Cis-2-decenoic acid inhibits S. aureus growth and biofilm in vitro: a pilot study

Antibiotic adjuvant activities of quorum sensing signal molecules DSF and BDSF against mature biofilms of Staphylococci

Among promising antibiofilm compounds, quorum-sensing (QS) molecules that regulate biological processes such as biofilm formation and intra- or interspecies communication appear to be good candidates. The invitro antibiotic-adjuvant effects of QS molecules diffusible signal factor (DSF) and B. cenocepacia producing-DSF (BDSF) were investigated against mature Staphylococcal biofilms. Broth microdilution methods were used for the determinations of MIC, MBC, MBIC, and MBEC, and bactericidal activities were determined by TKC method. The lowest MICs were obtained with ciprofloxacin and gentamicin, and MBECs with ciprofloxacin. DSF and BDSF at 0.5 µM decreased the MICs as 2-8, and 2-32 fold, respectively. In TKC studies, -cidal activities were achieved by BDSF + gentamycin, or ciprofloxacin, and DSF + daptomycin, vancomycin, meropenem or gentamycin combinations. Synergistic effects were generally obtained with BDSF + gentamicin combinations, followed by DSF + daptomycin against most S. aureus; while BDSF + gentamicin or ciprofloxacin, and DSF + vancomycin or meropenem were synergist against some S. epidermidis biofilms. Also, the antagonist effects were observed with BDSF + meropenem or ciprofloxacin against each MSSE and MSSA. It is estimated that these QS molecules, although it was strain dependent, generally enhanced the antibiotic activity, and would be a new and effective treatment strategy for biofilm control, either alone or as an antibiotic adjuvant.

Cis-2-Decenoic Acid and Bupivacaine Delivered from Electrospun Chitosan Membranes Increase Cytokine Production in Dermal and Inflammatory Cell Lines

Wound dressings serve to protect tissue from contamination, alleviate pain, and facilitate wound healing. The biopolymer chitosan is an exemplary choice in wound dressing material as it is biocompatible and has intrinsic antibacterial properties. Infection can be further prevented by loading dressings with cis-2-decenoic acid (C2DA), a non-antibiotic antimicrobial agent, as well as bupivacaine (BUP), a local anesthetic that also has antibacterial capabilities. This study utilized a series of assays to elucidate the responses of dermal cells to decanoic anhydride-modified electrospun chitosan membranes (DA-ESCMs) loaded with C2DA and/or BUP. Cytocompatibility studies determined the toxic loading ranges for C2DA, BUP, and combinations, revealing that higher concentrations (0.3 mg of C2DA and 1.0 mg of BUP) significantly decreased the viability of fibroblasts and keratinocytes. These high concentrations also inhibited collagen production by fibroblasts, with lower loading concentrations promoting collagen deposition. These findings provide insight into preliminary cellular responses to DA-ESCMs and can guide future research on their clinical application as wound dressings.

In vitro and in silico cholinesterase inhibitory potential of metabolites from Laurencia snackeyi (Weber-van Bosse) M. Masuda

Alzheimer's disease (AD) is a neurodegenerative disease that causes deterioration in intelligence and psychological activities. Yet, till today, no cure is available for AD. The marine environment is an important sink of bioactive compounds with neuroprotective potential with reduced adverse effects. Recently, we collected the red algae Laurencia snackeyi from Terumbu Island, Malaysia which is known to be rich in halogenated metabolites making it the most sought-after red algae for pharmaceutical studies. The red alga was identified based on basic morphological characteristics, microscopic observation and chemical data from literature. The purplish-brown algae was confirmed a new record. In Malaysia, this species is poorly documented in Peninsular Malaysia as compared to its eastern continent Borneo. Thus, this study intended to investigate the diversity of secondary metabolites present in the alga and its cholinesterase inhibiting potential for AD. The extract inhibited both acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) with IC50 values of  14.45 ± 0.34 μ g mL-1 and 39.59 ± 0.24 μ g mL-1, respectively. Subsequently, we isolated the synderanes, palisadin A (1), aplysistatin (2) and 5-acetoxypalisadin B (3) that was not exhibit potential. Mass spectrometry analysis detected at total of 33 additional metabolites. The computational aided molecular docking using the AChE and BChE receptors on all metabolites shortlisted 5,8,11,14-eicosatetraynoic acid (31) and 15-hydroxy-1-[2-(hydroxymethyl)-1-piperidinyl]prost-13-ene-1,9-dione (42) with best inhibitory properties, respectively with the lowest optimal combination of S-score and RMSD values. This study shows the unexplored potential of marine natural resources, however, obtaining sufficient biomass for detailed investigation is an uphill task. Regardless, there is a lot of potential for future prospects with a wide range of marine natural resources to study and the incorporation of synthetic chemistry, in vivo studies in experimental design.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03725-6.

Cell-Free Supernatant of Bacillus thuringiensis Displays Anti-Biofilm Activity Against Staphylococcus aureus

Staphylococcus aureus is an important bacterial pathogen responsible for biofilm formation in medical devices. Due to the increasing antibiotic resistance of S. aureus, it is necessary to search for new anti-biofilm agents. In this study, the cell-free supernatant of Bacillus thuringiensis inhibited biofilm formation up to 93% and dispersed biofilms up to 83% without affecting the growth of S. aureus. The ethyl acetate extract of B. thuringiensis cell-free supernatant exhibited a dose-dependent anti-biofilm activity against S. aureus with the biofilm inhibition concentration ranging from 8 to 64 µg/mL. Scanning electron microscopy revealed that the cell-free supernatant extract of B. thuringiensis resulted in a significant reduction in S. aureus biofilms. The ethyl acetate extract of cell-free supernatant of B. thuringiensis was found to contain various compounds with structural similarity to known anti-biofilm compounds. In particular, squalene, cinnamic acid derivatives, and eicosapentaene seem to act synergistically against S. aureus biofilms. Hence, B. thuringiensis cell-free supernatant proved to be effective against S. aureus biofilms. The results clearly show the potential of natural molecules produced by B. thuringiensis as alternative therapies with anti-biofilm activity instead of bactericidal properties.

Dispersive biofilm from membrane bioreactor strains: effects of diffusible signal factor addition and characterization by dispersion index

INTRODUCTION

Biofilm occurs ubiquitously in water system. Excessive biofilm formation deteriorates severely system performance in several water and wastewater treatment processes. Quorum sensing systems were controlled in this study with a signal compound cis-2-Decenoic acid (CDA) to regulate various functions of microbial communities, including motility, enzyme production, and extracellular polymeric substance (EPS) production in biofilm.

METHODS

The addition of CDA to six strains extracted from membrane bioreactor sludge and the Pseudomonas aeruginosa PAO1 strain was examined for modulating biofilm development by regulating DSF expression.

RESULTS AND DISCUSSION

As the CDA doses increased, optical density of the biofilm dispersion assay increased, and the decrease in EPS of the biofilm was obvious on membrane surfaces. The three-dimensional visual images and quantitative analyses of biofilm formation with CDA proved thinner, less massive, and more dispersive than those without; to evaluate its dispersive intensity, a dispersion index was proposed. This could compare the dispersive effects of CDA dosing to other biofilms or efficiencies of biofouling control practices such as backwashing or new cleaning methods.

Innovative Strategies to Overcome Antimicrobial Resistance and Tolerance

Antimicrobial resistance and tolerance are natural phenomena that arose due to evolutionary adaptation of microorganisms against various xenobiotic agents. These adaptation mechanisms make the current treatment options challenging as it is increasingly difficult to treat a broad range of infections, associated biofilm formation, intracellular and host adapted microbes, as well as persister cells and microbes in protected niches. Therefore, novel strategies are needed to identify the most promising drug targets to overcome the existing hurdles in the treatment of infectious diseases. Furthermore, discovery of novel drug candidates is also much needed, as few novel antimicrobial drugs have been introduced in the last two decades. In this review, we focus on the strategies that may help in the development of innovative small molecules which can interfere with microbial resistance mechanisms. We also highlight the recent advances in optimization of growth media which mimic host conditions and genome scale molecular analyses of microbial response against antimicrobial agents. Furthermore, we discuss the identification of antibiofilm molecules and their mechanisms of action in the light of the distinct physiology and metabolism of biofilm cells. This review thus provides the most recent advances in host mimicking growth media for effective drug discovery and development of antimicrobial and antibiofilm agents.

A review on biofilms and the currently available antibiofilm approaches: Matrix-destabilizing hydrolases and anti-bacterial peptides as promising candidates for the food industries

Biofilms are communities of microorganisms that can be harmful and/or beneficial, depending on location and cell content. Since in most cases (such as the formation of biofilms in laboratory/medicinal equipment, water pipes, high humidity-placed structures, and the food packaging machinery) these bacterial and fungal communities are troublesome, researchers in various fields are trying to find a promising strategy to destroy or slow down their formation. In general, anti-biofilm strategies are divided into the plant-based and non-plant categories, with the latter including nanoparticles, bacteriophages, enzymes, surfactants, active peptides and free fatty acids. In most cases, using a single strategy will not be sufficient to eliminate biofilm, and consequently, two or more strategies will inevitably be used to deal with this unwanted phenomenon. According to the analysis of potential biofilm inhibition strategies, the best option for the food industry would be the use of hydrolase enzymes and peptides extracted from natural sources. This article represents a systematic review of the previous efforts made in these directions.

Colonization and Infection of Indwelling Medical Devices by Staphylococcus aureus with an Emphasis on Orthopedic Implants

The use of indwelling medical devices has constantly increased in recent years and has revolutionized the quality of life of patients affected by different diseases. However, despite the improvement of hygiene conditions in hospitals, implant-associated infections remain a common and serious complication in prosthetic surgery, mainly in the orthopedic field, where infection often leads to implant failure. Staphylococcus aureus is the most common cause of biomaterial-centered infection. Upon binding to the medical devices, these bacteria proliferate and develop dense communities encased in a protective matrix called biofilm. Biofilm formation has been proposed as occurring in several stages-(1) attachment; (2) proliferation; (3) dispersal-and involves a variety of host and staphylococcal proteinaceous and non-proteinaceous factors. Moreover, biofilm formation is strictly regulated by several control systems. Biofilms enable staphylococci to avoid antimicrobial activity and host immune response and are a source of persistent bacteremia as well as of localized tissue destruction. While considerable information is available on staphylococcal biofilm formation on medical implants and important results have been achieved on the treatment of biofilms, preclinical and clinical applications need to be further investigated. Thus, the purpose of this review is to gather current studies about the mechanism of infection of indwelling medical devices by S. aureus with a special focus on the biochemical factors involved in biofilm formation and regulation. We also provide a summary of the current therapeutic strategies to combat biomaterial-associated infections and highlight the need to further explore biofilm physiology and conduct research for innovative anti-biofilm approaches.

Dual Antibiotic and Diffusible Signal Factor Combination Nanoliposomes for Combating Staphylococcus epidermidis Biofilm

Purpose: Microbial biofilms are one of the main causes of persistent human infections. Encapsulation of an antibiotic and a biofilm dispersal agent within a nano-carrier has been recognized as a novel approach to combat the problem of biofilm-related infections. Here, we develop the nanoliposomal formulation for delivery of vancomycin in combination with cis-2- decenoic acid (C2DA), to Staphylococcus epidermidis biofilm. The effects of the formulations were studied at two stages: biofilm growth inhabitation and biofilm eradication.

Methods: Liposomal formulations were prepared by the solvent evaporation dehydration-rehydration method and were evaluated for size, zeta potential, and encapsulation efficacy. The ability of different agents in free and encapsulated forms were assessed to evaluate the anti-biofilm activities.

Results: Vancomycin and C2DA were successfully co-encapsulated in the same nanoliposome (liposomal combination). The zeta potential values of the liposomal formulations of vancomycin, C2DA, and the liposomal combination were 37.2, 40.2, 51.5 mV, and the mean sizes of these liposomal formulations were 167.8±1.5, 215.5±8.8, 235.5±0.01, respectively. Encapsulation efficacy of C2DA was 65% and about 40% for vancomycin. The results indicated that liposomal combination exerted strong anti-biofilm activities, slightly exceeding those observed by the free form of a combination of vancomycin and C2DA, but higher than either agent used alone in their free forms. The anti-biofilm activity of formulations followed concentration and time-dependent manner.

Conclusion: The combination of vancomycin and C2DA could inhibit biofilm formation. Employing the liposomal combination is a considerable method to remove bacterial biofilm.

Alternative Approaches for the Management of Diabetic Foot Ulcers

Diabetic foot ulcers (DFU) represent a growing public health problem. The emergence of multidrug-resistant (MDR) bacteria is a complication due to the difficulties in distinguishing between infection and colonization in DFU. Another problem lies in biofilm formation on the skin surface of DFU. Biofilm is an important pathophysiology step in DFU and may contribute to healing delays. Both MDR bacteria and biofilm producing microorganism create hostile conditions to antibiotic action that lead to chronicity of the wound, followed by infection and, in the worst scenario, lower limb amputation. In this context, alternative approaches to antibiotics for the management of DFU would be very welcome. In this review, we discuss current knowledge on biofilm in DFU and we focus on some new alternative solutions for the management of these wounds, such as antibiofilm approaches that could prevent the establishment of microbial biofilms and wound chronicity. These innovative therapeutic strategies could replace or complement the classical strategy for the management of DFU to improve the healing process.

Step-by-step dual stimuli-responsive nanoparticles for efficient bacterial biofilm eradication

Biofilm-related bacterial infections are extremely resistant to antibiotics, mainly due to the impermeability of the intensive matrices, which allow the bacteria to survive antibiotic treatment. Herein, step-by-step dual stimuli-responsive azithromycin-loaded nanoparticles (CM/AZM@Tyr) was constructed for efficient biofilm eradication. CM/AZM@Tyr was prepared by the self-assembly of poly(ε-caprolactone)-polyethylene glycol-polyethylenimine (PCL-PEG-PEI) into cationic micelles and simultaneously encapsulated AZM into the hydrophobic core, which is further bound with cis-aconityl-D-tyrosine (CA-Tyr) through electrostatic interaction. Upon initial penetration, CM/AZM@Tyr could show step-by-step dual-response to the microenvironment of biofilms. Firstly, the CA-Tyr shell rapidly responded to the acidic microenvironment and released D-Tyr to disassemble the biofilm mass. Then, the exposed cationic CM/AZM micelles could bind firmly to the negatively-charged bacteria cell membrane. With the enzymolysis of the PCL core, the rapidly releasing AZM could kill the bacteria over the depth of biofilms. Massive accumulation was observed in the infected lungs of biofilms-associated lung infection mice after the i.v. injection of CM/Cy5.5@Tyr under the 3D mode of the in vivo Imaging System. Reduced bacterial burden and alleviated fibrosis in the infected lungs were also obtained after treatment with CM/AZM@Tyr mainly due to its intensive penetration in the biofilm and the orderly release of the biofilm dispersant and antimicrobial agents. In summary, this research developed an effective strategy for the treatment of blood-accessible biofilm-induced infections.

2-Heptylcyclopropane-1-Carboxylic Acid Disperses and Inhibits Bacterial Biofilms

Fatty-acid signaling molecules can inhibit biofilm formation, signal dispersal events, and revert dormant cells within biofilms to a metabolically active state. We synthesized 2-heptylcyclopropane-1-carboxylic acid (2CP), an analog of cis-2-decenoic acid (C2DA), which contains a cyclopropanated bond that may lock the signaling factor in an active state and prevent isomerization to its least active trans-configuration (T2DA). 2CP was compared to C2DA and T2DA for ability to disperse biofilms formed by Staphylococcus aureus and Pseudomonas aeruginosa. 2CP at 125 μg/ml dispersed approximately 100% of S. aureus cells compared to 25% for C2DA; both 2CP and C2DA had significantly less S. aureus biofilm remaining compared to T2DA, which achieved no significant dispersal. 2CP at 125 μg/ml dispersed approximately 60% of P. aeruginosa biofilms, whereas C2DA and T2DA at the same concentration dispersed 40%. When combined with antibiotics tobramycin, tetracycline, or levofloxacin, 2CP decreased the minimum concentration required for biofilm inhibition and eradication, demonstrating synergistic and additive responses for certain combinations. Furthermore, 2CP supported fibroblast viability above 80% for concentrations below 1 mg/ml. This study demonstrates that 2CP shows similar or improved efficacy in biofilm dispersion, inhibition, and eradication compared to C2DA and T2DA and thus may be promising for use in preventing infection for healthcare applications.

Biofouling detection methods that are widely applicable and useful across disciplines: a mini-review

Biofouling, or the build-up of microorganisms in a biofilm at the solid-water or water-air interface, is an interdisciplinary problem. Biofouling causes various issues including clogging systems, contaminating devices, and creating infections that are extremely difficult to treat, to name but a few. Therefore, engineers, pharmacologists, microbiologists, wastewater treatment operators, chemists, food preservative formulators, home and personal care product formulators, and toxicologists all play a role in studying and have an interest in solving biofouling. High-throughput studies on biofilm prevention and removal can take the form of biofilm antimicrobial microdilution susceptibility (BAMS) tests. Due to vested interests of many disciplines, the results from these tests should be applicable and useful to each discipline. This critical review analyses the focuses, biological implications, and metrics required by each discipline. The possible detection methods that could satisfy each desired metric are then summarized. The detection methods were analysed in order to recommend two methods of biofilm detection, Crystal Violet stain and the LIVE/DEAD BacLight stain, which correspond with three metrics including total biomass, log reduction, and the MIC, BPC, MBIC, MBC, BBC, and/or MBEC values. Determining these three metrics for each BAMS test will allow this type of research to be widely applicable and useful across many disciplines.

In vitro evaluation of loaded chitosan membranes for pain relief and infection prevention

Wounds resulting from surgeries, implantation of medical devices, and musculoskeletal trauma result in pain and can also result in infection of damaged tissue. Up to 80% of these infections are due to biofilm formation either on the surface of implanted devices or on surrounding wounded tissue. Bacteria within a biofilm have intrinsic growth and development characteristics that allow them to withstand up to 1,000 times the minimum inhibitory concentration of antibiotics, demonstrating the need for new therapeutics to prevent and treat these infections. Cis-2-decenoic acid (C2DA) is known to disperse preformed biofilms and can prevent biofilm formation entirely for some strains of bacteria. Additionally, local anesthetics like bupivacaine have been shown to have antimicrobial effects against multiple bacterial strains. This study sought to evaluate hexanoic acid-treated electrospun chitosan membranes (HA-ESCM) as wound dressings that release C2DA and bupivacaine to simultaneously prevent infection and alleviate pain associated with musculoskeletal trauma. Release profiles of both therapeutics were evaluated, and membranes were tested in vitro against Methicillin-resistant Staphylococcus aureus (MRSA) to determine efficacy in preventing biofilm infection and bacterial growth. Results indicate that membranes release both therapeutics for 72 hr, and release profile can be tailored by loading concentration. Membranes were effective in preventing biofilm growth but were toxic to fibroblasts when loaded with 2.5 or 5 mg of bupivacaine.

Beyond Risk: Bacterial Biofilms and Their Regulating Approaches

Bacterial biofilms are complex surface attached communities of bacteria held together by self-produced polymer matrixs mainly composed of polysaccharides, secreted proteins, and extracellular DNAs. Bacterial biofilm formation is a complex process and can be described in five main phases: (i) reversible attachment phase, where bacteria non-specifically attach to surfaces; (ii) irreversible attachment phase, which involves interaction between bacterial cells and a surface using bacterial adhesins such as fimbriae and lipopolysaccharide (LPS); (iii) production of extracellular polymeric substances (EPS) by the resident bacterial cells; (iv) biofilm maturation phase, in which bacterial cells synthesize and release signaling molecules to sense the presence of each other, conducing to the formation of microcolony and maturation of biofilms; and (v) dispersal/detachment phase, where the bacterial cells depart biofilms and comeback to independent planktonic lifestyle. Biofilm formation is detrimental in healthcare, drinking water distribution systems, food, and marine industries, etc. As a result, current studies have been focused toward control and prevention of biofilms. In an effort to get rid of harmful biofilms, various techniques and approaches have been employed that interfere with bacterial attachment, bacterial communication systems (quorum sensing, QS), and biofilm matrixs. Biofilms, however, also offer beneficial roles in a variety of fields including applications in plant protection, bioremediation, wastewater treatment, and corrosion inhibition amongst others. Development of beneficial biofilms can be promoted through manipulation of adhesion surfaces, QS and environmental conditions. This review describes the events involved in bacterial biofilm formation, lists the negative and positive aspects associated with bacterial biofilms, elaborates the main strategies currently used to regulate establishment of harmful bacterial biofilms as well as certain strategies employed to encourage formation of beneficial bacterial biofilms, and highlights the future perspectives of bacterial biofilms.

Methicillin-resistant Staphylococcus aureus (MRSA): antibiotic-resistance and the biofilm phenotype

Staphylococcus aureus (S. aureus) is an asymptomatic colonizer of 30% of all human beings. While generally benign, antibiotic resistance contributes to the success of S. aureus as a human pathogen. Resistance is rapidly evolved through a wide portfolio of mechanisms including horizontal gene transfer and chromosomal mutation. In addition to traditional resistance mechanisms, a special feature of S. aureus pathogenesis is its ability to survive on both biotic and abiotic surfaces in the biofilm state. Due to this characteristic, S. aureus is a leading cause of human infection. Methicillin-resistant S. aureus (MRSA) in particular has emerged as a widespread cause of both community- and hospital-acquired infections. Currently, MRSA is responsible for 10-fold more infections than all multi-drug resistant (MDR) Gram-negative pathogens combined. Recently, MRSA was classified by the World Health Organization (WHO) as one of twelve priority pathogens that threaten human health. In this targeted mini-review, we discuss MRSA biofilm production, the relationship of biofilm production to antibiotic resistance, and front-line techniques to defeat the biofilm-resistance system.

Sodium Oleate Increases Ampicillin Sensitivity in Methylophilus quaylei Biofilms on Teflon and Polypropylene

Background:

Drug combination is a new therapy to improve antibiotic deficiency treatment towards biofilm resistance.

Objective:

This study was conducted to determine the potential effect of sodium oleate to inhibit established biofilms of two strains, methylotrophic bacteria Methylophilus quaylei in combination with ampicillin. Minimum inhibitory concentration (MIC) of ampicillin was determined and added in combination with sodium oleate and examined on planktonic and established biofilms of two strains M. quaylei were characterized by different properties of cell surface hydrophobicity.

Methods:

The effect on biofilms was evaluated by the number of colony forming units (CFUs), crystal violet assay, light and scanning electron microscopy.

Results:

The study demonstrates that sodium oleate has a promoting activity against planktonic growth of M. quaylei strains and has a slight inhibitory effect on biofilm. Addition of sodium oleate enhances the bactericidal effect of ampicillin against biofilm cells. Combination of ampicillin 0.1 mg/ml (MIC) and sodium oleate 0.03 mg/ml showed a remarkable destruction effect on established biofilms.

Discussion:

Combination of ampicillin 0.1 mg/ml (MIC) and sodium oleate 0.03 mg/ml showed a remarkable destruction effect on established biofilms. Overall, results indicated that sodium oleate in combination with ampicillin enhances the inhibition of M. quaylei biofilms and this combination can be utilized for combating bacterial biofilm resistance.

Conclusion:

Overall, results indicated that sodium oleate in combination with ampicillin enhances the inhibition of M. quaylei biofilms and this combination can be utilized for combating bacterial biofilm resistance.

Analysis of antibacterial and antibiofilm activity of purified recombinant Azurin from Pseudomonas aeruginosa

BACKGROUND AND OBJECTIVES

The aim of this study was to evaluate the antibacterial and antibiofilm activity of recombinant Azurin from Pseudomonas aeruginosa against different bacterial species.

MATERIALS AND METHODS

The azurin gene was cloned in the pET21a vector. The pET21a-azurin construct was transformed into Escherichia coli BL21. The recombinant Azurin was expressed and purified using affinity chromatography and confirmed by Western blotting. The cytotoxicity of rAzurin was assessed on peripheral blood mononuclear cells. Antibacterial and antibiofilm activity of rAzurin with different concentrations were determined by micro-broth dilution and crystal violet methods, respectively. The effect of rAzurin on bacterial species was statistically analyzed by t-test and spearman correlation.

RESULTS

The identity of purified protein was confirmed by blotting and distinguished as a 14 kDa band on 15% SDS-PAGE. The IC50 of rAzurin on Peripheral Blood Mononuclear Cell (PBMC) was determined as 377.91±0.5 μg/mL in 24 h. Vibrio cholerae and Campilobacter jejuni displayed the most sensitivity to rAzurin (27.5 and 55 μg/mL, respectively) and the highest resistance (220 μg/mL) was displayed by P. aeruginosa and E. coli. The MIC for other species was 110 μg/mL. The Minimum Biofilm Inhibition Concentration (MBIC) was determined as 220 μg/mL for Salmonella enterica and V. cholerae, 300 μg/mL for Shigella sonnei, Shigella flexneri and P. aeruginosa and 440 μg/mL for the other species. The antimicrobial effect of rAzurin on bacterial species were significant (p value<0.05) and correlation coefficient was negative.

CONCLUSION

The rAzurin appears to be an appropriate choice and a new strategy for prevention of bacterial infection. It inhibits bacterial growth and biofilm formation and candidates as antimicrobial peptides.

In vitro Interactions of Pseudomonas aeruginosa With Scedosporium Species Frequently Associated With Cystic Fibrosis

Members of the Scedosporium apiospermum species complex are the second most frequently isolated pathogens after Aspergillus fumigatus from cystic fibrosis (CF) patients with fungal pulmonary infections. Even so, the main risk factors for the infection are unrevealed. According to previous studies, bacterial infections might reduce the risk of a fungal infection, but an antibacterial therapy may contribute to the airway colonization by several fungal pathogens. Furthermore, corticosteroids, which are often used to reduce lung inflammation in children and adults with CF, are also proved to enhance the growth of A. fumigatus in vitro. Considering all the above discussed points, we aimed to test how Pseudomonas aeruginosa influences the growth of scedosporia and to investigate the potential effect of commonly applied antibacterial agents and corticosteroids on Scedosporium species. Direct interactions between fungal and bacterial strains were tested using the disk inhibition method. Indirect interactions via volatile compounds were investigated by the plate-in-plate method, while the effect of bacterial media-soluble molecules was tested using a modified cellophane assay and also in liquid culture media conditioned by P. aeruginosa. To test the effect of bacterial signal molecules, antibacterial agents and corticosteroids on the fungal growth, the broth microdilution method was used. We also investigated the germination ability of Scedosporium conidia in the presence of pyocyanin and diffusible signal factor by microscopy. According to our results, P. aeruginosa either inhibited or enhanced the growth of scedosporia depending on the culture conditions and the mode of interactions. When the two pathogens were cultured physically separately from each other in the plate-in-plate tests, the presence of the bacteria was able to stimulate the growth of several fungal isolates. While in direct physical contact, bacterial strains inhibited the fungal growth. This effect might be attributed to bacterial signal molecules, which also proved to inhibit the germination and growth of scedosporia. In addition, antibacterial agents showed growth-promoting, while corticosteroids exhibited growth inhibitory effect on several Scedosporium isolates. These data raise the possibility that a P. aeruginosa infection or a previously administered antibacterial therapy might be able to increase the chance of a Scedosporium colonization in a CF lung.

Nonconventional Therapeutics against Staphylococcus aureus

Staphylococcus aureus is one of the most important human pathogens that is responsible for a variety of diseases ranging from skin and soft tissue infections to endocarditis and sepsis. In recent decades, the treatment of staphylococcal infections has become increasingly difficult as the prevalence of multi-drug resistant strains continues to rise. With increasing mortality rates and medical costs associated with drug resistant strains, there is an urgent need for alternative therapeutic options. Many innovative strategies for alternative drug development are being pursued, including disruption of biofilms, inhibition of virulence factor production, bacteriophage-derived antimicrobials, anti-staphylococcal vaccines, and light-based therapies. While many compounds and methods still need further study to determine their feasibility, some are quickly approaching clinical application and may be available in the near future.

Structural and functional studies on Pseudomonas aeruginosa DspI: implications for its role in DSF biosynthesis

DspI, a putative enoyl-coenzyme A (CoA) hydratase/isomerase, was proposed to be involved in the synthesis of cis-2-decenoic acid (CDA), a quorum sensing (QS) signal molecule in the pathogen Pseudomonas aeruginosa (P. aeruginosa). The present study provided a structural basis for the dehydration reaction mechanism of DspI during CDA synthesis. Structural analysis reveals that Glu126, Glu146, Cys127, Cys131 and Cys154 are important for its enzymatic function. Moreover, we show that the deletion of dspI results in a remarkable decreased in the pyoverdine production, flagella-dependent swarming motility, and biofilm dispersion as well as attenuated virulence in P. aeruginosa PA14. This study thus unravels the mechanism of DspI in diffusible signal factor (DSF) CDA biosynthesis, providing vital information for developing inhibitors that interfere with DSF associated pathogenicity in P. aeruginosa.

Unsaturated Fatty Acids Affect Quorum Sensing Communication System and Inhibit Motility and Biofilm Formation of Acinetobacter baumannii

The increasing threat of Acinetobacter baumannii as a nosocomial pathogen is mainly due to the occurrence of multidrug-resistant strains that are associated with the real problem of its eradication from hospital wards. The particular ability of this pathogen to form biofilms contributes to its persistence, increases antibiotic resistance, and promotes persistent/device-related infections. We previously demonstrated that virstatin, which is a small organic compound known to decrease virulence of Vibrio cholera via an inhibition of T4-pili expression, displayed very promising activity to prevent A. baumannii biofilm development. Here, we examined the antibiofilm activity of mono-unsaturated chain fatty acids, palmitoleic (PoA), and myristoleic (MoA) acids, presenting similar action on V. cholerae virulence. We demonstrated that PoA and MoA (at 0.02 mg/mL) were able to decrease A. baumannii ATCC 17978 biofilm formation up to 38% and 24%, respectively, presented a biofilm dispersing effect and drastically reduced motility. We highlighted that these fatty acids decreased the expression of the regulator abaR from the LuxIR-type quorum sensing (QS) communication system AbaIR and consequently reduced the N-acyl-homoserine lactone production (AHL). This effect can be countered by addition of exogenous AHLs. Besides, fatty acids may have additional non-targeted effects, independent from QS. Atomic force microscopy experiments probed indeed that PoA and MoA could also act on the initial adhesion process in modifying the material interface properties. Evaluation of fatty acids effect on 22 clinical isolates showed a strain-dependent antibiofilm activity, which was not correlated to hydrophobicity or pellicle formation ability of the tested strains, and suggested a real diversity in cell-to-cell communication systems involved in A. baumannii biofilm formation.

Advances in the local and targeted delivery of anti-infective agents for management of osteomyelitis

INTRODUCTION

Osteomyelitis, a common and debilitating invasive infection of bone, is a frequent complication following orthopedic surgery and causes pathologic destruction of skeletal tissues. Bone destruction during osteomyelitis results in necrotic tissue, which is poorly penetrated by antibiotics and can serve as a nidus for relapsing infection. Osteomyelitis therefore frequently necessitates surgical debridement procedures, which provide a unique opportunity for targeted delivery of antimicrobial and adjunctive therapies. Areas covered: Following surgical debridement, tissue voids require implanted materials to facilitate the healing process. Antibiotic-loaded, non-biodegradable implants have been the standard of care. However, a new generation of biodegradable, osteoconductive materials are being developed. Additionally, in the face of widespread antimicrobial resistance, alternative therapies to traditional antibiotic regimens are being investigated, including bone targeting compounds, antimicrobial surface modifications of orthopedic implants, and anti-virulence strategies. Expert commentary: Recent advances in biodegradable drug delivery scaffolds make this technology an attractive alternative to traditional techniques for orthopedic infection that require secondary operations for removal. Advances in novel treatment methods are expanding the arsenal of viable antimicrobial treatment strategies in the face of widespread drug resistance. Despite a need for large scale clinical investigations, these strategies offer hope for future treatment of this difficult invasive disease.

Interkingdom signaling in plant-microbe interactions

The widespread communications between prokaryotes and eukaryotes via signaling molecules are believed to affect gene expression in both partners. During the communication process, the contacted organisms produce and release small molecules that establish communication channels between two kingdoms-this procedure is known as interkingdom signaling. Interkingdom communications are widespread between pathogenic or beneficial bacteria and their host plants, with diversified outcomes depending on the specific chemical-triggered signaling pathways. Deciphering the signals or language of this interkingdom communication and uncovering the underlying mechanisms are major current challenges in this field. It is evident that diverse signaling molecules can be produced or derived from bacteria and plants, and researchers have sought to identify these signals and explore the mechanisms of the signaling pathways. The results of such studies will lead to the development of strategies to improve plant disease resistance through controlling interkingdom signals, rather than directly killing the pathogenic bacteria. Also, the identification of signals produced by beneficial bacteria will be useful for agricultural applications. In this review, we summarize the recent progress of cross-kingdom interactions between plant and bacteria, and how LuxR-family transcription factors in plant associated bacterial quorum sensing system are involved in the interkingdom signaling.

Phosphatidylcholine Coatings Deliver Local Antimicrobials and Reduce Infection in a Murine Model: A Preliminary Study

BACKGROUND

Phosphatidylcholine coatings have been shown to elute antibiotics for several days. A recently developed biofilm inhibitor, cis-2-decenoic acid (C2DA), has been shown to exhibit synergistic activity with several common antibiotics. This study aims to evaluate the effectiveness of C2DA and amikacin dual drug delivery from a phosphatidylcholine coating.

QUESTIONS/PURPOSES

(1) What are the in vitro elution profiles of amikacin and C2DA from phosphatidylcholine-coated coupons in incubated phosphate-buffered saline? (2) Does the presence of C2DA in eluate samples lower the amount of amikacin needed for bacterial inhibition in overnight bacterial turbidity assays? (3) Does addition of amikacin and C2DA result in decreased colony-forming units (CFUs) on wire implants and bone when compared with phosphatidylcholine coatings alone in a mouse model of periprosthetic joint infection?

METHODS

Effects of loading concentrations were assessed during 7-day in vitro elution studies for coatings containing all mixtures of 0%, 5%, 15%, and 25% wt of amikacin and C2DA (n = 4) through quantitative high-performance liquid chromatography concentration determination and plotting concentration eluted over time. Antimicrobial activity was assessed by overnight turbidity testing of elution study samples against Staphylococcus aureus or Pseudomonas aeruginosa. In vivo efficacy was assessed using phosphatidylcholine-coated wire implants in a murine (mouse) model of infection (n = 3). Wire implants were coated with phosphatidylcholine containing no antimicrobials, amikacin alone, C2DA alone, or amikacin and C2DA and then inserted into the intramedullary femur of each mouse and inoculated with S aureus. The number of viable bacterial colonies on the implant surface and in the surrounding bone was determined after 1 week with the goal of achieving complete bacterial clearance. Total viable CFU count and proportion of samples achieving complete clearance were compared between groups.

RESULTS

Elution samples showed a burst response of amikacin and C2DA for 1 to 2 days with C2DA release continuing at low levels through Day 4. All tested eluate samples inhibited P aeruginosa. Samples from coatings containing 25% amikacin or 15% amikacin and any amount of C2DA were able to inhibit S aureus formation, but all coatings with 5% amikacin or 15% amikacin but no C2DA were not inhibitory. All in vivo treatment groups achieved complete bacterial clearance on the wire implant, and the C2DA alone and amikacin alone coatings cleared all CFUs in bone (pin: phosphatidylcholine only one of three; amikacin three of three, C2DA three of three, amikacin + C2DA three of three, p = 0.04 [Fisher's exact test]; bone: coating only: zero of three; amikacin: three of three; C2DA; three of three; C2DA + amikacin: one of three; p = 0.03 [Fisher's exact test]).

CONCLUSIONS

Phosphatidylcholine coatings elute antimicrobials in vitro under infinite sink conditions for up to 4 days in phosphate-buffered saline and were able to reduce bacterial colonies in a preliminary in vivo model. Turbidity testing with eluate samples containing varying amounts of C2DA and amikacin agrees with previous studies showing synergy between them.

CLINICAL RELEVANCE

Used as an adjunctive to systemic therapy, C2DA-loaded phosphatidylcholine coatings have potential value as a prophylactic infection prevention measure. Future studies may include different antibiotics, animal studies with larger sample sizes and more controls, and advanced coating delivery methods.

Control of Biofilm Formation: Antibiotics and Beyond

Biofilm-associated bacteria are less sensitive to antibiotics than free-living (planktonic) cells. Furthermore, with variations in the concentration of antibiotics throughout a biofilm, microbial cells are often exposed to levels below inhibitory concentrations and may develop resistance. This, as well as the irresponsible use of antibiotics, leads to the selection of pathogens that are difficult to eradicate. The Centers for Disease Control and Prevention use the terms "antibiotic" and "antimicrobial agent" interchangeably. However, a clear distinction between these two terms is required for the purpose of this assessment. Therefore, we define "antibiotics" as pharmaceutically formulated and medically administered substances and "antimicrobials" as a broad category of substances which are not regulated as drugs. This comprehensive minireview evaluates the effect of natural antimicrobials on pathogens in biofilms when used instead of, or in combination with, commonly prescribed antibiotics.

In vitro evaluation of antibacterial activity of phytochemicals and micronutrients against Borrelia burgdorferi and Borrelia garinii

Aims

Little is known about the effects of phytochemicals against Borrelia sp. causing Lyme disease. Current therapeutic approach to this disease is limited to antibiotics. This study examined the anti‐borreliae efficacy of several plant‐derived compounds and micronutrients.

Methods and Results

We tested the efficacy of 15 phytochemicals and micronutrients against three morphological forms of Borrelia burgdoferi and Borrelia garinii: spirochetes, latent rounded forms and biofilm. The results showed that the most potent substances against the spirochete and rounded forms of B. burgdorferi and B. garinii were cis‐2‐decenoic acid, baicalein, monolaurin and kelp (iodine); whereas, only baicalein and monolaurin revealed significant activity against the biofilm. Moreover, cis‐2‐decenoic acid, baicalein and monolaurin did not cause statistically significant cytotoxicity to human HepG2 cells up to 125 μg ml⁻¹ and kelp up to 20 μg ml⁻¹.

Conclusions

The most effective antimicrobial compounds against all morphological forms of the two tested Borrelia sp. were baicalein and monolaurin. This might indicate that the presence of fatty acid and phenyl groups is important for comprehensive antibacterial activity.

Significance and Impact of the Study

This study reveals the potential of phytochemicals as an important tool in the fight against the species of Borrelia causing Lyme disease.

Recent advances in thromboresistant and antimicrobial polymers for biomedical applications: just say yes to nitric oxide (NO)

Biomedical devices are essential for patient diagnosis and treatment; however, when blood comes in contact with foreign surfaces or homeostasis is disrupted, complications including thrombus formation and bacterial infections can interrupt device functionality, causing false readings and/or shorten device lifetime. Here, we review some of the current approaches for developing antithrombotic and antibacterial materials for biomedical applications. Special emphasis is given to materials that release or generate low levels of nitric oxide (NO). Nitric oxide is an endogenous gas molecule that can inhibit platelet activation as well as bacterial proliferation and adhesion. Various NO delivery vehicles have been developed to improve NO's therapeutic potential. In this review, we provide a summary of the NO releasing and NO generating polymeric materials developed to date, with a focus on the chemistry of different NO donors, the polymer preparation processes, and in vitro and in vivo applications of the two most promising types of NO donors studied thus far, N-diazeniumdiolates (NONOates) and S-nitrosothiols (RSNOs).

Antibiotic-loaded phosphatidylcholine inhibits staphylococcal bone infection

AIM: To test antibiotic-loaded coating for efficacy in reducing bacterial biofilm and development of osteomyelitis in an orthopaedic model of implant infection.

METHODS: Phosphatidylcholine coatings loaded with 25% vancomycin were applied to washed and sterilized titanium wires 20 mm in length. A 10 mm segment was removed from rabbit radius (total = 9; 5 coated, 4 uncoated), and the segment was injected with 1 × 10⁶ colony forming units (CFUs) of Staphylococcus aureus (UAMS-1 strain). Titanium wires were inserted through the intramedullary canal of the removed segment and into the proximal radial segment and the segment was placed back into the defect. After 7 d, limbs were removed, X-rayed, swabbed for tissue contamination. Wires were removed and processed to determine attached CFUs. Tissue was swabbed and streaked on agar plates to determine bacteriological score.

RESULTS: Antibiotic-loaded coatings resulted in significantly reduced biofilm formation (4.7 fold reduction in CFUs; P < 0.001) on titanium wires and reduced bacteriological score in surrounding tissue (4.0 ± 0 for uncoated, 1.25 ± 0.5 for coated; P = 0.01). Swelling and pus formation was evident in uncoated controls at the 7 d time point both visually and radiographically, but not in antibiotic-loaded coatings.

CONCLUSION: Active antibiotic was released from coated implants and significantly reduced signs of osteomyelitic symptoms. Implant coatings were well tolerated in bone. Further studies with additional control groups and longer time periods are warranted. Antibiotic-loaded phosphatidylcholine coatings applied at the point of care could prevent implant-associated infection in orthopaedic defects.

Interaction of Staphylococcus aureus persister cells with the host when in a persister state and following awakening

Persister cells, a tolerant cell sub-population, are commonly associated with chronic and recurrent infections. However, little is known about their ability to actually initiate or establish an infection, become virulent and cause pathogenicity within a host. Here we investigated whether Staphylococcus aureus persister cells initiate an infection and are recognized by macrophages, while in a persister cell status, and upon awakening due to exposure to cis-2-decenoic acid (cis-DA). Our results show that S. aureus persister cells are not able to initiate infections in A. thaliana and present significantly reduced virulence towards C. elegans compared to total populations. In contrast, awakened S. aureus persister cells are able to initiate infections in A. thaliana and in C. elegans albeit, with lower mortality than total population. Furthermore, exposure of S. aureus persister cells to cis-DA led to a loss of tolerance to ciprofloxacin, and an increase of the bacterial fluorescence to levels found in total population. In addition, macrophage engulfment of persister cells was significantly lower than engulfment of total population, both before and following awakening. Overall our findings indicate that upon awakening of a persister population the cells regain their ability to infect hosts despite the absence of an increased immune response.

Agents that inhibit bacterial biofilm formation

In the biofilm form, bacteria are more resistant to various antimicrobial treatments. Bacteria in a biofilm can also survive harsh conditions and withstand the host's immune system. Therefore, there is a need for new treatment options to treat biofilm-associated infections. Currently, research is focused on the development of antibiofilm agents that are nontoxic, as it is believed that such molecules will not lead to future drug resistance. In this review, we discuss recent discoveries of antibiofilm agents and different approaches to inhibit/disperse biofilms. These new antibiofilm agents, which contain moieties such as imidazole, phenols, indole, triazole, sulfide, furanone, bromopyrrole, peptides, etc. have the potential to disperse bacterial biofilms in vivo and could positively impact human medicine in the future.

Control of Biofilms with the Fatty Acid Signaling Molecule cis-2-Decenoic Acid

Biofilms are complex communities of microorganisms in organized structures attached to surfaces. Importantly, biofilms are a major cause of bacterial infections in humans, and remain one of the most significant challenges to modern medical practice. Unfortunately, conventional therapies have shown to be inadequate in the treatment of most chronic biofilm infections based on the extraordinary innate tolerance of biofilms to antibiotics. Antagonists of quorum sensing signaling molecules have been used as means to control biofilms. QS and other cell-cell communication molecules are able to revert biofilm tolerance, prevent biofilm formation and disrupt fully developed biofilms, albeit with restricted effectiveness. Recently however, it has been demonstrated that Pseudomonas aeruginosa produces a small messenger molecule cis-2-decenoic acid (cis-DA) that shows significant promise as an effective adjunctive to antimicrobial treatment of biofilms. This molecule is responsible for induction of the native biofilm dispersion response in a range of Gram-negative and Gram-positive bacteria and in yeast, and has been shown to reverse persistence, increase microbial metabolic activity and significantly enhance the cidal effects of conventional antimicrobial agents. In this manuscript, the use of cis-2-decenoic acid as a novel agent for biofilm control is discussed. Stimulating the biofilm dispersion response as a novel antimicrobial strategy holds significant promise for enhanced treatment of infections and in the prevention of biofilm formation.

Prevention and treatment of Staphylococcus aureus biofilms

S. aureus colonizes both artificial and tissue surfaces in humans causing chronic persistent infections that are difficult to cure. It is a notorious pathogen due to its antibiotic recalcitrance and phenotypic adaptability, both of which are facilitated by its ability to develop biofilms. S. aureus biofilms challenge conventional anti-infective approaches, most notably antibiotic therapy. Therefore there is an unmet need to develop and include parallel approaches that target S. aureus biofilm infections. This review discusses two broad anti-infective strategies: (1) preventative approaches (anti-biofilm surface coatings, the inclusion of biofilm-specific vaccine antigens); and (2) approaches aimed at eradicating established S. aureus biofilms, particularly those associated with implant infections. Advances in understanding the distinct nature of S. aureus biofilm development and pathogenesis have led to growing optimism in S. aureus biofilm targeted anti-infective strategies. Further research is needed however, to see the successful administration and validation of these approaches to the diverse types of infections caused by S. aureus biofilms from multiple clinical strains.

A combination of cis-2-decenoic acid and chlorhexidine removes dental plaque

OBJECTIVES

To investigate the ability of cis-2-decenoic acid (C2DA) to induce dispersion in single-species biofilms formed by Streptococcus mutans and Candida albicans, as well as to remove their bacterial-fungal dual-species biofilms when combined with low concentrations of chlorhexidine (CHX).

METHODS

For biofilm dispersal bioassays, single-species biofilms of S. mutans and C. albicans were grown on the inside surface of petri dishes, using a semi-batch culture method in which the medium was replaced every 24h for 5 days. Biofilms were then treated with very low concentrations of C2DA (100 and 310 nM) for 1h to release cells into the bulk liquid and to evaluate dispersed cell number by measuring the optical density (OD). To assess the ability of C2DA combined CHX treatments to remove tested microorganisms' dual-species biofilms, they were grown on saliva-coated hydroxyapatite (sHA) discs for 48 h and then were treated with three different concentrations of CHX (0.08%, 0.06% and 0.04%) alone or in combination with indicated concentrations of C2DA for 1 min twice daily for 3 subsequent days. Biofilms were then either subjected to the field emission scanning electron microscopy (FESEM) analysis or harvested and colony forming units (CFUs) were counted after plating on agar.

RESULTS

Treatment of pre-established biofilms with 310 nM C2DA caused an approximately two-fold increase in the number of planktonic cells in both cultures. A combination of 310 nM C2DA and 0.04% CHX resulted in significant removal (p-value <0.05) of dual-species biofilms from sHA discs surface.

CONCLUSIONS

Anti-biofilm characteristic of C2DA boosts the action of CHX even at low concentrations.

The DSF Family of Cell-Cell Signals: An Expanding Class of Bacterial Virulence Regulators

Many pathogenic bacteria use cell–cell signaling systems involving the synthesis and perception of diffusible signal molecules to control virulence as a response to cell density or confinement to niches. Bacteria produce signals of diverse structural classes. Signal molecules of the diffusible signal factor (DSF) family are cis-2-unsaturated fatty acids. The paradigm is cis-11-methyl-2-dodecenoic acid from Xanthomonas campestris pv. campestris (Xcc), which controls virulence in this plant pathogen. Although DSF synthesis was thought to be restricted to the xanthomonads, it is now known that structurally related molecules are produced by the unrelated bacteria Burkholderia cenocepacia and Pseudomonas aeruginosa. Furthermore, signaling involving these DSF family members contributes to bacterial virulence, formation of biofilms and antibiotic tolerance in these important human pathogens. Here we review the recent advances in understanding DSF signaling and its regulatory role in different bacteria. These advances include the description of the pathway/mechanism of DSF biosynthesis, identification of novel DSF synthases and new members of the DSF family, the demonstration of a diversity of DSF sensors to include proteins with a Per-Arnt-Sim (PAS) domain and the description of some of the signal transduction mechanisms that impinge on virulence factor expression. In addition, we address the role of DSF family signals in interspecies signaling that modulates the behavior of other microorganisms. Finally, we consider a number of recently reported approaches for the control of bacterial virulence through the modulation of DSF signaling.

Biofilms in periprosthetic orthopedic infections

As the number of total joint arthroplasty and internal fixation procedures continues to rise, the threat of infection following surgery has significant clinical implications. These infections may have highly morbid consequences to patients, who often endure additional surgeries and lengthy exposures to systemic antibiotics, neither of which are guaranteed to resolve the infection. Of particular concern is the threat of bacterial biofilm development, since biofilm-mediated infections are difficult to diagnose and effective treatments are lacking. Developing therapeutic strategies have targeted mechanisms of biofilm formation and the means by which these bacteria communicate with each other to take on specialized roles such as persister cells within the biofilm. In addition, prevention of infection through novel coatings for prostheses and the local delivery of high concentrations of antibiotics by absorbable carriers has shown promise in laboratory and animal studies. Biofilm development, especially in an arthoplasty environment, and future diagnostic and treatment options are discussed.

Transcriptome analysis of the biofilm formed by methicillin-susceptible Staphylococcus aureus

Biofilm formation is regarded as one of the major determinants in the prevalence of methicillin-resistant Staphylococcus aureus (MRSA) as pathogens of medical device-related infection. However, methicillin-susceptible S. aureus (MSSA) can also form biofilm in vitro and such biofilms are resistant to vancomycin. Hence, researching the possible mechanisms of MSSA biofilm formation is urgent and necessary. Here, we used S. aureus ATCC25923 as the model strain, and studied gene expression profiles in biofilms after the treatment of ursolic acid and resveratrol using RNA-seq technology. The results showed that only ursolic acid could inhibit biofilm formation, which differed from their applied on the multiple clinical drugs resistant MRSA biofilm. RNA-seq data was validated by examining the expression of six genes involved in biofilm formation by qRT-PCR. These data analysis indicated that the mechanism of the MSSA biofilm formation was different from that of the MRSA, due to absence of accessory gene regulator (agr) function. These findings suggest that biofilms of S. aureus with agr dysfunction may be more resistant than those with agr function. Therefore, the infection from clinical MSSA may be recalcitrant once forming biofilm. Further study is necessary to uncover the mechanisms of biofilm formation in other clinical S. aureus.

Novel Antibiotic-loaded Point-of-care Implant Coating Inhibits Biofilm

BACKGROUND

Orthopaedic biomaterials are susceptible to biofilm formation. A novel lipid-based material has been developed that may be loaded with antibiotics and applied as an implant coating at point of care. However, this material has not been evaluated for antibiotic elution, biofilm inhibition, or in vivo efficacy.

QUESTIONS/PURPOSES

(1) Do antibiotic-loaded coatings inhibit biofilm formation? (2) Is the coating effective in preventing biofilm in vivo?

METHODS

Purified phosphatidylcholine was mixed with 25% amikacin or vancomycin or a combination of 12.5% of both. A 7-day elution study for coated titanium and stainless steel coupons was followed by turbidity and zone of inhibition assays against Staphylococcus aureus and Pseudomonas aeruginosa. Coupons were inoculated with bacteria and incubated 24 hours (N = 4 for each test group). Microscopic images of biofilm were obtained. After washing and vortexing, attached bacteria were counted. A mouse biofilm model was modified to include coated and uncoated stainless steel wires inserted into the lumens of catheters inoculated with a mixture of S aureus or P aeruginosa. Colony-forming unit counts (N = 10) and scanning electron microscopy imaging of implants were used to determine antimicrobial activity.

RESULTS

Active antibiotics with colony inhibition effects were eluted for up to 6 days. Antibiotic-loaded coatings inhibited biofilm formation on in vitro coupons (log-fold reductions of 4.3 ± 0.4 in S aureus and 3.1 ± 0 for P aeruginosa in phosphatidylcholine-only coatings, 5.6 ± 0 for S aureus and 3.1 ± 0 for P aeruginosa for combination-loaded coatings, 5.5 ± 0.3 for S aureus in vancomycin-loaded coatings, and 3.1 ± 0 for P aeruginosa for amikacin-loaded coatings (p < 0.001 for all comparisons of antibiotic-loaded coatings against uncoated controls for both bacterial strains, p < 0.001 for comparison of antibiotic-loaded coatings against phosphatidylcholine only for S aureus, p = 0.54 for comparison of vancomycin versus combination coating in S aureus, P = 0.99 for comparison of antibiotic- and unloaded phosphatidylcholine coatings in P aeruginosa). Similarly, antibiotic-loaded coatings reduced attachment of bacteria to wires in vivo (log-fold reduction of 2.54 ± 0; p < 0.001 for S aureus and 0.83 ± 0.3; p = 0.112 for P aeruginosa).

CONCLUSIONS

Coatings deliver active antibiotics locally to inhibit biofilm formation and bacterial growth in vivo. Future evaluations will include orthopaedic preclinical models to confirm therapeutic efficacy.

CLINICAL RELEVANCE

Clinical applications of local drug delivery coating could reduce the rate of implant-associated infections.

Dissection of the cis-2-decenoic acid signaling network in Pseudomonas aeruginosa using microarray technique

Many bacterial pathogens use quorum-sensing (QS) signaling to regulate the expression of factors contributing to virulence and persistence. Bacteria produce signals of different chemical classes. The signal molecule, known as diffusible signal factor (DSF), is a cis-unsaturated fatty acid that was first described in the plant pathogen Xanthomonas campestris. Previous works have shown that human pathogen, Pseudomonas aeruginosa, also synthesizes a structurally related molecule, characterized as cis-2-decenoic acid (C₁₀: Δ², CDA) that induces biofilm dispersal by multiple types of bacteria. Furthermore, CDA has been shown to be involved in inter-kingdom signaling that modulates fungal behavior. Therefore, an understanding of its signaling mechanism could suggest strategies for interference, with consequences for disease control. To identify the components of CDA signaling pathway in this pathogen, a comparative transcritpome analysis was conducted, in the presence and absence of CDA. A protein-protein interaction (PPI) network for differentially expressed (DE) genes with known function was then constructed by STRING and Cytoscape. In addition, the effects of CDA in combination with antimicrobial agents on the biofilm surface area and bacteria viability were evaluated using fluorescence microscopy and digital image analysis. Microarray analysis identified 666 differentially expressed genes in the presence of CDA and gene ontology (GO) analysis revealed that in P. aeruginosa, CDA mediates dispersion of biofilms through signaling pathways, including enhanced motility, metabolic activity, virulence as well as persistence at different temperatures. PPI data suggested that a cluster of five genes (PA4978, PA4979, PA4980, PA4982, PA4983) is involved in the CDA synthesis and perception. Combined treatments using both CDA and antimicrobial agents showed that following exposure of the biofilms to CDA, remaining cells on the surface were easily removed and killed by antimicrobials.