Hacking into bacterial biofilms: a new therapeutic challenge

Choline and geranate ionic liquid for subgingival biofilm control

Periodontitis is a chronic inflammatory disease that causes destruction of the periodontium and eventual tooth loss. The priority in the periodontal treatment is to remove the subgingival biofilm. Chemical removal of biofilms using antimicrobial agents has been applied in clinical practice. However, their clinical effect is still limited because the agents must overcome biofilm's significant drug tolerance, which is primarily caused by the extracellular matrix, a physical barrier that attenuates drug diffusion. This study aimed to study the use of ionic liquids (ILs), a new class of biocompatible materials, for controlling subgingival biofilms because of their excellent permeability. Choline and geranate (CAGE) IL was tested for its highly potent antiseptic behavior and permeability. Antibacterial tests revealed that the significant efficacy of CAGE against periodontopathic microorganisms was derived from their ability to destroy cell membrane, as demonstrated by membrane permeability assay and transmission electron microscopy imaging. Antibiofilm tests using two pathogenic biofilm models revealed that CAGE exerted efficacy against the biofilm-embedded bacteria, conspicuously neutralized the biofilms, and eventually destroyed the biofilm structure. Furthermore, the penetration of CAGE into the biofilm was visually confirmed using confocal laser scanning microscopy. This study highlighted the potential of CAGE as a powerful antibiofilm therapeutic.

Advanced Imaging Methodology in Bacterial Biofilms with a Fluorescent Enzymatic Sensor for pepN Activity

This research explores the use of the pepN activity fluorescent sensor DCM-Ala in bacterial biofilms, emphasizing its significance due to the critical role of biofilms in various biological processes. Advanced imaging techniques were employed to visualize pepN activity, introducing a novel approach to examining biofilm maturity. We found that the overexpression of pepN increases the ability of E. coli to form biofilm. The findings demonstrate varying levels of pepN activity throughout biofilm development, suggesting potential applications in biofilm research and management. The results indicate that the fluorescent emission from this sensor could serve as a reliable indicator of biofilm maturity, and the imaging techniques developed could enhance our understanding and control of biofilm-related processes. This work highlights the importance of innovative methods in biofilm study and opens new avenues for utilizing chemical emissions in biofilm management.

Fungal versus non-fungal supra-inguinal prosthetic vascular graft infections: A cohort study

OBJECTIVES

Fungal prosthetic vascular graft infections are rare and mainly supra-inguinal. Current guidelines are based on the few studies that have specifically investigated this population, with few risk factors described. The objective of this study is to compare fungal and non-fungal supra-inguinal prosthetic vascular graft infections (PVGI), describing their specificities, identifying risk factors, and evaluating outcomes.

PATIENTS AND METHODS

This is a single-center retrospective cohort study carried out at the Pitié-Salpêtrière Hospital in Paris, including all patients who were treated for a supra-inguinal PVGI between January 1st, 2009 and February 28th, 2021. Preoperative, intraoperative and postoperative data were compared between fungal and non-fungal PVGI.

RESULTS

Out of the 475 patients screened, 148 developed a supra-inguinal PVGI: 32 fungal and 116 non-fungal. Factors independently associated with fungal PVGI were presence of a prostheto-digestive fistula (OR 5.98; 95% CI 2.29-15.62) and preoperative antibiotic therapy of seven days or more (OR 2.87; 95% CI 1.12-7.38). Mortality rate at 180 days was significantly higher for fungal as compared to non-fungal PVGIs (38% vs. 16% p = 0.009) and for fungal PVGI with prostheto-digestive fistula. However, there was no statistically significant relation between mortality due to prostheto-digestive fistula in contrast with fungal PVGI alone (p = 0.21).

CONCLUSION

Prostheto-digestive fistula was strongly associated with fungal PVGI, which leads us to suggest that in such cases, an anti-fungal agent should be prescribed.

Antibiofilm potential of nanonized eugenol against Pseudomonas aeruginosa

AIMS

The purpose of this study was to synthesize a nanoform of eugenol (an important phytochemical with various pharmacological potentials) and to investigate its antibiofilm efficacy on Pseudomonas aeruginosa biofilm.

METHODS AND RESULTS

Colloidal suspension of eugenol-nanoparticles (ENPs) was synthesized by the simple ultrasonic cavitation method through the emulsification of hydrophobic eugenol into hydrophilic gelatin. Thus, the nanonization process made water-insoluble eugenol into water-soluble nano-eugenol, making the nanoform bioavailable. The size of the ENPs was 20-30 nm, entrapment efficiency of eugenol within gelatin was 80%, and release of eugenol from the gelatin cap was slow and sustained over 5 days. Concerning the clinically relevant pathogen P. aeruginosa, ENPs had higher antibiofilm (for both formation and eradication) activities than free eugenol. Minimal biofilm inhibitory concentration and minimal biofilm eradication concentration of ENP on P. aeruginosa biofilm were 2.0 and 4.0 mM, respectively. In addition, the measurement of P. aeruginosa biofilm biomass, biofilm thickness, amount of biofilm extra-polymeric substance, cell surface hydrophobicity, cell swarming and twitching efficiencies, cellular morphology, and biofilm formation in catheter demonstrated that the antibiofilm efficacy of nano-eugenol was 30%-40% higher than that of bulk eugenol.

CONCLUSION

These results signify that future pharmacological and clinical studies are very much required to investigate whether ENPs can act as an effective drug against P. aeruginosa biofilm-mediated diseases. Thus, the problem of intrinsic antibiotic tolerance of biofilm-forming cells may be minimized by ENPs. Moreover, ENP may be used as a potential catheter-coating agent to inhibit pseudomonal colonization on catheter surfaces and, therefore, to reduce catheter-associated infections and complications.

Isolation of Aeromonas salmonicida subspecies salmonicida from aquaculture environment in India: Polyphasic identification, virulence characterization, and antibiotic susceptibility

This study reports the polyphasic identification, characterization of virulence potential, and antibiotic susceptibility of Aeromonas salmonicida subspecies salmonicida COFCAU_AS, isolated from an aquaculture system in India. The physiological, biochemical, 16s rRNA gene sequencing and PAAS PCR test identified the strain as Aeromonas salmonicida. The MIY PCR tests established the subspecies as 'salmonicida'. The in vitro tests showed the isolated bacterium as haemolytic with casein, lipid, starch, and gelatin hydrolysis activity, indicating its pathogenic attributes. It also showed the ability to produce slime and biofilm, and additionally, it possessed an A-layer surface protein. In vivo pathogenicity test was performed to determine the LD₅₀ dose of the bacterium in Labeo rohita fingerlings (14.42 ± 1.01 g), which was found to be 10^6.9 cells fish^-1. The bacteria-challenged fingerlings showed skin lesions, erythema at the base of the fins, dropsy, and ulcer. Almost identical clinical signs and mortalities were observed when the same LD₅₀ dose was injected into other Indian major carp species, L. catla and Cirrhinus mrigala. Out of the twelve virulent genes screened, the presence of nine genes viz., aerA, act, ast, alt, hlyA, vapA, exsA, fstA, and lip were detected, whereas ascV, ascC, and ela genes were absent. The A. salmonicida subsp. salmonicida COFCAU_AS was resistant to antibiotics such as penicillin G, rifampicin, ampicillin, and vancomycin while highly sensitive to amoxiclav, nalidixic acid, chloramphenicol, ciprofloxacin, and tetracycline. In summary, we have isolated a virulent A. salmonicida subsp. salmonicida from a tropical aquaculture pond which can cause significant mortality and morbidity in Indian major carp species.

Bacteriophages as Biotechnological Tools

Bacteriophages are ubiquitous organisms that can be specific to one or multiple strains of hosts, in addition to being the most abundant entities on the planet. It is estimated that they exceed ten times the total number of bacteria. They are classified as temperate, which means that phages can integrate their genome into the host genome, originating a prophage that replicates with the host cell and may confer immunity against infection by the same type of phage; and lytics, those with greater biotechnological interest and are viruses that lyse the host cell at the end of its reproductive cycle. When lysogenic, they are capable of disseminating bacterial antibiotic resistance genes through horizontal gene transfer. When professionally lytic-that is, obligately lytic and not recently descended from a temperate ancestor-they become allies in bacterial control in ecological imbalance scenarios; these viruses have a biofilm-reducing capacity. Phage therapy has also been advocated by the scientific community, given the uniqueness of issues related to the control of microorganisms and biofilm production when compared to other commonly used techniques. The advantages of using bacteriophages appear as a viable and promising alternative. This review will provide updates on the landscape of phage applications for the biocontrol of pathogens in industrial settings and healthcare.

Antiadherent AgBDC Metal-Organic Framework Coating for Escherichia coli Biofilm Inhibition

Surface microbial colonization and its potential biofilm formation are currently a major unsolved problem, causing almost 75% of human infectious diseases. Pathogenic biofilms are capable of surviving high antibiotic doses, resulting in inefficient treatments and, subsequently, raised infection prevalence rates. Antibacterial coatings have become a promising strategy against the biofilm formation in biomedical devices due to their biocidal activity without compromising the bulk material. Here, we propose for the first time a silver-based metal-organic framework (MOF; here denoted AgBDC) showing original antifouling properties able to suppress not only the initial bacterial adhesion, but also the potential surface contamination. Firstly, the AgBDC stability (colloidal, structural and chemical) was confirmed under bacteria culture conditions by using agar diffusion and colony counting assays, evidencing its biocide effect against the challenging E. coli, one of the main representative indicators of Gram-negative resistance bacteria. Then, this material was shaped as homogeneous spin-coated AgBDC thin film, investigating its antifouling and biocide features using a combination of complementary procedures such as colony counting, optical density or confocal scanning microscopy, which allowed to visualize for the first time the biofilm impact generated by MOFs via a specific fluorochrome, calcofluor.

A newly isolated bacteriophage vB8388 and its synergistic effect with aminoglycosides against multi-drug resistant Klebsiella oxytoca strain FK-8388

The bacteriophage vB8388 can lyse multi-drug resistant Klebsiella oxytoca strain FK-8388 and maintain stability in a wide range of temperatures (from 4 °C to 80 °C) and pHs (3-11). Bioinformatics analysis showed that vB8388 is a linear double-stranded DNA virus that is 39,750 long with 50.65% G + C content and 44 putative open reading frames (ORFs). Phage vB8388 belongs to the family Autographviridae and possesses a non-contractile tail. The latency period of vB8388 was approximately 20 min. The combination of phage vB8388 and gentamicin, amikacin, or tobramycin could effectively inhibit the growth of K. oxytoca strain FK-8388, with a decrease of more than 4 log units within 12 h in vitro. Phage vB8388 showed a strong synergistic effect with gentamicin that could enhance the anti-biofilm effect of vB8388. The phage + gentamicin combination also showed synergy in vivo in the larval infection model of Galleria mellonella. In conclusion, the findings of this study suggest the potential of phage + antibiotic combination therapy to be used as an alternative therapeutic approach for treating infectious diseases caused by multidrug-resistant bacteria.

Factors Influencing Biofilm Formation by Salmonella enterica sv. Typhimurium, E. cloacae, E. hormaechei, Pantoea spp., and Bacillus spp. Isolated from Human Milk Determined by PCA Analysis

Bacteria enter milk during poor hygiene practices and can form a biofilm on surfaces that come into contact with human milk. The presence of a biofilm increases the risk of infections among newborns as bacteria protected by biofilm are resistant to washing and disinfection processes. The formation of the biofilm depends on the microbial species, environmental conditions, and the specific materials colonized. The aim of this study is to analyze the effects of factors such as temperature, incubation time, and initial cell concentration on biofilm formation by pathogenic bacteria isolated from human milk on model hydrophobic polystyrene surfaces. Model studies confirm that pathogenic bacteria appearing in human milk as a result of cross-contamination tend to form a biofilm. The majority of isolates formed biofilm at both 25 and 37 °C after 12 h at 1 × 10³ CFU/mL inoculum count. Multivariate principal component analysis (PCA) showed that at lower temperatures, biofilm formation by bacterial isolates was the main determinant of biofilm formation, other factors were less important; however, at 37 °C, time was a factor in biofilm formation. The model research performed underlines the importance of maintaining the proper hygiene of rooms, surfaces, and devices for expressing, storing, and preparing mothers' milk and powdered infant formula (PIF) in facilities responsible for feeding newborns and premature babies.

Antibiotic-free antimicrobial poly (methyl methacrylate) bone cements: A state-of-the-art review

Prosthetic joint infection (PJI) is the most serious complication following total joint arthroplasty, this being because it is associated with, among other things, high morbidity and low quality of life, is difficult to prevent, and is very challenging to treat/manage. The many shortcomings of antibiotic-loaded poly (methyl methacrylate) (PMMA) bone cement (ALBC) as an agent for preventing and treating/managing PJI are well-known. One is that microorganisms responsible for most PJI cases, such as methicillin-resistant S. aureus, have developed or are developing resistance to gentamicin sulfate, which is the antibiotic in the vast majority of approved ALBC brands. This has led to many research efforts to develop cements that do not contain gentamicin (or, for that matter, any antibiotic) but demonstrate excellent antimicrobial efficacy. There is a sizeable body of literature on these so-called "antibiotic-free antimicrobial" PMMA bone cements (AFAMBCs). The present work is a comprehensive and critical review of this body. In addition to summaries of key trends in results of characterization studies of AFAMBCs, the attractive features and shortcomings of the literature are highlighted. Shortcomings provide motivation for future work, with some ideas being formulation of a new generation of AFAMBCs by, example, adding a nanostructured material and/or an extract from a natural product to the powder and/or liquid of the basis cement, respectively.

A drug-free strategy to combat bacterial infections with magnetic nanoparticles biosynthesized in bacterial pathogens

The extensive and indiscriminate use of antibiotics in the ongoing COVID-19 pandemic might significantly contribute to the growing number of multiple drug resistant (MDR) bacteria. With the dwindling pipeline of new and effective antibiotics, we might soon end up in a post-antibiotic era, in which even common bacterial infections would be a challenge to control. To prevent this, an antibiotic-free strategy would be highly desirable. Magnetic nanoparticle (MNP)-mediated hyperthermia-induced antimicrobial therapy is an attractive option as it is considered safe for human use. Given that iron and zinc are critical for bacterial virulence, we evaluated the response of multiple pathogenic bacteria to these elements. Treatment with 1 mM iron and zinc precursors resulted in the intracellular biosynthesis of MNPs in multiple Gram-positive and Gram-negative disease-causing bacteria. The superparamagnetic nanoparticles in the treated bacteria/biofilms, generated heat upon exposure to an alternating magnetic field (AMF), which resulted in an increase in the temperature (5-6 °C) of the milieu with a subsequent decrease in bacterial viability. Furthermore, we observed for the first time that virulent bacteria derived from infected samples harbour MNPs, suggesting that the bacteria had biosynthesised the MNPs using the metal ions acquired from the host. AMF treatment of the bacterial isolates from the infected specimens resulted in a strong reduction in viability (3-4 logs) as compared to vancomycin/ciprofloxacin treatment. The therapeutic efficacy of the MNPs to induce bacterial death with AMF alone was confirmed ex vivo using infected tissues. Our proposed antibiotic-free approach for killing bacteria using intracellular MNPs is likely to evolve as a promising strategy to combat a wide range of bacterial infections.

Bacterial biofilm infections, their resistance to antibiotics therapy and current treatment strategies

Nearly 80% of human chronic infections are caused due to bacterial biofilm formation. This is the most leading cause for failure of medical implants resulting in high morbidity and mortality. In addition, biofilms are also known to cause serious problems in food industry. Biofilm impart enhanced antibiotic resistance and become recalcitrant to host immune responses leading to persistent and recurrent infections. It makes the clinical treatment for biofilm infections very difficult. Reduced penetration of antibiotic molecules through EPS, mutation of the target site, accumulation of antibiotic degrading enzymes, enhanced expression of efflux pump genes are the probable causes for antibiotics resistance. Accordingly, strategies like administration of topical antibiotics and combined therapy of antibiotics with antimicrobial peptides are considered for alternate options to overcome the antibiotics resistance. A number of other remediation strategies for both biofilm inhibition and dispersion of established biofilm have been developed. The metallic nanoparticles and their oxides have recently gained a tremendous thrust as antibiofilm therapy for their unique features. This present comprehensive review gives the understanding of antibiotic resistance mechanisms of biofilm and provides an overview of various currently available biofilm remediation strategies, focusing primarily on the applications of metallic nanoparticles and their oxides.

Actinobacillus pleuropneumoniae Surviving on Environmental Multi-Species Biofilms in Swine Farms

Actinobacillus pleuropneumoniae is the etiologic agent of porcine contagious pleuropneumonia, an important respiratory disease for the pig industry. A. pleuropneumoniae has traditionally been considered an obligate pig pathogen. However, its presence in the environment is starting to be known. Here, we report the A. pleuropneumoniae surviving in biofilms in samples of drinking water of swine farms from Mexico. Fourteen farms were studied. Twenty drinking water samples were positive to A. pleuropneumoniae distributed on three different farms. The bacteria in the drinking water samples showed the ability to form biofilms in vitro. Likewise, A. pleuropneumoniae biofilm formation in situ was observed on farm drinkers, where the biofilm formation was in the presence of other bacteria such as Escherichia coli, Stenotrophomonas maltophilia, and Acinetobacter schindleri. Our data suggest that A. pleuropneumoniae can inhabit aquatic environments using multi-species biofilms as a strategy to survive outside of their host.

Antimicrobial and antibiofilm activities of Cu(II) Schiff base complexes against methicillin-susceptible and resistant Staphylococcus aureus

Background

Methicillin-resistance S. aureus (MRSA) possesses the ability to resist multiple antibiotics and form biofilm. Currently, vancomycin remains the last drug of choice for treatment of MRSA infection. The emergence of vancomycin-resistant S. aureus (VRSA) has necessitated the development of new therapeutic agents against MRSA. In this study, the antimicrobial and antibiofilm activities of two copper-complexes derived from Schiff base (SBDs) were tested individually, and in combination with oxacillin (OXA) and vancomycin (VAN) against reference strains methicillin-susceptible and methicillin-resistant Staphylococcus aureus. The toxicity of the SBDs was also evaluated on a non-cancerous mammalian cell line.

Methods

The antimicrobial activity was tested against the planktonic S. aureus cells using the microdilution broth assay, while the antibiofilm activity were evaluated using the crystal violet and resazurin assays. The cytotoxicity of the SBDs was assessed on MRC5 (normal lung tissue), using the MTT assay.

Results

The individual SBDs showed significant reduction of biomass and metabolic activity in both S. aureus strains. Combinations of the SBDs with OXA and VAN were mainly additive against the planktonic cells and cells in the biofilm. Both the compounds showed moderate toxicity against the MRC5 cell line. The selectivity index suggested that the compounds were more cytotoxic to S. aureus than the normal cells.

Conclusion

Both the SBD compounds demonstrated promising antimicrobial and antibiofilm activities and have the potential to be further developed as an antimicrobial agent against infections caused by MRSA.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12941-021-00473-4.

Biofilm and its implications postfracture fixation: All I need to know

Biofilm represents an organized multicellular community of bacteria having a complex 3D structure, formed by bacterial cells and their self-produced extracellular matrix. It usually attaches to any foreign body or fixation implant. It acts as a physical protective barrier of the bacteria from the penetration of antibodies, bacteriophages, granulocytes and biocides, antiseptics, and antibiotics. Biofilm-related infections will increase in the near future. This group of surgical site infections is the most difficult to diagnose, to suppress, to eradicate, and in general to manage. Multispecialty teams involved in all stages of care are an effective way to improve results and save resources and time for the benefit of patients and the health system. Significant steps have occurred recently in the prevention and development of clever tools that we can employ in this everlasting fight with the bacteria. Herein, we attempt to describe the nature and role of the "biofilm" to the specific clinical setting of surgical site infections in the field of orthopaedic trauma surgery.

Surface engineered iron oxide nanoparticles as efficient materials for antibiofilm application

Overuse of antibiotics has led to the development of multi drug resistant strains. Antibiotic resistance is a major drawback in the biomedical field since medical implants are prone to infection by biofilms of antibiotic resistant strains of bacteria. With increasing prevalence of antibiotic resistant pathogenic bacteria, the search for alternative method is utmost importance. In this regard, magnetic nanoparticles are commonly used as a substitute for antibiotics that can circumvent the problem of biofilms growth on the surface of biomedical implants. Iron oxide nanoparticles (IONPs) have unique magnetic properties that can be exploited in various ways in the biomedical applications. IONPs are engineered employing different methods to induce surface functionalization that include the use of polyethyleneimine and oleic acid. IONPs have a mechanical effect on biofilms when in presence of an external magnet. In this review, a detailed description of surface engineered magnetic nanoparticles as ideal antibacterial agents is provided, accompanied by various methods of literature review. This article is protected by copyright. All rights reserved.

Bacterial biofilm-derived antigens: a new strategy for vaccine development against infectious diseases

INTRODUCTION

Microorganisms can develop into a social organization known as biofilms and these communities can be found in virtually all types of environment on earth. In biofilms, cells grow as multicellular communities held together by a self-produced extracellular matrix. Living within a biofilm allows for the emergence of specific properties for these cells that their planktonic counterparts do not have. Furthermore, biofilms are the cause of several infectious diseases and are frequently inhabited by multi-species. These interactions between microbial species are often critical for the biofilm process. Despite the importance of biofilms in disease, vaccine antigens are typically prepared from bacteria grown as planktonic cells under laboratory conditions. Vaccines based on planktonic bacteria may not provide optimal protection against biofilm-driven infections.

AREAS COVERED

In this review, we will present an overview of biofilm formation, what controls this mode of growth, and recent vaccine development targeting biofilms.

EXPERT OPINION

Previous and ongoing research provides evidence that vaccine formulation with antigens derived from biofilms is a promising approach to prevent infectious diseases and can enhance the protective efficacy of existing vaccines. Therefore, research focusing on the identification of biofilm-derived antigens merits further investigations.

Attenuation of Pseudomonas aeruginosa biofilm by thymoquinone: an individual and combinatorial study with tetrazine-capped silver nanoparticles and tryptophan

Microbial biofilm indicates a cluster of microorganisms having the capability to display drug resistance property, thereby increasing its proficiency in spreading diseases. In the present study, the antibiofilm potential of thymoquinone, a black seed-producing natural molecule, was contemplated against the biofilm formation by Pseudomonas aeruginosa. Substantial antimicrobial activity was exhibited by thymoquinone against the test organism wherein the minimum inhibitory concentration of the compound was found to be 20 μg/mL. Thereafter, an array of experiments (crystal violet staining, protein count, and microscopic observation, etc.) were carried out by considering the sub-MIC doses of thymoquinone (5 and 10 μg/mL), each of which confirmed the biofilm attenuating capacity of thymoquinone. However, these concentrations did not show any antimicrobial activity. Further explorations on understanding the underlying mechanism of the same revealed that thymoquinone accumulated reactive oxygen species (ROS) and also inhibited the expression of the quorum sensing gene (lasI) in Pseudomonas aeruginosa. Furthermore, by taking up a combinatorial approach with two other reported antibiofilm agents (tetrazine-capped silver nanoparticles and tryptophan), the antibiofilm efficiency of thymoquinone was expanded. In this regard, the highest antibiofilm activity was observed when thymoquinone, tryptophan, and tetrazine-capped silver nanoparticles were applied together against Pseudomonas aeruginosa. These combinatorial applications of antibiofilm molecules were found to accumulate ROS in cells that resulted in the inhibition of biofilm formation. Thus, the combinatorial study of these antibiofilm molecules could be applied to control biofilm threats as the tested antibiofilm molecules alone or in combinations showed negligible or very little cytotoxicity.

PA5001 gene involves in swimming motility and biofilm formation in Pseudomonas aeruginosa

Pseudomonas aeruginosa is a nosocomial human pathogen causing infections in immunocompromised patients. To explore new genes involved in P. aeruginosa swimming motility, Mu transposon mutagenesis library was screened for isolates with altered swimming motility. Eleven nonmobile mutants were identified. Sequence analysis shows the nonmobile phenotype of one isolate was attributed to the inactivation of PA5001 gene. PA5001 knockout mutant based on the PAK lab strain also displayed comparable phenotypes suggesting the universal gene function regardless of strain. Exotic PA5001 gene fragment provided on expressing plasmid was capable of storing nonmobile phenotype of PA5001 mutant, suggesting the functional involvement of PA5001 gene on bacterial swimming. Impact of PA5001 inactivation on biofilm formation was examined, as adhesion and interaction during biofilm formation is highly dependent of bacterial mobility. The result shows that normal architecture of biofilm was disrupted in the mutant. Complementing by exotic PA5001 gene fragment resulted in the restoration of biofilm phenotype. Our results provide evidences suggesting the functional participation of PA5001 gene in bacterial mobility and biofilm formation. The critical function by PA5001 in bacterial motility and biofilm might serve as hint for the novel target for the treatment of chronic infections caused by P. aeruginosa.

Inhibition of biofilm formation of Pseudomonas aeruginosa by caffeine: a potential approach for sustainable management of biofilm

Pseudomonas aeruginosa is a potent biofilm forming organism causing several diseases on host involving biofilm. Several natural and synthetic molecules have been explored towards inhibiting the biofilm formation of Pseudomonas aeruginosa. In the current report, the role of a natural molecule namely caffeine was examined against the biofilm forming ability of P. aeruginosa. We have observed that caffeine shows substantial antimicrobial activity against P. aeruginosa wherein the minimum inhibitory concentration (MIC) of caffeine was found to be 200 μg/mL. The antibiofilm activity of caffeine was determined by performing a series of experiments using its sub-MIC concentrations (40 and 80 μg/mL). The results revealed that caffeine can significantly inhibit the biofilm development of P. aeruginosa. Caffeine has been found to interfere with the quorum sensing of P. aeruginosa by targeting the swarming motility. Molecular docking analysis further indicated that caffeine can interact with the quorum sensing proteins namely LasR and LasI. Thus, the result indicated that caffeine could inhibit the formation of biofilm by interfering with the quorum sensing of the organism. Apart from biofilm inhibition, caffeine has also been found to reduce the secretion of virulence factors from Pseudomonas aeruginosa. Taken together, the results revealed that in addition to biofilm inhibition, caffeine can also decrease the spreading of virulence factors from Pseudomonas aeruginosa.

Reduction of Pseudomonas aeruginosa biofilm formation through the application of nanoscale vibration

Bacterial biofilms pose a significant burden in both healthcare and industrial environments. With the limited effectiveness of current biofilm control strategies, novel or adjunctive methods in biofilm control are being actively pursued. Reported here, is the first evidence of the application of nanovibrational stimulation (nanokicking) to reduce the biofilm formation of Pseudomonas aeruginosa. Nanoscale vertical displacements (approximately 60 nm) were imposed on P. aeruginosa cultures, with a significant reduction in biomass formation observed at frequencies between 200 and 4000 Hz at 24 h. The optimal reduction of biofilm formation was observed at 1 kHz, with changes in the physical morphology of the biofilms. Scanning electron microscope imaging of control and biofilms formed under nanovibrational stimulation gave indication of a reduction in extracellular matrix (ECM). Quantification of the carbohydrate and protein components of the ECM was performed and showed a significant reduction at 24 h at 1 kHz frequency. To model the forces being exerted by nanovibrational stimulation, laser interferometry was performed to measure the amplitudes produced across the Petri dish surfaces. Estimated peak forces on each cell, associated with the nanovibrational stimulation technique, were calculated to be in the order of 10 pN during initial biofilm formation. This represents a potential method of controlling microbial biofilm formation in a number of important settings in industry and medical related processes.

An Ag-loaded photoactive nano-metal organic framework as a promising biofilm treatment

Surface biofilm inhibition is still currently a considerable challenge. Among other organisms, Staphylococcus aureus is notable for its ability to form a strong biofilm with proved resistance to chemotherapy. Contamination of high-touch surfaces with S. aureus biofilm not only promotes disease spread but also generates tremendous health-associated costs. Therefore, development of new bactericidal and antiadhesive surface coatings is a priority. Considering that metal-organic frameworks (MOFs) have recently emerged as promising antibacterial agents, we originally report here the synthesis of a multi-active silver-containing nanoscaled MOF composite as a potential surface coating against S. aureus biofilm owing to a triple effect: intrinsic bactericide activity of the MOF, biocidal character of silver nanoparticles (AgNPs), and photoactivity after UVA irradiation. AgNPs were successfully entrapped within the benchmarked nanoscaled porous photoactive titanium(IV) aminoterephthalate MIL-125(Ti)NH₂ using a simple and efficient impregnation-reduction method. After complete characterization of the composite thin film, its antibacterial and anti-adherent properties were fully evaluated. After UVA irradiation, the composite coating exhibited relevant bacterial inhibition and detachment, improved ligand-to-cluster charge transfer, and steady controlled delivery of Ag⁺. These promising results establish the potential of this composite as an active coating for biofilm treatment on high-touch surfaces (e.g., surgical devices, door knobs, and rail bars). STATEMENT OF SIGNIFICANCE: Surface contamination due to bacterial biofilm formation is still a demanding issue, as it causes severe disease spread. One possible solution is the development of antifouling and antibacterial surface coatings. In this work, we originally propose the use of photoactive metal-organic frameworks (MOFs) for biofilm treatment. The novelty of this work relies on the following: i) the treatment of strongly contaminated surfaces, as previous studies with MOFs have exclusively addressed biofilm prevention; ii) this pioneering work reports both antiadherent effect, which removes the biofilm, and bacterial inhibition; iii) our original successful strategy has never been proposed thus far, involving the multi-active combination of 1) intrinsic antibacterial effect of a photoactive titanium-based nanoMOF, 2) immobilization of biocide silver nanoparticles, and 3) improved anti-bioadherent effect upon irradiation of the composite coating.

Antibiofilm activity of the essential oil of citronella (Cymbopogon nardus) and its major component, geraniol, on the bacterial biofilms of Staphylococcus aureus

Medicinal plants with antimicrobial action have been investigated for uses against biofilms, among which, Cymbopogon nardus, citronella, stands out as a promising species. The present study aims to evaluate the antimicrobial and antibiofilm action of the essential oil of C. nardus (EOCN) and geraniol on Gram-negative and positive bacteria from the determination of minimum inhibitory concentration (MIC) and minimum bactericidal concentration and inhibition of biofilms. In the results, the EOCN produced a 41 mm halo on S. aureus, which was susceptible with MIC values of 0.5 and 0.25 mg/mL for the EOCN and geraniol respectively, both with bactericidal effect. The antibiofilm action was confirmed, the EOCN and geraniol reduced the biofilm biomass of S. aureus up to 100% between 0.5 and 4 mg/mL concentrations. The reduction of cell viability was 0.25 and 1 mg/mL, of EOCN and geraniol, respectively. EOCN and geraniol were shown to be promising antibiotic against S. aureus.

In Vitro Comparison of Antibacterial and Antibiofilm Activities of Selected Fluoroquinolones against Pseudomonas aeruginosa and Methicillin-Resistant Staphylococcus aureus

An in vitro overview of the inhibitory effects of selected fluoroquinolones against planktonic and biofilm cells of the methicillin-resistant Staphylococcus aureus (MRSA) strain American type culture collection (ATCC) 43300 and the Pseudomonas aeruginosa strain ATCC 27853 was carried out. Biofilm cells of both strains were less susceptible to the selected antibiotics than their planktonic counterparts. In addition, certain antibiotics were more effective against biofilm cells, while others performed better on the planktonic cells. Against P. aeruginosa, ciprofloxacin was the most potent on both planktonic and biofilm cells, whereas ofloxacin was the least potent on both biofilm and planktonic cells. Moxifloxacin and gatifloxacin were the most potent against both planktonic and biofilm MRSA bacteria, however, not in the same order of activity. Norfloxacin was the least active when tested against both planktonic and biofilm cells. The results of this work are expected to provide insight into the efficacy of various fluoroquinolones against MRSA and Pseudomonas aeruginosa biofilms. This study could form the basis for future clinical studies that could recommend special guidelines for the management of infections that are likely to involve bacteria in their biofilm state.

Bacterial biofilm formation on implantable devices and approaches to its treatment and prevention

In living organisms, biofilms are defined as complex communities of bacteria residing within an exopolysaccharide matrix that adheres to a surface. In the clinic, they are typically the cause of chronic, nosocomial, and medical device-related infections. Due to the antibiotic-resistant nature of biofilms, the use of antibiotics alone is ineffective for treating biofilm-related infections. In this review, we present a brief overview of concepts of bacterial biofilm formation, and current state-of-the-art therapeutic approaches for preventing and treating biofilms. Also, we have reviewed the prevalence of such infections on medical devices and discussed the future challenges that need to be overcome in order to successfully treat biofilms using the novel technologies being developed.

Effectiveness of omega-3 polyunsaturated fatty acids against microbial pathogens

Microorganisms provide both beneficial and harmful effects to human beings. Beneficial effects come from the symbiotic relationship that exists between humans and microbiota, but then several human illnesses have turned some friendly microbes into opportunistic pathogens, causing several microbial-related diseases. Various efforts have been made to create and utilize antimicrobial agents in the treatment and prevention of these infections, but such efforts have been hampered by the emergence of antimicrobial resistance. Despite extensive studies on drug discovery to alleviate this problem, issues with the toxicity and tolerance of certain compounds and continuous microbial evolution have forced researchers to focus on screening various phytochemical dietary compounds for antimicrobial activity. Linolenic acid and its derivatives (eicosapentaenoic acid and docosahexaenoic acid) are omega-3 fatty acids that have been studied due to their role in human health, being important for the brain, the eye, the cardiovascular system, and general human growth. However, their utilization as antimicrobial agents has not been widely appreciated, perhaps due to a lack of understanding of antimicrobial mechanisms, toxicity, and route of administration. Therefore, this review focuses on the efficacy, mechanism, and toxicity of omega-3 fatty acids as alternative therapeutic agents for treating and preventing diseases associated with pathogenic microorganisms.

Antibiofilm activity of the essential oil of citronella (Cymbopogon nardus) and its major component, geraniol, on the bacterial biofilms of Staphylococcus aureus

Medicinal plants with antimicrobial action have been investigated for uses against biofilms, among which, Cymbopogon nardus, citronella, stands out as a promising species. The present study aims to evaluate the antimicrobial and antibiofilm action of the essential oil of C. nardus (EOCN) and geraniol on Gram-negative and positive bacteria from the determination of minimum inhibitory concentration (MIC) and minimum bactericidal concentration and inhibition of biofilms. In the results, the EOCN produced a 41 mm halo on S. aureus, which was susceptible with MIC values of 0.5 and 0.25 mg/mL for the EOCN and geraniol respectively, both with bactericidal effect. The antibiofilm action was confirmed, the EOCN and geraniol reduced the biofilm biomass of S. aureus up to 100% between 0.5 and 4 mg/mL concentrations. The reduction of cell viability was 0.25 and 1 mg/mL, of EOCN and geraniol, respectively. EOCN and geraniol were shown to be promising antibiotic against S. aureus.

Incorporation of Actinobacillus pleuropneumoniae in Preformed Biofilms by Escherichia coli Isolated From Drinking Water of Swine Farms

Actinobacillus pleuropneumoniae, the etiological agent of porcine pleuropneumonia, represents one of the most important health problems in the swine industry worldwide and it is included in the porcine respiratory disease complex. One of the bacterial survival strategies is biofilm formation, which are bacterial communities embedded in an extracellular matrix that could be attached to a living or an inert surface. Until recently, A. pleuropneumoniae was considered to be an obligate pathogen. However, recent studies have shown that A. pleuropneumoniae is present in farm drinking water. In this study, the drinking water microbial communities of Aguascalientes (Mexico) swine farms were analyzed, where the most frequent isolated bacterium was Escherichia coli. Biofilm formation was tested in vitro; producing E. coli biofilms under optimal growth conditions; subsequently, A. pleuropneumoniae serotype 1 (strains 4074 and 719) was incorporated to these biofilms. Interaction between both bacteria was evidenced, producing an increase in biofilm formation. Extracellular matrix composition of two-species biofilms was also characterized using fluorescent markers and enzyme treatments. In conclusion, results confirm that A. pleuropneumoniae is capable of integrates into biofilms formed by environmental bacteria, indicative of a possible survival strategy in the environment and a mechanism for disease dispersion.

Free tryptophan residues inhibit quorum sensing of Pseudomonas aeruginosa: a potential approach to inhibit the development of microbial biofilm

Microbial biofilm reveals a cluster of microbial population aggregated on a surface. Pseudomonas aeruginosa, a strong biofilm forming organism, often causes several human diseases. Microorganism-based diseases become more difficult to manage when the causative organism develops biofilm during the course of disease progression as the organism attains alarming drug resistance in biofilm form. Agents inhibiting microbial biofilm formation could be considered as a potential tool to weaken the extent of microbial pathogenesis. Tryptophan has already been reported as a promising agent against the biofilm development by P. aeruginosa. In the current study, we had focused on the underlying mechanism of microbial biofilm inhibition of P. aeruginosa under the influence of tryptophan. The expression level of the mRNA of the genes (lasR, lasB and lasI) associated with quorum sensing was compared between tryptophan treated and untreated cells under similar conditions using real time polymerase chain reaction (RT-PCR). The results showed that the tested concentrations of tryptophan considerably reduced the expression of those genes (lasR, lasB and lasI) that are required during the occurrence of quorum sensing in P. aeruginosa. Molecular docking also revealed that tryptophan can interact with the proteins responsible for the occurrence of quorum sensing in P. aeruginosa. The cytotoxicity assay was carried out wherein we observed that the tested concentration of tryptophan did not show any considerable cytotoxicity against the RAW 264.7 macrophage cell line. From this study, it may be concluded that the tryptophan-mediated inhibition of biofilm formation is associated with interference of quorum sensing in P. aeruginosa. Hence, tryptophan could be used as a potential agent against the microbial biofilm mediated pathogenesis.

Synthesis, Antimicrobial and Antioxidant Activity of Pyrazole Based Sulfonamide Derivatives

A series of new sulfonamides have been synthesized from Ampyrone with different benzene sulfonyl chlorides to yield the N-1,5-dimethyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazol-4-yl) benzenesulfonamides (4a-e). All synthesized compounds were characterized on the basis of FTIR, 1H NMR, and 13C NMR, and also by the aid of mass spectral data. Further, all synthesized compounds have studied for their in vitro antimicrobial activities against selected bacterial as well as fungal strains by the agar well diffusion method. Free radical scavenging activity has been investigated by using DPPH method. Among all the synthesized compounds, 4b, 4d, and 4e exhibited significant antimicrobial and antioxidant activities.

A Nonbactericidal Zinc-Complexing Ligand as a Biofilm Inhibitor: Structure-Guided Contrasting Effects on Staphylococcus aureus Biofilm

Zinc-complexing ligands are prospective anti-biofilm agents because of the pivotal role of zinc in the formation of Staphylococcus aureus biofilm. Accordingly, the potential of a thiosemicarbazone (compound C1) and a benzothiazole-based ligand (compound C4) in the prevention of S. aureus biofilm formation was assessed. Compound C1 displayed a bimodal activity, hindering biofilm formation only at low concentrations and promoting biofilm growth at higher concentrations. In the case of C4, a dose-dependent inhibition of S. aureus biofilm growth was observed. Atomic force microscopy analysis suggested that at higher concentrations C1 formed globular aggregates, which perhaps formed a substratum that favored adhesion of cells and biofilm formation. In the case of C4, zinc supplementation experiments validated zinc complexation as a plausible mechanism of inhibition of S. aureus biofilm. Interestingly, C4 was nontoxic to cultured HeLa cells and thus has promise as a therapeutic anti-biofilm agent. The essential understanding of the structure-driven implications of zinc-complexing ligands acquired in this study might assist future screening regimes for identification of potent anti-biofilm agents.

New mechanistic insights into the motile-to-sessile switch in various bacteria with particular emphasis on Bacillus subtilis and Pseudomonas aeruginosa: a review

A biofilm is a complex assemblage of microbial communities adhered to a biotic or an abiotic surface which is embedded within a self-produced matrix of extracellular polymeric substances. Many transcriptional regulators play a role in triggering a motile-sessile switch and in consequently producing the biofilm matrix. This review is aimed at highlighting the role of two nucleotide signaling molecules (c-di-GMP and c-di-AMP), toxin antitoxin modules and a novel transcriptional regulator BolA in biofilm formation in various bacteria. In addition, it highlights the common themes that have appeared in recent research regarding the key regulatory components and signal transduction pathways that help Bacillus subtilis and Pseudomonas aeruginosa to acquire the biofilm mode of life.

Inhibition of Pseudomonas aeruginosa by Peptide-Conjugated Phosphorodiamidate Morpholino Oligomers

Pseudomonas aeruginosa is a highly virulent, multidrug-resistant pathogen that causes significant morbidity and mortality in hospitalized patients and is particularly devastating in patients with cystic fibrosis. Increasing antibiotic resistance coupled with decreasing numbers of antibiotics in the developmental pipeline demands novel antibacterial approaches. Here, we tested peptide-conjugated phosphorodiamidate morpholino oligomers (PPMOs), which inhibit translation of complementary mRNA from specific, essential genes in P. aeruginosa PPMOs targeted to acpP, lpxC, and rpsJ, inhibited P. aeruginosa growth in many clinical strains and activity of PPMOs could be enhanced 2- to 8-fold by the addition of polymyxin B nonapeptide at subinhibitory concentrations. The PPMO targeting acpP was also effective at preventing P. aeruginosa PAO1 biofilm formation and at reducing existing biofilms. Importantly, treatment with various combinations of a PPMO and a traditional antibiotic demonstrated synergistic growth inhibition, the most effective of which was the PPMO targeting rpsJ with tobramycin. Furthermore, treatment of P. aeruginosa PA103-infected mice with PPMOs targeting acpP, lpxC, or rpsJ significantly reduced the bacterial burden in the lungs at 24 h by almost 3 logs. Altogether, this study demonstrates that PPMOs targeting the essential genes acpP, lpxC, or rpsJ in P. aeruginosa are highly effective at inhibiting growth in vitro and in vivo These data suggest that PPMOs alone or in combination with antibiotics represent a novel approach to addressing the problems associated with rapidly increasing antibiotic resistance in P. aeruginosa.

Bacteriostatic behavior of surface modulated silicon nitride in comparison to polyetheretherketone and titanium

Perioperative and latent infections are leading causes of revision surgery for orthopaedic devices resulting in significant increased patient care, comorbidities, and attendant costs. Identifying biomaterial surfaces that inherently resist biofilm adhesion and bacterial expression is an important emerging strategy in addressing implant-related infections. This in vitro study was designed to compare biofilm formation on three biomaterials commonly employed in spinal fusion surgery-silicon nitride (Si₃ N₄ ), polyetheretherketone (PEEK), and a titanium alloy (Ti6Al4V-ELI) -using one gram-positive and one gram-negative bacterial species. Disc samples from various surface treated Si₃ N₄ , PEEK, and Ti6Al4V were inoculated with 10⁵ CFU/mm² Staphylococcus epidermidis (ATCC®14990™) or Escherichia coli (ATCC^® 25922™) and cultured in PBS, 7% glucose, and 10% human plasma for 24 and 48 h, followed by retrieval and rinsing. Vortexed solutions were diluted, plated, and incubated at 37 °C for 24 to 48 h. Colony forming units (CFU/mm² ) were determined using applicable dilution factors and surface areas. A two-tailed, heteroscedastic Student's t-test (95% confidence) was used to determine statistical significance. The various Si₃ N₄ samples showed the most favorable bacterial resistance for both bacilli tested. The mechanisms for the bacteriostatic behavior of Si₃ N₄ are likely due to multivariate surface effects including submicron-topography, negative charging, and chemical interactions which form peroxynitrite (an oxidative agent). Si₃ N₄ is a new biomaterial with the apparent potential to inhibit biofilm formation. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1521-1534, 2017.

Thoracic Aortic Graft Infection due to Candida Albicans with Multiple Embolism in the Left-side Vessels of the Body

A 79-year-old Japanese man who had undergone thoracic aortic replacement 10 years prior presented with a 3-day history of sore throat. He was initially diagnosed with pharyngitis; however, multiple emboli in the vessels of the left side of the body were recognized. He was diagnosed with thoracic aortic graft infection caused by Candida albicans, with multiple embolisms. Anti-fungal therapy was initiated, but surgical removal of the graft was not performed because of the high risk associated with the operation, and he eventually died. Inappropriate use of antibiotics might have led to a severe fungal infection. As such, the inappropriate use of antimicrobial agents should be avoided.

Antibiotic Resistant Superbugs: Assessment of the Interrelationship of Occurrence in Clinical Settings and Environmental Niches

The increasing threat to global health posed by antibiotic resistance remains of serious concern. Human health remains at higher risk due to several reported therapeutic failures to many life threatening drug resistant microbial infections. The resultant effects have been prolonged hospital stay, higher cost of alternative therapy, increased mortality, etc. This opinionated review considers the two main concerns in integrated human health risk assessment (i.e., residual antibiotics and antibiotic resistant genes) in various compartments of human environment, as well as clinical dynamics associated with the development and transfer of antibiotic resistance (AR). Contributions of quorum sensing, biofilms, enzyme production, and small colony variants in bacteria, among other factors in soil, water, animal farm and clinical settings were also considered. Every potential factor in environmental and clinical settings that brings about AR needs to be identified for the summative effects in overall resistance. There is a need to embrace coordinated multi-locational approaches and interrelationships to track the emergence of resistance in different niches in soil and water versus the hospital environment. The further integration with advocacy, legislation, enforcement, technological innovations and further research input and recourse to WHO guidelines on antibiotic policy would be advantageous towards addressing the emergence of antibiotic resistant superbugs.

D-amino acids do not inhibit Pseudomonas aeruginosa biofilm formation

Objective

Pseudomonas aeruginosa, a known biofilm‐forming organism, is an opportunistic pathogen that plays an important role in chronic otitis media, tracheitis, cholesteatoma, chronic wounds, and implant infections. Eradication of biofilm infections has been a challenge because the biofilm phenotype provides bacteria with a protective environment from the immune system and antibiotics; thus, there has been great interest in adjunctive molecules that may inhibit biofilm formation or cause biofilm dispersal. There are reports that D‐amino acids may inhibit biofilms. In this study, we test the ability of various D‐amino acids to inhibit P. aeruginosa biofilm formation in vitro.

Study Design

We evaluated the effect of D‐alanine (10 mM), D‐leucine (10 mM), D‐methionine (10 mM), D‐tryptophan (10 mM), and D‐tyrosine (10 uM and 1 mM) on biofilm formation in two commonly studied laboratory strains of P. aeruginosa: PAO1 and PA14.

Methods

Biofilms were grown in 24‐well and 96‐well tissue culture plates, documented photographically and stained with 0.1% crystal violet and solubilized in 33% glacial acetic acid for quantification.

Results

In strains PAO1 and PA14, the addition of D‐amino acids did not result in an inhibitory effect on biofilm growth in 24‐well plates. Repeating the study in 96‐well plates confirmed our findings that D‐amino acids do not inhibit biofilm formation of P. aeruginosa.

Conclusion

We conclude that D‐amino acids only slow the production of biofilms rather than completely prevent biofilm formation; therefore, D‐amino acids represent a poor option for potential clinically therapeutic interventions.

Level of Evidence

N/A.

Allee effect: the story behind the stabilization or extinction of microbial ecosystem

A population exhibiting Allee effect shows a positive correlation between population fitness and population size or density. Allee effect decides the extinction or conservation of a microbial population and thus appears to be an important criterion in population ecology. The underlying factor of Allee effect that decides the stabilization and extinction of a particular population density is the threshold or the critical density of their abundance. According to Allee, microbial populations exhibit a definite, critical or threshold density, beyond which the population fitness of a particular population increases with the rise in population density and below it, the population fitness goes down with the decrease in population density. In particular, microbial population displays advantageous traits such as biofilm formation, expression of virulence genes, spore formation and many more only at a high population density. It has also been observed that microorganisms exhibiting a lower population density undergo complete extinction from the residual microbial ecosystem. In reference to Allee effect, decrease in population density or size introduces deleterious mutations among the population density through genetic drift. Mutations are carried forward to successive generations resulting in its accumulation among the population density thus reducing its microbial fitness and thereby increasing the risk of extinction of a particular microbial population. However, when the microbial load is high, the chance of genetic drift is less, and through the process of biofilm formation, the cooperation existing among the microbial population increases that increases the microbial fitness. Thus, the high microbial population through the formation of microbial biofilm stabilizes the ecosystem by increasing fitness. Taken together, microbial fitness shows positive correlation with the ecosystem conservation and negative correlation with ecosystem extinction.

Biofilm is associated with chronic streptococcal meningoencephalitis in fish

Biofilms are aggregates of attached microbial organisms whose existence on tissues is often recognised as a mechanism for the establishment of most chronic diseases. Herein we investigated the ability of piscine Streptococcus agalactiae, an important aquatic pathogen, for adaptation to this sessile lifestyle in vitro and in the brain of a tilapia fish model. Piscine S. agalactiae exhibited a weak attachment to polystyrene plates and expressed a low biofilm phenotype under the study conditions. Furthermore, fluorescent in situ hybridization and confocal laser scanning microscopy revealed discrete aggregates of attached S. agalactiae within brain tissues and around meningeal surfaces. They were embedded in an exopolysaccharide containing matrix, intractable to inflammatory response and showed some level of resistance to penicillin despite proven susceptibility on sensitivity test. Intracellular bacterial aggregates were also observed, moreover, antibody mediated response was not demonstrated during infection. Nucleated erythrocytes appear to facilitate brain invasion possibly via the Trojan horse mechanism leading to a granulomatous inflammation. We have demonstrated that biofilm is associated with persistence of S. agalactiae and the development of chronic meningoencephalitis in fish.

Exploring interactions between pathogens and the Drosophila gut

Gastrointestinal infection can provoke substantial disturbance at both a local as well as at a systemic level and may evolve into a chronic disease state. Our growing knowledge of gut-pathogen interactions has been based to a large extent on the use of genetically tractable model hosts such as the fruit fly Drosophila melanogaster. In this review we will summarise the growing literature and critically address the advantages and disadvantages of using this model to extrapolate results from studying pathogen virulence and intestinal responses to humans.

Efficient Eradication of Mature Pseudomonas aeruginosa Biofilm via Controlled Delivery of Nitric Oxide Combined with Antimicrobial Peptide and Antibiotics

Fast eradication of mature biofilms is the ‘holy grail’ in the clinical management of device-related infections. Endogenous nitric oxide (NO) produced by macrophages plays an important role in host defense against intracellular pathogens, and NO is a promising agent in preventing biofilms formation in vitro. However, the rate of delivery of NO by various NO donors (e.g., diazeniumdiolates, S-nitrosothiols, etc.) is difficult to control, which hinders fundamental studies aimed at understanding the role of NO in biofilm control. In this study, by using a novel precisely controlled electrochemical NO releasing catheter device, we examine the effect of physiological levels of NO on eradicating mature Pseudomonas aeruginosa biofilm (7 days), as well as the potential application of the combination of NO with antimicrobial agents. It is shown that physiological levels of NO exhibit mixed effects of killing bacteria and dispersing ambient biofilm. The overall biofilm-eradicating effect of NO is quite efficient in a dose-dependent manner over a 3 h period of NO treatment. Moreover, NO also greatly enhances the efficacy of antimicrobial agents, including human beta-defensin 2 (BD-2) and several antibiotics, in eradicating biofilm and its detached cells, which otherwise exhibited high recalcitrance to these antimicrobial agents. The electrochemical NO release technology offers a powerful tool in evaluating the role of NO in biofilm control as well as a promising approach when combined with antimicrobial agents to treat biofilm-associated infections in hospital settings, especially infections resulting from intravascular catheters.

Vertically aligned multi walled carbon nanotubes prevent biofilm formation of medically relevant bacteria

A significant part of human infections is frequently associated with the establishment of biofilms by (opportunistic) pathogens. Due to the increasing number of untreatable biofilms, there is a rising need to develop novel and effective strategies to prevent biofilm formation on surfaces in medical as well as in technical areas. Bacterial initial attachment and adhesion to surfaces followed by biofilm formation is highly influenced by the physical properties of the surfaces. Consequently, changing these properties or applying different nanostructures is an attractive approach to prevent biofilm formation. Here we report on the effect(s) of surface grown and anchored vertically aligned multi walled carbon nanotubes (MWCNT), which have been made wettable by immersion through a graded ethanol series, on biofilm formation of Klebsiella oxytoca, Pseudomonas aeruginosa, and Staphylococcus epidermidis. We evaluated the biofilm formation under continuous flow conditions by confocal laser scanning microscopy and scanning electron microscopy, and demonstrated significant inhibition of biofilm formation of all the different pathogens by MWCNT of different lengths. Furthermore, the anti-adhesive effects of the MWCNT increased with their overall length. The application potential of our findings on surface grown and anchored vertically aligned MWCNT may represent a suitable contact mechanics based approach to prevent biofilm formation on medical devices or technical sensors operating in fluid environments.

New Perspectives on the Use of Phytochemicals as an Emergent Strategy to Control Bacterial Infections Including Biofilms

The majority of current infectious diseases are almost untreatable by conventional antibiotic therapy given the advent of multidrug-resistant bacteria. The degree of severity and the persistence of infections are worsened when microorganisms form biofilms. Therefore, efforts are being applied to develop new drugs not as vulnerable as the current ones to bacterial resistance mechanisms, and also able to target bacteria in biofilms. Natural products, especially those obtained from plants, have proven to be outstanding compounds with unique properties, making them perfect candidates for these much-needed therapeutics. This review presents the current knowledge on the potentialities of plant products as antibiotic adjuvants to restore the therapeutic activity of drugs. Further, the difficulties associated with the use of the existing antibiotics in the treatment of biofilm-related infections are described. To counteract the biofilm resistance problems, innovative strategies are suggested based on literature data. Among the proposed strategies, the use of phytochemicals to inhibit or eradicate biofilms is highlighted. An overview on the use of phytochemicals to interfere with bacterial quorum sensing (QS) signaling pathways and underlying phenotypes is provided. The use of phytochemicals as chelating agents and efflux pump inhibitors is also reviewed.

The Hybrid Histidine Kinase LadS Forms a Multicomponent Signal Transduction System with the GacS/GacA Two-Component System in Pseudomonas aeruginosa

In response to environmental changes, Pseudomonas aeruginosa is able to switch from a planktonic (free swimming) to a sessile (biofilm) lifestyle. The two-component system (TCS) GacS/GacA activates the production of two small non-coding RNAs, RsmY and RsmZ, but four histidine kinases (HKs), RetS, GacS, LadS and PA1611, are instrumental in this process. RetS hybrid HK blocks GacS unorthodox HK autophosphorylation through the formation of a heterodimer. PA1611 hybrid HK, which is structurally related to GacS, interacts with RetS in P. aeruginosa in a very similar manner to GacS. LadS hybrid HK phenotypically antagonizes the function of RetS by a mechanism that has never been investigated. The four sensors are found in most Pseudomonas species but their characteristics and mode of signaling may differ from one species to another. Here, we demonstrated in P. aeruginosa that LadS controls both rsmY and rsmZ gene expression and that this regulation occurs through the GacS/GacA TCS. We additionally evidenced that in contrast to RetS, LadS signals through GacS/GacA without forming heterodimers, either with GacS or with RetS. Instead, we demonstrated that LadS is involved in a genuine phosphorelay, which requires both transmitter and receiver LadS domains. LadS signaling ultimately requires the alternative histidine-phosphotransfer domain of GacS, which is here used as an Hpt relay by the hybrid kinase. LadS HK thus forms, with the GacS/GacA TCS, a multicomponent signal transduction system with an original phosphorelay cascade, i.e. H1LadS→D1LadS→H2GacS→D2GacA. This highlights an original strategy in which a unique output, i.e. the modulation of sRNA levels, is controlled by a complex multi-sensing network to fine-tune an adapted biofilm and virulence response.

Targeting Biofilm Associated Staphylococcus aureus Using Resazurin Based Drug-susceptibility Assay

Most pathogenic bacteria are able to form biofilms during infection, but due to the difficulty of manipulating and assessing biofilms, the vast majority of laboratory work is conducted with planktonic cells. Here, we describe a peg plate biofilm assay as performed with Staphylococcus aureus. Bacterial biofilms are grown on pegs attached to a 96-well microtiter plate lid, washed through gentle submersion in buffer, and placed in a drug challenge plate. After subsequent incubation they are again washed and moved to a final recovery plate, in which the fluorescent dye resazurin serves as a viability indicator. This assay offers greatly increased ease-of-use, reliability, and reproducibility, as well as a wealth of data when conducted as a kinetic read. Moreover, this assay can be adapted to a medium-throughput drug screening approach by which an endpoint fluorescent readout is taken instead, offering a path for drug discovery efforts.