidence of urinary infections. Probiotics have been described as having the ability to displace adhering uropathogens and inhibit microbial adhesion to UTD materials. This work aimed to evaluate the effect of pre-established Lactobacillus plantarum biofilms on the adhesion of Escherichia coli to medical-grade silicone. The optimal growth conditions of lactobacilli biofilms on silicone were first assessed in 12-well plates. Then, biofilms of L. plantarum were placed in contact with E. coli suspensions for up to 24 h under quasi-static conditions. Biofilm monitoring was performed by determining the number of culturable cells and by confocal laser scanning microscopy (CLSM). Results showed significant reductions of 76%, 77% and 99% in E. coli culturability after exposure to L. plantarum biofilms for 3, 6 and 12 h, respectively, corroborating the CLSM analysis. The interactions between microbial cell surfaces and the silicone surface with and without L. plantarum biofilms were also characterized using contact angle measurements, where E. coli was shown to be thermodynamically less prone to adhere to L. plantarum biofilms than to silicone. Thus, this study suggests the use of probiotic cells as potential antibiofilm agents for urinary tract applications.

Biofilm-Producing Bacteria and Risk Factors (Gender and Duration of Catheterization) Characterized as Catheter-Associated Biofilm Formation

Background

A catheter-associated urinary tract infection (CA-UTI) is preceded by biofilm formation, which is related to several risk factors such as gender, age, diabetic status, duration of catheterization, bacteriuria before catheterization, virulence gene factor, and antibiotic usage.

Aims

This study aims to identify the microbial composition of catheter samples, including its corresponding comparison with urine samples, to determine the most important risk factors of biofilm formation and characterize the virulence gene factors that correlate with biofilm formation.

Methods

A longitudinal cross-sectional study was conducted on 109 catheterized patients from September 2017 to January 2018. The risk factors were obtained from the patients' medical records. All catheter and urine samples were cultured after removal, followed by biomass quantification. Isolate identification and antimicrobial susceptibility testing were performed using the Vitex2 system. Biofilm-producing bacteria were identified by the Congo Red Agar (CRA) method. A PCR test characterized the virulence genes of dominant bacteria (E. coli). All data were collected and processed for statistical analysis.

Results

Out of 109 catheterized patients, 78% of the catheters were culture positive, which was higher than those of the urine samples (37.62%). The most common species isolated from the catheter cultures were Escherichia coli (28.1%), Candida sp. (17.8%), Klebsiella pneumoniae (15.9%), and Enterococcus faecalis (13.1%). E. coli (83.3%) and E. faecalis (78.6%) were the main isolates with a positive CRA. A statistical analysis showed that gender and duration prior to catheterization were associated with an increased risk of biofilm formation (p < 0.05).

Conclusion

E. coli and E. faecalis were the most common biofilm-producing bacteria isolated from the urinary catheter. Gender and duration are two risk factors associated with biofilm formation, therefore determining the risk of CAUTI. The presence of PapC as a virulence gene encoding pili correlates with the biofilm formation. Biofilm-producing bacteria, female gender, duration of catheterization (more than five days), and PapC gene presence have strong correlation with the biofilm formation. To prevent CAUTI, patients with risk factors should be monitored by urinalysis tests to detect earlier the risk of biofilm formation.

Polymicrobial interactions in the urinary tract: is the enemy of my enemy my friend?

The vast majority of research pertaining to urinary tract infection has focused on a single pathogen in isolation, and predominantly Escherichia coli. However, polymicrobial urine colonization and infection are prevalent in several patient populations, including individuals with urinary catheters. The progression from asymptomatic colonization to symptomatic infection and severe disease is likely shaped by interactions between traditional pathogens as well as constituents of the normal urinary microbiota. Recent studies have begun to experimentally dissect the contribution of polymicrobial interactions to disease outcomes in the urinary tract, including their role in development of antimicrobial-resistant biofilm communities, modulating the innate immune response, tissue damage, and sepsis. This review aims to summarize the epidemiology of polymicrobial urine colonization, provide an overview of common urinary tract pathogens, and present key microbe-microbe and host-microbe interactions that influence infection progression, persistence, and severity.

Pseudomonas putida as a potential biocontrol agent against Salmonella Java biofilm formation in the drinking water system of broiler houses

Background

Environmental biofilms can induce attachment and protection of other microorganisms including pathogens, but can also prevent them from invasion and colonization. This opens the possibility for so-called biocontrol strategies, wherein microorganisms are applied to control the presence of other microbes. The potential for both positive and negative interactions between microbes, however, raises the need for in depth characterization of the sociobiology of candidate biocontrol agents (BCAs). The inside of the drinking water system (DWS) of broiler houses is an interesting niche to apply BCAs, because contamination of these systems with pathogens plays an important role in the infection of broiler chickens and consequently humans. In this study, Pseudomonas putida, which is part of the natural microbiota in the DWS of broiler houses, was evaluated as BCA against the broiler pathogen Salmonella Java.

Results

To study the interaction between these species, an in vitro model was developed simulating biofilm formation in the drinking water system of broilers. Dual-species biofilms of P. putida strains P1, P2, and P3 with S. Java were characterized by competitive interactions, independent of P. putida strain, S. Java inoculum density and application order. When equal inocula of S. Java and P. putida strains P1 or P3 were simultaneously applied, the interaction was characterized by mutual inhibition, whereas P. putida strain P2 showed an exploitation of S. Java. Lowering the inoculum density of S. Java changed the interaction with P. putida strain P3 also into an exploitation of S. Java. A further increase in S. Java inhibition was established by P. putida strain P3 forming a mature biofilm before applying S. Java.

Conclusions

This study provides the first results showing the potential of P. putida as BCA against S. Java in the broiler environment. Future work should include more complex microbial communities residing in the DWS, additional Salmonella strains as well as chemicals typically used to clean and disinfect the system.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-020-02046-5.

Establishment of a New PNA-FISH Method for Aspergillus fumigatus Identification: First Insights for Future Use in Pulmonary Samples

Aspergillus fumigatus is the main causative agent of Invasive Aspergillosis. This mold produces conidia that when inhaled by immunocompromized hosts can be deposited in the lungs and germinate, triggering disease. In this paper, the development of a method using peptide nucleic acid-fluorescence in situ hybridization (PNA-FISH) is described. The PNA-FISH probe was tested in several strains and a specificity and sensitivity of 100% was obtained. Detection of A. fumigatussensu stricto was then achieved in artificial sputum medium (ASM) pre-inoculated with 1 × 10² conidia·mL^-1-1 × 10³ conidia·mL^-1, after a germination step of 24 h. The PNA-FISH method was evaluated in 24 clinical samples (10 sputum, 8 bronchoalveolar lavage (BAL), and 6 bronchial lavage (BL)) that were inoculated with 1 × 10⁴ conidia·mL^-1 in sputum; 1 × 10³ conidia·mL^-1 in BL and BAL, for 24 h. Despite a specificity of 100%, the sensitivity was 79%. This relatively low sensitivity can be explained by the fact that hyphae can yield "fungal ball" clusters, hindering pipetting procedures and subsequent detection, leading to false negative results. Nonetheless, this study showed the potential of the PNA-FISH method for A. fumigatussensu stricto detection since it takes only 1 h 30 m to perform the procedure with a pre-enrichment step of 6 h (pure cultures) and 24 h (clinical samples), and might provide a suitable alternative to the existing methods for studies in pure cultures and in clinical settings.

Antibacterial efficacy of R-type pyocins against Pseudomonas aeruginosa on biofilms and in a murine model of acute lung infection

BACKGROUND

The appearance of MDR strains and the development of biofilms make Pseudomonas aeruginosa infections a therapeutic challenge. To overcome this scenario, bacteriocins have been proposed as a potential adjuvant or alternative to antibiotic treatment.

OBJECTIVES

To study the activity of R-pyocins on biofilms and in a murine model of pneumonia using a high-risk clone of P. aeruginosa.

METHODS

The activity of R-pyocins on P. aeruginosa biofilms was tested on bacteria attached to a silicone surface, before and after biofilm formation. The effectiveness of R1-pyocin was studied in a murine model of pneumonia using ST175, a high-risk clone of P. aeruginosa.

RESULTS

R-pyocins attacked adherent bacteria, preventing biofilm formation, and penetrated into the biofilm, killing P. aeruginosa within it, resulting in a dramatic reduction in bacterial load. R1-pyocin was active in a murine model of P. aeruginosa lung infection, administered before infection as a preventive treatment, and in acute pneumonia, with efficiency higher than standard colistin treatment. In addition, this work is the first to describe histopathological lung changes after administration of R-pyocins, contributing to the resolution of P. aeruginosa pneumonia in a murine model.

CONCLUSIONS

This work highlights the potential use of the R-pyocins as therapeutic agents, alone or as adjuvants, due to its effectiveness on biofilms and in a murine model of pneumonia using ST175, a high-risk clone of P. aeruginosa. It may thus be feasible to consider R-pyocins as a possible therapeutic alternative in XDR infections, where treatment alternatives are limited.

Techniques to Assess Phage-Biofilm Interaction

Biofilms are ubiquitous in nature found on nearly every type of living and inert surface. They basically consist of microorganisms attached to surfaces and surrounded by a self-produced matrix of extracellular polymeric substances. Phages have proven to be successful in controlling biofilms. Here, we describe methods to characterize phage-biofilm interactions, specifically to assess biofilm biomass and to visualize the biofilm structure, discriminating infected cells using targeted molecular probes.

Characteristics of Biofilms Formed by Co-Culture of Listeria monocytogenes with Pseudomonas aeruginosa at Low Temperatures and Their Sensitivity to Antibacterial Substances

We assessed the properties of biofilms (BFs) formed by mono- and co-cultures of Listeria monocytogenes and Pseudomonas aeruginosa (L+P-BF) at low temperatures and examined their sensitivity to several antibacterial substances. L. monocytogenes viable counts comprised only 1-10% of total L+P-BF viable counts at 10℃ and 15℃, indicating the significant prevalence of P. aeruginosa in co-cultures. L+P-BF formed at 10℃ and 15℃ showed very high resistance to antibiotics and NaClO. Examination of the effects of nattokinase and nisin, natural food additives with antibacterial properties, showed that their application alone failed to inhibit L+P-BF development at 10℃ and 15℃. However, a combined treatment with nisin and ethylenediaminetetraacetic acid, a food additive that can be used as a permeabilizing agent, suppressed the formation of L+P-BF at 10℃ and 15℃. Microscopy observations of L+P-BF did not reveal pronounced morphological changes in bacterial cell morphology. We also noted that P. aeruginosa resistance to the action of nisin during BF formation was higher when it was maintained in co-culture with L. monocytogenes. The results of the present study are an important step toward developing a safe formulation of acceptable food additives that could be used for suppression of BFs formed by pathogenic bacteria during food storage.

Chestnut Honey and Bacteriophage Application to Control Pseudomonas aeruginosa and Escherichia coli Biofilms: Evaluation in an ex vivo Wound Model

Chronic skin wounds represent a major burn both economically and socially. Pseudomonas aeruginosa and Escherichia coli are among the most common colonizers of infected wounds and are prolific biofilm formers. Biofilms are a major problem in infections due to their increasingly difficult control and eradication, and tolerance to multiple prescribed drugs. As so, alternative methods are necessary. Bacteriophages (phages) and honey are both seen as a promising approach for biofilm related infections. Phages have specificity toward a bacterial genus, species or even strain, self-replicating nature, and avoid dysbiosis. Honey has gained acknowledgment due to its antibacterial, antioxidant and anti-inflammatory and wound healing properties. In this work, the effect of E. coli and P. aeruginosa phages vB_EcoS_CEB_EC3a and vB_PaeP_PAO1-D and chestnut honey, alone and combined, were tested using in vitro (polystyrene) and ex vivo (porcine skin) models and against mono and dual-species biofilms of these bacteria. In general, colonization was higher in the porcine skins and the presence of a second microorganism in a consortium of species did not affect the effectiveness of the treatments. The antibacterial effect of combined therapy against dual-species biofilms led to bacterial reductions that were greater for biofilms formed on polystyrene than on skin. Monospecies biofilms of E. coli were better destroyed with phages and honey than P. aeruginosa monospecies biofilms. Overall, the combined phage-honey formulations resulted in higher efficacies possibly due to honey's capacity to damage the bacterial cell membrane and also to its ability to penetrate the biofilm matrix, promoting and enhancing the subsequent phage infection.

Role of nutrient limitation in the competition between uropathogenic strains of Klebsiella pneumoniae and Escherichia coli in mixed biofilms

Klebsiella pneumoniae and Escherichia coli form mixed species biofilms in catheter-associated urinary tract infections. Recently, a detrimental effect of K. pneumoniae over E. coli was observed in mixed species biofilms grown in an artificial urine medium. The mechanism behind this competitive interaction was studied. K. pneumoniae partially outcompeted E. coli in early-stage batch-fed biofilms, whereas both microorganisms co-exist at longer times (K. pneumoniae:E. coli ratio, 55:1), as shown by cell counts and confocal microscopy. E. coli cells were scattered along the K. pneumoniae biofilm. Biofilm supernatants did not appear to contain either antimicrobial or anti-biofilm activities against E. coli. Biofilms grown under continuous flow prevented interspecies competition. K. pneumoniae showed both increased siderophore production and better growth in iron-limited media compared to E. coli. In summary, these results indicate the importance of nutrient (particularly iron) competition in the modulation of the bacterial composition of mixed species biofilms formed by uropathogenic K. pneumoniae and E. coli.

SEM Analysis of Surface Impact on Biofilm Antibiotic Treatment

The aim of this work was to use scanning electron microscopy (SEM) to investigate the effect of ampicillin treatment on Escherichia coli biofilms formed on two surface materials with different properties, silicone (SIL) and glass (GLA). Epifluorescence microscopy (EM) was initially used to assess biofilm formation and killing efficiency on both surfaces. This technique showed that higher bacterial colonization was obtained in the hydrophobic SIL than in the hydrophilic GLA. It has also shown that higher biofilm inactivation was attained for GLA after the antibiotic treatment (7-log reduction versus 1-log reduction for SIL). Due to its high resolution and magnification, SEM enabled a more detailed analysis of the antibiotic effect on biofilm cells, complementing the killing efficiency information obtained by EM. SEM micrographs revealed that ampicillin-treated cells have an elongated form when compared to untreated cells. Additionally, it has shown that different materials induced different levels of elongation on cells exposed to antibiotic. Biofilms formed on GLA showed a 37% higher elongation than those formed on SIL. Importantly, cell elongation was related to viability since ampicillin had a higher bactericidal effect on GLA-formed biofilms. These findings raise the possibility of using SEM for understanding the efficacy of antimicrobial treatments by observation of biofilm morphology.

Impact of polymicrobial biofilms in catheter-associated urinary tract infections

Recent reports have demonstrated that most biofilms involved in catheter-associated urinary tract infections are polymicrobial communities, with pathogenic microorganisms (e.g. Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae) and uncommon microorganisms (e.g. Delftia tsuruhatensis, Achromobacter xylosoxidans) frequently co-inhabiting the same urinary catheter. However, little is known about the interactions that occur between different microorganisms and how they impact biofilm formation and infection outcome. This lack of knowledge affects CAUTIs management as uncommon bacteria action can, for instance, influence the rate at which pathogens adhere and grow, as well as affect the overall biofilm resistance to antibiotics. Another relevant aspect is the understanding of factors that drive a single pathogenic bacterium to become prevalent in a polymicrobial community and subsequently cause infection. In this review, a general overview about the IMDs-associated biofilm infections is provided, with an emphasis on the pathophysiology and the microbiome composition of CAUTIs. Based on the available literature, it is clear that more research about the microbiome interaction, mechanisms of biofilm formation and of antimicrobial tolerance of the polymicrobial consortium are required to better understand and treat these infections.

Ecological networking of cystic fibrosis lung infections

In the context of a polymicrobial infection, treating a specific pathogen poses challenges because of unknown consequences on other members of the community. The presence of ecological interactions between microbes can change their physiology and response to treatment. For example, in the cystic fibrosis lung polymicrobial infection, antimicrobial susceptibility testing on clinical isolates is often not predictive of antibiotic efficacy. Novel approaches are needed to identify the interrelationships within the microbial community to better predict treatment outcomes. Here we used an ecological networking approach on the cystic fibrosis lung microbiome characterized using 16S rRNA gene sequencing and metagenomics. This analysis showed that the community is separated into three interaction groups: Gram-positive anaerobes, Pseudomonas aeruginosa, and Staphylococcus aureus. The P. aeruginosa and S. aureus groups both anti-correlate with the anaerobic group, indicating a functional antagonism. When patients are clinically stable, these major groupings were also stable, however, during exacerbation, these communities fragment. Co-occurrence networking of functional modules annotated from metagenomics data supports that the underlying taxonomic structure is driven by differences in the core metabolism of the groups. Topological analysis of the functional network identified the non-mevalonate pathway of isoprenoid biosynthesis as a keystone for the microbial community, which can be targeted with the antibiotic fosmidomycin. This study uses ecological theory to identify novel treatment approaches against a polymicrobial disease with more predictable outcomes.

Modulation of the Substitution Pattern of 5-Aryl-2-Aminoimidazoles Allows Fine-Tuning of Their Antibiofilm Activity Spectrum and Toxicity

We previously synthesized several series of compounds, based on the 5-aryl-2-aminoimidazole scaffold, that showed activity preventing the formation of Salmonella enterica serovar Typhimurium and Pseudomonas aeruginosa biofilms. Here, we further studied the activity spectrum of a number of the most active N1- and 2N-substituted 5-aryl-2-aminoimidazoles against a broad panel of biofilms formed by monospecies and mixed species of bacteria and fungi. An N1-substituted compound showed very strong activity against the biofilms formed by Gram-negative and Gram-positive bacteria and the fungus Candida albicans but was previously shown to be toxic against various eukaryotic cell lines. In contrast, 2N-substituted compounds were nontoxic and active against biofilms formed by Gram-negative bacteria and C. albicans but had reduced activity against biofilms formed by Gram-positive bacteria. In an attempt to develop nontoxic compounds with potent activity against biofilms formed by Gram-positive bacteria for application in antibiofilm coatings for medical implants, we synthesized novel compounds with substituents at both the N1 and 2N positions and tested these compounds for antibiofilm activity and toxicity. Interestingly, most of these N1-,2N-disubstituted 5-aryl-2-aminoimidazoles showed very strong activity against biofilms formed by Gram-positive bacteria and C. albicans in various setups with biofilms formed by monospecies and mixed species but lost activity against biofilms formed by Gram-negative bacteria. In light of application of these compounds as anti-infective coatings on orthopedic implants, toxicity against two bone cell lines and the functionality of these cells were tested. The N1-,2N-disubstituted 5-aryl-2-aminoimidazoles in general did not affect the viability of bone cells and even induced calcium deposition. This indicates that modulating the substitution pattern on positions N1 and 2N of the 5-aryl-2-aminoimidazole scaffold allows fine-tuning of both the antibiofilm activity spectrum and toxicity.

Role of interspecies interactions in dual-species biofilms developed in vitro by uropathogens isolated from polymicrobial urinary catheter-associated bacteriuria

Most catheter-associated urinary tract infections are polymicrobial. Here, uropathogen interactions in dual-species biofilms were studied. The dual-species associations selected based on their prevalence in clinical settings were Klebsiella pneumoniae-Escherichia coli, E. coli-Enterococcus faecalis, K. pneumoniae-E. faecalis, and K. pneumoniae-Proteus mirabilis. All species developed single-species biofilms in artificial urine. The ability of K. pneumoniae to form biofilms was not affected by E. coli or E. faecalis co-inoculation, but was impaired by P. mirabilis. Conversely, P. mirabilis established a biofilm when co-inoculated with K. pneumoniae. Additionally, E. coli persistence in biofilms was hampered by K. pneumoniae but not by E. faecalis. Interestingly, E. coli, but not K. pneumoniae, partially inhibited E. faecalis attachment to the surface and retarded biofilm development. The findings reveal bacterial interactions between uropathogens in dual-species biofilms ranged from affecting initial adhesion to outcompeting one bacterial species, depending on the identity of the partners involved.

Impact of Delftia tsuruhatensis and Achromobacter xylosoxidans on Escherichia coli dual-species biofilms treated with antibiotic agents

Recently it was demonstrated that for urinary tract infections species with a lower or unproven pathogenic potential, such as Delftia tsuruhatensis and Achromobacter xylosoxidans, might interact with conventional pathogenic agents such as Escherichia coli. Here, single- and dual-species biofilms of these microorganisms were characterized in terms of microbial composition over time, the average fitness of E. coli, the spatial organization and the biofilm antimicrobial profile. The results revealed a positive impact of these species on the fitness of E. coli and a greater tolerance to the antibiotic agents. In dual-species biofilms exposed to antibiotics, E. coli was able to dominate the microbial consortia in spite of being the most sensitive strain. This is the first study demonstrating the protective effect of less common species over E. coli under adverse conditions imposed by the use of antibiotic agents.

Discrimination of bacteriophage infected cells using locked nucleic acid fluorescent in situ hybridization (LNA-FISH)

Bacteriophage-host interaction studies in biofilm structures are still challenging due to the technical limitations of traditional methods. The aim of this study was to provide a direct fluorescence in situ hybridization (FISH) method based on locked nucleic acid (LNA) probes, which targets the phage replication phase, allowing the study of population dynamics during infection. Bacteriophages specific for two biofilm-forming bacteria, Pseudomonas aeruginosa and Acinetobacter, were selected. Four LNA probes were designed and optimized for phage-specific detection and for bacterial counterstaining. To validate the method, LNA-FISH counts were compared with the traditional plaque forming unit (PFU) technique. To visualize the progression of phage infection within a biofilm, colony-biofilms were formed and infected with bacteriophages. A good correlation (r = 0.707) was observed between LNA-FISH and PFU techniques. In biofilm structures, LNA-FISH provided a good discrimination of the infected cells and also allowed the assessment of the spatial distribution of infected and non-infected populations.

Quorum-Quenching and Matrix-Degrading Enzymes in Multilayer Coatings Synergistically Prevent Bacterial Biofilm Formation on Urinary Catheters

Bacteria often colonize in-dwelling medical devices and grow as complex biofilm communities of cells embedded in a self-produced extracellular polymeric matrix, which increases their resistance to antibiotics and the host immune system. During biofilm growth, bacterial cells cooperate through specific quorum-sensing (QS) signals. Taking advantage of this mechanism of biofilm formation, we hypothesized that interrupting the communication among bacteria and simultaneously degrading the extracellular matrix would inhibit biofilm growth. To this end, coatings composed of the enzymes acylase and α-amylase, able to degrade bacterial QS molecules and polysaccharides, respectively, were built on silicone urinary catheters using a layer-by-layer deposition technique. Multilayer coatings of either acylase or amylase alone suppressed the biofilm formation of corresponding Gram-negative Pseudomonas aeruginosa and Gram-positive Staphylococcus aureus. Further assembly of both enzymes in hybrid nanocoatings resulted in stronger biofilm inhibition as a function of acylase or amylase position in the layers. Hybrid coatings, with the QS-signal-degrading acylase as outermost layer, demonstrated 30% higher antibiofilm efficiency against medically relevant Gram-negative bacteria compared to that of the other assemblies. These nanocoatings significantly reduced the occurrence of single-species (P. aeruginosa) and mixed-species (P. aeruginosa and Escherichia coli) biofilms on silicone catheters under both static and dynamic conditions. Moreover, in an in vivo animal model, the quorum quenching and matrix degrading enzyme assemblies delayed the biofilm growth up to 7 days.

Cells of Escherichia coli are protected against severe chemical stress by co-habiting cell aggregates formed by Pseudomonas aeruginosa

Bacterial cells within biofilms and cell aggregates show increased resistance against chemical stress compared with suspended cells. It is not known whether bacteria that co-habit biofilms formed by other bacteria also acquire such resistance. This scenario was investigated in a proof-of-principle experiment with Pseudomonas aeruginosa strain PAO1 as cell aggregate-forming bacterium and Escherichia coli strain MG1655 as potential co-habiting bacterium equipped with an inducible bioluminescence system. Cell aggregation of strain PAO1 can be induced by the toxic detergent sodium dodecyl sulfate (SDS). In single cultures of strain MG1655, bioluminescence was inhibited by the protonophor carbonylcyanide-m-chlorophenylhydrazone (CCCP) but the cells were still viable. By applying CCCP and SDS together, cells of strain MG1655 lost their bioluminescence and viability indicating the importance of energy-dependent resistance mechanisms against SDS. In co-suspensions with strain PAO1, bioluminescence of strain MG1655 was sustained in the presence of SDS and CCCP. Image analysis showed that bioluminescent cells were located in cell aggregates formed by strain PAO1. Thus, cells of strain MG1655 that co-habited cell aggregates formed by strain PAO1 were protected against a severe chemical stress that was lethal to them in single cultures. Co-habiting could lead to increased survival of pathogens in clinical settings and could be employed in biotechnological applications involving toxic milieus.

Fast and effective photodynamic inactivation of multiresistant bacteria by cationic riboflavin derivatives

Photodynamic inactivation of bacteria (PIB) proves to be an additional method to kill pathogenic bacteria. PIB requires photosensitizer molecules that effectively generate reactive oxygen species like singlet oxygen when exposed to visible light. To allow a broad application in medicine, photosensitizers should be safe when applied in humans. Substances like vitamin B2, which are most likely safe, are known to produce singlet oxygen upon irradiation. In the present study, we added positive charges to flavin derivatives to enable attachment of these molecules to the negatively charged surface of bacteria. Two of the synthesized flavin derivatives showed a high quantum yield of singlet oxygen of approximately 75%. Multidrug resistant bacteria like MRSA (Methicillin resistant Staphylococcus aureus), EHEC (enterohemorrhagic Escherichia coli), Pseudomonas aeruginosa, and Acinetobacter baumannii were incubated with these flavin derivatives in vitro and were subsequently irradiated with visible light for seconds only. Singlet oxygen production in bacteria was proved by detecting its luminescence at 1270 nm. After irradiation, the number of viable bacteria decreased up to 6 log10 steps depending on the concentration of the flavin derivatives and the light dosimetry. The bactericidal effect of PIB was independent of the bacterial type and the corresponding antibiotic resistance pattern. In contrast, the photosensitizer concentration and light parameters used for bacteria killing did not affect cell viability of human keratinocytes (therapeutic window). Multiresistant bacteria can be safely and effectively killed by a combination of modified vitamin B2 molecules, oxygen and visible light, whereas normal skin cells survive. Further work will include these new photosensitizers for topical application to decolonize bacteria from skin and mucosa.

On bacteriocin delivery systems and potential applications

Bacteriocins are antimicrobial peptides produced by a variety of bacteria. These peptides can act as antibiotic synergists or alternatives to enhance the therapeutic effects of current infection treatments and decrease the prevalence of resistant strains. Two bacteriocins, namely nisin and pediocin PA-1, are currently being used by the food industry; however, the introduction of these and others into the biomedical industry, and further development of food applications, have been challenged by the slow development of reliable delivery systems. For bacteriocins, these systems rely on novel and pre-existing technologies. Many essential variables need to be accounted for to formulate successful delivery methods. In this review, documented and potential bacteriocin delivery systems are examined, with special attention paid to how those systems are being implemented in the food and medical industries.

Interaction between atypical microorganisms and E. coli in catheter-associated urinary tract biofilms

Most biofilms involved in catheter-associated urinary tract infections (CAUTIs) are polymicrobial, with disease causing (eg Escherichia coli) and atypical microorganisms (eg Delftia tsuruhatensis) frequently inhabiting the same catheter. Nevertheless, there is a lack of knowledge about the role of atypical microorganisms. Here, single and dual-species biofilms consisting of E. coli and atypical bacteria (D. tsuruhatensis and Achromobacter xylosoxidans), were evaluated. All species were good biofilm producers (Log 5.84-7.25 CFU cm(-2) at 192 h) in artificial urine. The ability of atypical species to form a biofilm appeared to be hampered by the presence of E. coli. Additionally, when E. coli was added to a pre-formed biofilm of the atypical species, it seemed to take advantage of the first colonizers to accelerate adhesion, even when added at lower concentrations. The results suggest a greater ability of E. coli to form biofilms in conditions mimicking the CAUTIs, whatever the pre-existing microbiota and the inoculum concentration.

Escherichia coli adhesion, biofilm development and antibiotic susceptibility on biomedical materials

The aim of this work was to test materials typically used in the construction of medical devices regarding their influence in the initial adhesion, biofilm development and antibiotic susceptibility of Escherichia coli biofilms. Adhesion and biofilm development was monitored in 12-well microtiter plates containing coupons of different biomedical materials--silicone (SIL), stainless steel (SS) and polyvinyl chloride (PVC)--and glass (GLA) as control. The susceptibility of biofilms to ciprofloxacin and ampicillin was assessed, and the antibiotic effect in cell morphology was observed by scanning electron microscopy. The surface hydrophobicity of the bacterial strain and materials was also evaluated from contact angle measurements. Surface hydrophobicity was related with initial E. coli adhesion and subsequent biofilm development. Hydrophobic materials, such as SIL, SS, and PVC, showed higher bacterial colonization than the hydrophilic GLA. Silicone was the surface with the greatest number of adhered cells and the biofilms formed on this material were also less susceptible to both antibiotics. It was found that different antibiotics induced different levels of elongation on E. coli sessile cells. Results revealed that, by affecting the initial adhesion, the surface properties of a given material can modulate biofilm buildup and interfere with the outcome of antimicrobial therapy. These findings raise the possibility of fine-tuning surface properties as a strategy to reach higher therapeutic efficacy.

Collagen and hyaluronan at wound sites influence early polymicrobial biofilm adhesive events

BACKGROUND

Wounds can easily become chronically infected, leading to secondary health complications, which occur more frequently in individuals with diabetes, compromised immune systems, and those that have suffered severe burns. When wounds become chronically infected, biofilm producing microbes are often isolated from these sites. The presence of a biofilm at a wound site has significant negative impact on the treatment outcomes, as biofilms are characteristically recalcitrant to removal, in part due to the formation of a protective matrix that shield residents organisms from inimical forces. Pseudomonas aeruginosa and methicillin-resistant Staphylococcus aureus (MRSA) are two of the organisms most prevalently isolated from wound sites, and are of particular concern due to their elevated levels of antibiotic resistance, rapid growth, and exotoxin production. In order to understand the biofilm forming abilities of these microbes in a simulated wound environment we used a microtiter plate assay to assess the ability of these two organisms to bind to proteins that are typically found at wound sites: collagen and hyaluronan.

RESULTS

Collagen and hyaluronan were used to coat the wells of 96-well plates in collagen:hyaluronan ratios of 0:1, 3:1, 1:1, 1:3, and 1:0 . P. aeruginosa and MRSA were inoculated as mono- and co-cultures (1:1 and a 3:1 MRSA: P. aeruginosa). We determined that coating the wells with collagen and/or hyaluronan significantly increased the biofilm biomass of attached cells compared to an uncoated control, although no one coating formulation showed a significant increase compared to any other combination. We also noted that the fold-change increase for MRSA upon coating was greater than for P. aeruginosa.

CONCLUSIONS

Our study suggests that the presence of collagen and/or hyaluronan at wound sites may be an important factor that influences the attachment and subsequent biofilm formation of notorious biofilm-formers, such as MRSA and P. aeruginosa. Understanding the kinetics of binding may aid in our comprehension of recalcitrant wound infection development, better enabling our ability to design therapies that would prevent or mitigate the negative outcomes associated with such infections.

Inhibition of biofilm formation by T7 bacteriophages producing quorum-quenching enzymes

Bacterial growth in biofilms is the major cause of recalcitrant biofouling in industrial processes and of persistent infections in clinical settings. The use of bacteriophage treatment to lyse bacteria in biofilms has attracted growing interest. In particular, many natural or engineered phages produce depolymerases to degrade polysaccharides in the biofilm matrix and allow access to host bacteria. However, the phage-produced depolymerases are highly specific for only the host-derived polysaccharides and may have limited effects on natural multispecies biofilms. In this study, an engineered T7 bacteriophage was constructed to encode a lactonase enzyme with broad-range activity for quenching of quorum sensing, a form of bacterial cell-cell communication via small chemical molecules (acyl homoserine lactones [AHLs]) that is necessary for biofilm formation. Our results demonstrated that the engineered T7 phage expressed the AiiA lactonase to effectively degrade AHLs from many bacteria. Addition of the engineered T7 phage to mixed-species biofilms containing Pseudomonas aeruginosa and Escherichia coli resulted in inhibition of biofilm formation. Such quorum-quenching phages that can lyse host bacteria and express quorum-quenching enzymes to affect diverse bacteria in biofilm communities may become novel antifouling and antibiofilm agents in industrial and clinical settings.