Biofilms in infections of the eye

Anti-Staphylococcal Biofilm Effects of a Liposome-Based Formulation Containing Citrus Polyphenols

Biofilms are surface-associated microbial communities embedded in a matrix that is almost impenetrable to antibiotics, thus constituting a critical health threat. Biofilm formation on the cornea or ocular devices can lead to serious and difficult-to-treat infections. Nowadays, natural molecules with antimicrobial activity and liposome-based delivery systems are proposed as anti-biofilm candidates. In this study, the anti-biofilm activity of a formulation containing citrus polyphenols encapsulated in liposomes was evaluated against Staphylococcus aureus and Staphylococcus epidermidis, the most common agents in ocular infections. The formulation activity against planktonic staphylococci was tested by broth microdilution and sub-inhibitory concentrations were used to evaluate the effect on biofilm formation using the crystal violet (CV) assay. The eradicating effect of the preparation on mature biofilms was investigated by the CV assay, plate count, and confocal laser scanning microscopy. The product was bactericidal against staphylococci at a dilution of 1:2 or 1:4 and able to reduce biofilm formation even if diluted at 1:64. The formulation also had the ability to reduce the biomass of mature biofilms without affecting the number of cells, suggesting activity on the extracellular matrix. Overall, our results support the application of the used liposome-encapsulated polyphenols as an anti-biofilm strategy to counter biofilm-associated ocular infections.

Bacteria-Targeting Nanoparticles with ROS-Responsive Antibiotic Release to Eradicate Biofilms and Drug-Resistant Bacteria in Endophthalmitis

Background

Bacterial endophthalmitis is an acute progressive visual threatening disease and one of the most important causes of blindness worldwide. Current treatments are unsatisfactory due to the emergence of drug-resistant bacteria and the formation of biofilm.

Purpose

The aim of our research was to construct a novel nano-delivery system with better antimicrobial and antibiofilm effects.

Methods

This study developed a novel antibiotic nanoparticle delivery system (MXF@UiO-UBI-PEGTK), which is composed of (i) moxifloxacin (MXF)-loaded UiO-66 nanoparticle as the core, (ii) bacteria-targeting peptide ubiquicidin (UBI29-41) immobilized on UiO-66, and (iii) ROS-responsive poly (ethylene glycol)-thioketal (PEG-TK) as the surface shell. Then the important properties of the newly developed delivery system, including biocompatibility, toxicity, release percentage, thermal stability, ability of targeting bacteria, and synergistic antibacterial effects on bacterial biofilms and endophthalmitis, were evaluated.

Results

In vitro, MXF@UiO-UBI-PEGTK exhibited significant antibiotic effects including the excellent antibiofilm property against Staphylococcus aureus, Pseudomonas aeruginosa, and methicillin-resistant Staphylococcus aureus at high levels of ROS. Moreover, MXF@UiO-UBI-PEGTK demonstrated outstanding efficacy in treating bacterial endophthalmitis in vivo.

Conclusion

This novel nanoparticle delivery system with ROS-responsive and bacteria-targeted properties promotes the precise and effective release of drugs and has significant potential for clinical application of treating bacterial endophthalmitis.

A review on antimicrobial strategies in mitigating biofilm-associated infections on medical implants

Biomedical implants are crucial in providing support and functionality to patients with missing or defective body parts. However, implants carry an inherent risk of bacterial infections that are biofilm-associated and lead to significant complications. These infections often result in implant failure, requiring replacement by surgical restoration. Given these complications, it is crucial to study the biofilm formation mechanism on various biomedical implants that will help prevent implant failures. Therefore, this comprehensive review explores various types of implants (e.g., dental implant, orthopedic implant, tracheal stent, breast implant, central venous catheter, cochlear implant, urinary catheter, intraocular lens, and heart valve) and medical devices (hemodialyzer and pacemaker) in use. In addition, the mechanism of biofilm formation on those implants, and their pathogenesis were discussed. Furthermore, this article critically reviews various approaches in combating implant-associated infections, with a special emphasis on novel non-antibiotic alternatives to mitigate biofilm infections.

Characteristics of Bacterial Biofilm Formation in Nasolacrimal Silicone Tubes Post-dacryocystorhinostomy

PURPOSE

To examine the biofilm formation characteristics of bacteria identified at the genus level in samples obtained from silicone tubes after dacryocystorhinostomy surgery.

METHODS

In the study involving consecutive patients who underwent dacryocystorhinostomy surgery at Ankara Bilkent City Hospital and whose silicone tubes were removed six months after surgery, between January 2023 and May 2023; the tubes were placed in glycerol-PBS (phosphate buffered saline) solution and cultured on descriptive selective media at the genus level. The biofilm-forming properties of the obtained isolates were examined in solid-air and liquid-air interphases. Salmonella Typhimurium ATCC SL1344 strain was used as the control bacterium.

RESULTS

As a result of the analysis of the samples taken from the patients, Pseudomonas spp. was identified in three of the samples, Staphylococcus spp. in five of the samples, and Streptococcus spp. in one of the samples. Among these samples, except for the bacteria identified in samples one and five, the rest were found to be strong biofilm producers. In all strong biofilm producers, the maximum biofilm production time was determined as 72 h and the incubation temperature was 37°C. The presence of cellulose and amyloid proteins in biofilm matrix structures is identified. Swimming and swarming motilities were observed in all bacterial samples.

CONCLUSION

Since biofilms are considered potential factors in the pathogenesis of infectious and inflammatory diseases, they are a subject that needs to be thoroughly investigated. In our study, although there were no clinical infections in any of the patients, biofilm formation was detected in the patient samples. The fact that the bacteria exhibited moderate to strong biofilm formation characteristics suggests that these microorganisms could be persistent infectious agents.

Antimicrobial effect of chamomile-containing over-the-counter ear and eye drops

Chamomile (Matricaria chamomilla) is a plant with known antimicrobial, anti-inflammatory, and analgesic properties. Homeopathic drops containing chamomile extract are often used for ear pain and chronic ear infections. We aimed to evaluate the antimicrobial effect of over-the-counter eardrops containing chamomile against organisms causing bacterial conjunctivitis and otitis externa. Liquid cultures of Streptococcus aureus and Pseudomonas aeruginosa were exposed to increasing concentrations of eardrops containing chamomile extract. Liquid cultures of S. aureus and Streptococcus pneumoniae were exposed to increasing concentrations of chamomile eye drops for 5, 10, 15, and 45 min. Colony forming units (CFUs) were assessed after 18 h. Viability assays for these organisms were performed using the resazurin microdilution assay. We observed a reduction in the number of P. aeruginosa CFUs when the bacteria were exposed to any of the three concentrations of the chamomile drops as early as 5 min, with maximal reduction upon exposure to the 30% concentration at 45 min. Reduction in S. aureus CFUs, on the other hand, was observed for all three concentrations as maximal in the 5 min of exposure. We observed a marked reduction in the number of S. aureus CFUs upon exposure to any of the three preparations of chamomile-containing eye drops, which was almost immediate at 10% concentration. Streptococcus pneumoniae reduction happened at 5 min and continued through the 45-min observation period for all three concentrations. Our findings suggest that over-the-counter ear drops containing chamomile extract could potentially be used as a non-prescription treatment for mild cases of otitis externa and bacterial conjunctivitis.

Quantifying the Dynamics of Bacterial Biofilm Formation on the Surface of Soft Contact Lens Materials Using Digital Holographic Tomography to Advance Biofilm Research

The increase in bacterial resistance to antibiotics in recent years demands innovative strategies for the detection and combating of biofilms, which are notoriously resilient. Biofilms, particularly those on contact lenses, can lead to biofilm-related infections (e.g., conjunctivitis and keratitis), posing a significant risk to patients. Non-destructive and non-contact sensing techniques are essential in addressing this threat. Digital holographic tomography emerges as a promising solution. This allows for the 3D reconstruction of the refractive index distribution in biological samples, enabling label-free visualization and the quantitative analysis of biofilms. This tool provides insight into the dynamics of biofilm formation and maturation on the surface of transparent materials. Applying digital holographic tomography for biofilm examination has the potential to advance our ability to combat the antibiotic bacterial resistance crisis. A recent study focused on characterizing biofilm formation and maturation on six soft contact lens materials (three silicone hydrogels, three hydrogels), with a particular emphasis on Staphylococcus epidermis and Pseudomonas aeruginosa, both common culprits in ocular infections. The results revealed species- and time-dependent variations in the refractive indexes and volumes of biofilms, shedding light on cell dynamics, cell death, and contact lens material-related factors. The use of digital holographic tomography enables the quantitative analysis of biofilm dynamics, providing us with a better understanding and characterization of bacterial biofilms.

Hydroquinine Enhances the Efficacy of Contact Lens Solutions for Inhibiting Pseudomonas aeruginosa Adhesion and Biofilm Formation

P. aeruginosa is one of the most common bacteria causing contact lens-related microbial keratitis (CLMK). Previous studies report that disinfecting solutions were ineffective in preventing biofilm formation. Solutions containing novel natural agents may be an excellent alternative for reducing the risk of CLMK. Here, we investigate the disinfecting properties of hydroquinine in combination with multipurpose solutions (MPSs) to prevent P. aeruginosa adhesion and biofilm formation. We examined the antibacterial, anti-adhesion, and anti-biofilm properties of hydroquinine-formulated MPSs compared to MPSs alone. Using RT-qPCR, hydroquinine directly affected the expression levels of adhesion-related genes, namely, cgrC, cheY, cheZ, fimU, and pilV, resulting in reduced adhesion and anti-biofilm formation. Using ISO 14729 stand-alone testing, hydroquinine met the criteria (>99.9% killing at disinfection time) against both P. aeruginosa reference and clinical strains. Using the crystal violet retention assay and FE-SEM, MPSs combined with hydroquinine were effective in inhibiting P. aeruginosa adhesion and destroying preexisting biofilms. This report is the first to highlight the potential utility of hydroquinine-containing formulations as a disinfecting solution for contact lenses, specifically for inhibiting adhesion and destroying biofilm. These findings may aid in the development of novel disinfectants aimed at combating P. aeruginosa, thereby potentially reducing the incidence of CLMK.

Evaluation of combined carbon dots and ciprofloxacin on the expression level of pslA, pelA, and ppyR genes and biofilm production in ciprofloxacin-resistant Pseudomonas aeruginosa isolates from burn wound infection in Iran

OBJECTIVES

Antimicrobial resistance and biofilm formation are increasingly significant public health concerns. This study aimed to examine the antibacterial and antibiofilm properties of carbon dots (C-dots) alone and in combination with antibiotics against biofilm-forming isolates of Pseudomonas aeruginosa.

METHODS

The antibacterial property of C-dots was investigated by broth microdilution method against ATCC PAO1 and P. aeruginosa clinical isolates. The antibacterial effect of the C-dots and ciprofloxacin combination was investigated using the checkerboard method. The antibiofilm effect of the C-dots alone and its combination with ciprofloxacin was evaluated using the microtiter plate method. Subsequently, the toxicity of each agent was tested on L929 fibroblast cells. In the end, the effects of C-dots on the expression levels of pslA, pelA, and ppyR genes were determined using real-time quantitative PCR.

RESULTS

The combination of C-dots and ciprofloxacin exhibited a synergistic effect. Additionally, this compound substantially decreased bacterial growth (P < 0.0001) and inhibited biofilm formation at MIC (96 µg/mL) and sub-MIC (48 µg/mL) concentrations (P < 0.0053, P < 0.01). After being exposed to C-dots at a concentration of 1mg/mL for 24 hours, the survival rate of L929 cells was 87.3%. The expression of genes pslA, pelA, and ppyR, associated with biofilm formation in P. aeruginosa, was significantly reduced upon exposure to C-dots (P < 0.0023).

CONCLUSIONS

The findings demonstrate a promising new treatment method for infections. Furthermore, reducing the dosage of antibiotics can lead to an improvement in the toxic effects caused by dose-dependent antibiotics and antimicrobial activity.

Comparative outcomes of the pathogen in cultured Jones tubes used in lacrimal bypass surgery according to follow up periods

AIM

To evaluate the pathogens in cultured Jones tubes used in lacrimal bypass surgery according to the postoperative periods and to obtain data for the prevention of infection of functional lacrimal stent invention.

METHODS

Totally 71 patients (81 eyes) who underwent the removal of Jones tubes were enrolled in study. All the removed Jones tubes were cultured for bacterial and fungal identification and tested for bacterial antibiotic sensitivity. The results were analyzed according to the duration of the inserted Jones tube after lacrimal bypass surgery.

RESULTS

Of the 81 eyes, bacteria were isolated from 69 eyes (85.2%) and fungi from 6 eyes (7.4%). Among 69 eyes, 40.6% showed Staphylococcus aureus (S. aureus), 11.6% were Pseudomonas aeruginosa (P. aeruginosa). Gram-positive bacteria were isolated more than Gram-negative bacteria, but Gram-negative bacteria showed a higher incidence in the Jones tube implanted for over 10y (P=0.035). The antibiotic sensitivity test showed that 46.4% of S. aureus were resistant to oxacillin. In terms of antibiotics commonly used in ocular clinical practice, vancomycin was sensitive to S. aureus and Streptococcus pneumoniae (S. pneumoniae), amikacin responded to P. aeruginosa and Proteus mirabilis (P. mirabilis). Trimethoprim/sulfamethoxazole (TMP/SMX) was all sensitive to S. aureus, S. pneumoniae and P. mirabilis except P. aeruginosa.

CONCLUSION

S. aureus is the most commonly found organism in the Jones tube after lacrimal bypass surgery, and 46.4% of them are methicillin-resistant S. aureus (MRSA), sensitive to vancomycin. Especially, P. mirabilis responded with amikacin is dominantly detected in the Jones tubes implanted for more than 10y.

Microbial Biofilms: Applications, Clinical Consequences, and Alternative Therapies

Biofilms are complex communities of microorganisms that grow on surfaces and are embedded in a matrix of extracellular polymeric substances. These are prevalent in various natural and man-made environments, ranging from industrial settings to medical devices, where they can have both positive and negative impacts. This review explores the diverse applications of microbial biofilms, their clinical consequences, and alternative therapies targeting these resilient structures. We have discussed beneficial applications of microbial biofilms, including their role in wastewater treatment, bioremediation, food industries, agriculture, and biotechnology. Additionally, we have highlighted the mechanisms of biofilm formation and clinical consequences of biofilms in the context of human health. We have also focused on the association of biofilms with antibiotic resistance, chronic infections, and medical device-related infections. To overcome these challenges, alternative therapeutic strategies are explored. The review examines the potential of various antimicrobial agents, such as antimicrobial peptides, quorum-sensing inhibitors, phytoextracts, and nanoparticles, in targeting biofilms. Furthermore, we highlight the future directions for research in this area and the potential of phytotherapy for the prevention and treatment of biofilm-related infections in clinical settings.

An All-in-One Highly Multiplexed Diagnostic Assay for Rapid, Sensitive, and Comprehensive Detection of Intraocular Pathogens

PURPOSE

Intraocular infections are sight-threatening conditions that can lead to vision loss. Rapid identification of the etiologies plays a key role in early initiation of effective therapy to save vision. However, current diagnostic modalities are time consuming and lack sensitivity and inclusiveness. We present here a newly developed comprehensive ocular panel designed to improve diagnostic yields and provide a tool for rapid and sensitive pathogen detection.

DESIGN

Experimental laboratory investigation.

METHODS

A panel containing 46 pathogens and 2 resistance/virulence markers that are commonly detected in intraocular infections was developed. Genomic targets were scrutinized for stretches predicted to be specific for a particular species while being conserved across different strains. A set of primers for sample enrichment, and two 50mer NanoString compatible probes were then designed for each target. Probe-target hybrids were detected and quantified using the NanoString nCounter SPRINT Profiler. Diagnostic feasibility was assessed in a pilot clinical study testing samples from infectious retinitis (n = 15) and endophthalmitis (n = 12) patients, for which the etiologies were confirmed by polymerase chain reaction (PCR) or culture.

RESULTS

Analytical studies demonstrated highly sensitive detection of a broad spectrum of pathogens, including bacteria, viruses, and parasites, with limits of detection being as low as 2.5 femtograms per reaction. We also found excellent target specificity, with minimal cross-reactivity detected. The custom-designed NanoString ocular panel correctly identified the causative agent from all clinical specimens positive for a variety of pathogens.

CONCLUSION

This highly multiplexed panel for pathogen detection offers a sensitive, comprehensive, and uniform assay run directly on ocular fluids that could significantly improve diagnostics of sight-threatening intraocular infections.

Insights into the physical and chemical properties of struvite crystal surfaces in terms of the effectiveness of bacterial adhesion

In this paper, we present the results of research on the physicochemical properties of two selected faces of the struvite crystal, which is the main component of infectious urinary stones. Two main faces, (001) and ([Formula: see text]), ending the c-axis, were selected for the study. These faces are not related by symmetry relations, which means, among other things, that they should have a different atomic structure, which was confirmed experimentally. In addition, the studies show that the tested surfaces have hydrophilic properties, however, the ([Formula: see text]) face is more hydrophilic compared to the (001) face. The physicochemical properties of the crystal as a whole, as well as the physicochemical properties of these faces influence the magnitude of adhesion. The adhesive force in both water and artificial urine is greater for face ([Formula: see text]) compared to face (001). The assessment of the adhesion of Proteus mirabilis bacteria in artificial urine also shows that the adhesion is greater for face ([Formula: see text]) than for face (001). The adhesion of bacteria to the examined faces of the struvite crystal, and in particular the increased adhesion of bacteria to the face ([Formula: see text]), may be the first stage of biofilm formation, which may result in a high rate of recurrence of infectious urinary stones after treatment.

Atypical microbial keratitis

Atypical microbial keratitis refers to corneal infections caused by micro-organisms not commonly encountered in clinical practice. Unlike infections caused by common bacteria, cases of atypical microbial keratitis are often associated with worse clinical outcomes and visual prognosis. This is due to the challenges in the identification of causative organisms with standard diagnostic techniques, resulting in delays in the initiation of appropriate therapies. Furthermore, due to the comparatively lower incidence of atypical microbial keratitis, there is limited literature on effective management strategies for some of these difficult to manage corneal infections. This review highlights the current management and available evidence of atypical microbial keratitis, focusing on atypical mycobacteria keratitis, nocardia keratitis, achromobacter keratitis, and pythium keratitis. It will also describe the management of two uncommonly encountered conditions, infectious crystalline keratopathy and post-refractive infectious keratitis. This review can be used as a guide for clinicians managing patients with such challenging corneal infections.

Cannabinoid-Based Ocular Therapies and Formulations

The interest in the pharmacological applications of cannabinoids is largely increasing in a wide range of medical areas. Recently, research on its potential role in eye conditions, many of which are chronic and/or disabling and in need of new alternative treatments, has intensified. However, due to cannabinoids’ unfavorable physicochemical properties and adverse systemic effects, along with ocular biological barriers to local drug administration, drug delivery systems are needed. Hence, this review focused on the following: (i) identifying eye disease conditions potentially subject to treatment with cannabinoids and their pharmacological role, with emphasis on glaucoma, uveitis, diabetic retinopathy, keratitis and the prevention of Pseudomonas aeruginosa infections; (ii) reviewing the physicochemical properties of formulations that must be controlled and/or optimized for successful ocular administration; (iii) analyzing works evaluating cannabinoid-based formulations for ocular administration, with emphasis on results and limitations; and (iv) identifying alternative cannabinoid-based formulations that could potentially be useful for ocular administration strategies. Finally, an overview of the current advances and limitations in the field, the technological challenges to overcome and the prospective further developments, is provided.

Differential Susceptibility of Mixed Polymicrobial Biofilms Involving Ocular Coccoid Bacteria (Staphylococcus aureus and S. epidermidis) and a Filamentous Fungus (Fusarium solani) on Ex Vivo Human Corneas

Biofilms confer several advantages to the organisms associated with them, such as increased resistances to antibacterial and antifungal compounds compared to free living cells. Compared to monomicrobial biofilms involving a single microorganism, biofilms composed of microorganisms affiliated to bacterial and fungal kingdoms are predominant in nature. Despite the predominance of polymicrobial biofilms, and more so mixed polymicrobial biofilms, they are rarely studied. The objective of the current study is to evaluate the potential of ocular bacteria and a filamentous fungus to form monomicrobial and mixed polymicrobial biofilms on synthetic and natural substrates and to monitor their response to antibiotics. In this sense, we demonstrated that the ocular pathogens Staphylococcus aureus, S. epidermidis, and Fusarium solani form monomicrobial and mixed polymicrobial biofilms both on tissue culture polystyrene plates and on ex vivo human corneas from cadavers using confocal microscopy and scanning electron microscopy. Additionally, the mixed polymicrobial biofilms involving the above ocular bacteria and a filamentous fungus were less susceptible to different antibacterials and antifungals in relation to the corresponding control planktonic cells. Further, the MICs to the screened antibacterials and antifungals in polymicrobial biofilms involving a bacterium or a fungus was either increased, decreased, or unchanged compared to the corresponding individual bacterial or fungal biofilm. The results would be useful to the ophthalmologist to plan effective treatment regimens for the eye since these are common pathogens of the eye causing keratitis, endophthalmitis, conjunctivitis, etc.

Betaine- and L-Carnitine-Based Ionic Liquids as Solubilising and Stabilising Agents for the Formulation of Antimicrobial Eye Drops Containing Diacerein

The therapeutic efficacy of topically administered drugs, however powerful, is largely affected by their bioavailability and, thus, ultimately, on their aqueous solubility and stability. The aim of this study was to evaluate the use of ionic liquids (ILs) as functional excipients to solubilise, stabilise, and prolong the ocular residence time of diacerein (DIA) in eye drop formulations. DIA is a poorly soluble and unstable anthraquinone prodrug, rapidly hydrolysed to rhein (Rhe), for the treatment of osteoarthritis. DIA has recently been evaluated as an antimicrobial agent for bacterial keratitis. Two ILs based on natural zwitterionic compounds were investigated: L-carnitine C6 alkyl ester bromide (Carn6), and betaine C6 alkyl ester bromide (Bet6). The stabilising, solubilising, and mucoadhesive properties of ILs were investigated, as well as their cytotoxicity to the murine fibroblast BALB/3T3 clone A31 cell line. Two IL-DIA-based eye drop formulations were prepared, and their efficacy against both Staphylococcus aureus and Pseudomonas aeruginosa was determined. Finally, the eye drops were administered in vivo on New Zealand albino rabbits, testing their tolerability as well as their elimination and degradation kinetics. Both Bet6 and Carn6 have good potential as functional excipients, showing solubilising, stabilising, mucoadhesive, and antimicrobial properties; their in vitro cytotoxicity and in vivo ocular tolerability pave the way for their future use in ophthalmic applications.

Phosphorylcholine-Based Contact Lenses for Sustained Release of Resveratrol: Design, Antioxidant and Antimicrobial Performances, and In Vivo Behavior

Design of advanced contact lenses (CLs) demands materials that are safe and comfortable for the wearers and that preserve the normal eye microbiota, avoiding chronic inflammation and biofilm development. This work aimed to combine the natural antibiofouling phosphorylcholine and the antioxidant and prebiotic resveratrol as integral components of CLs that may have the additional performance of preventing oxidative-stress related eye diseases. Different from previous uses of 2-methacryloyloxyethyl phosphorylcholine (MPC) as coating, we explored the feasibility of adding MPC at high proportions as a comonomer of 2-hydroxyethyl methacrylate (HEMA)-based hydrogels while still allowing for the loading of the hydrophobic resveratrol. Homogeneous distribution of MPC along the hydrogel depth (confirmed by Raman spectroscopy) notably increased solvent uptake and the proportion of free water while it decreased Young's modulus. Relevantly, MPC did not hinder the uptake of resveratrol by CLs (>10 mg/g), which indeed showed network/water partition coefficients of >100. Protocols for CLs sterilization and loading of resveratrol under aseptic conditions were implemented, and the effects of tear proteins on resveratrol release rate were investigated. CLs sustained resveratrol release for more than 24 h in vitro, and sorption of albumin onto the hydrogel, although attenuated by MPC, slowed down the release. The combination of MPC and resveratrol reduced P. aeruginosa and S. aureus growth as tested in a novel hydrogel disk-agar interface biofilm growth setup. The developed CLs showed excellent anti-inflammatory properties and biocompatibility in in ovo and rabbit tests and provided higher and more prolonged levels of resveratrol in tear fluid, which favored resveratrol biodistribution in anterior and posterior eye segments compared to eye drops. Correlations between the release profiles of resveratrol in vitro and in vivo were assessed. Relevantly, the CLs preserved the antioxidant properties of resveratrol during the entire 8 h of wearing. In sum, CLs prepared with high proportion in MPC may help address safety and comfort requirements while having drug releasing capabilities.

Biofilms: Formation, Research Models, Potential Targets, and Methods for Prevention and Treatment

Due to the continuous rise in biofilm-related infections, biofilms seriously threaten human health. The formation of biofilms makes conventional antibiotics ineffective and dampens immune clearance. Therefore, it is important to understand the mechanisms of biofilm formation and develop novel strategies to treat biofilms more effectively. This review article begins with an introduction to biofilm formation in various clinical scenarios and their corresponding therapy. Established biofilm models used in research are then summarized. The potential targets which may assist in the development of new strategies for combating biofilms are further discussed. The novel technologies developed recently for the prevention and treatment of biofilms including antimicrobial surface coatings, physical removal of biofilms, development of new antimicrobial molecules, and delivery of antimicrobial agents are subsequently presented. Finally, directions for future studies are pointed out.

Transcriptomic and systems biology identifies non-antibiotic drugs for treatment of ocular bacterial infection

Increasing antibiotic resistance among ocular pathogens often results in treatment failure for blinding infections such as endophthalmitis. Hence, newer therapeutics is needed to combat multidrug-resistant infections. Here, we show a drug repurposing approach using a connectivity map based on temporal transcriptomics of Staphylococcus aureus (SA) infected mouse retina. The analysis predicted three non-antibiotic drugs, Dequalinium chloride (DC), Clofilium tosylate (CT), and Glybenclamide (Glb) which reversed the SA infection signatures. Predicted drugs exhibited anti-inflammatory properties in human retinal cells against sensitive and resistant strains of SA. Intravitreal administration of all drugs reduced intraocular inflammation in SA-infected mouse eyes while DC and CT also reduced bacterial burden. Drug treatment improved visual function coinciding with reduced Caspase-3 mediated retinal cell death. Importantly, all drugs exhibited synergy with vancomycin in improving disease outcomes. Overall, our study identified three non-antibiotic drugs and demonstrated their therapeutic and prophylactic efficacies in ameliorating intraocular bacterial infection.

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CMap analysis predicted three drugs to reverse Staphylococcus aureus endophthalmitis signature

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Drugs attenuated MRSA and MSSA induced inflammatory response in retinal cells

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Drug treatment ameliorated experimental S. aureus endophthalmitis

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Predicted drugs exhibited adjunct therapeutic potential with antibiotic

Elevated c-di-GMP Levels and Expression of the Type III Secretion System Promote Corneal Infection by Pseudomonas aeruginosa

Pseudomonas aeruginosa is generally believed to establish biofilm-associated infections under the regulation of the secondary messenger c-di-GMP. To evaluate P. aeruginosa biofilm physiology during ocular infections, comparative transcriptomic analysis was performed on wild-type P. aeruginosa PAO1, a ΔwspF mutant strain (high c-di-GMP levels), and a p_lac-yhjH-containing strain (low c-di-GMP levels) from mouse corneal infection, as well as in vitro biofilm and planktonic cultures. The c-di-GMP content in P. aeruginosa during corneal infection was monitored using a fluorescent c-di-GMP reporter strain. Biofilm-related genes were induced in in vivo PAO1 compared to in vitro planktonic bacteria. Several diguanylate cyclases and phosphodiesterases were commonly regulated in in vivo PAO1 and in vitro biofilm compared to in vitro planktonic bacteria. Several exopolysaccharide genes and motility genes were induced and downregulated, respectively, in in vivo PAO1 and the in vivo ΔwspF mutant compared to the in vivo p_lac-yhjH-containing strain. Elevation of c-di-GMP levels in P. aeruginosa began as early as 2 h postinfection. The ΔwspF mutant was less susceptible to host clearance than the p_lac-yhjH-containing strain and could suppress host immune responses. The type III secretion system (T3SS) was induced in in vivo PAO1 compared to in vitro biofilm bacteria. A ΔwspF mutant with a defective T3SS was more susceptible to host clearance than a ΔwspF mutant with a functional T3SS. Our study suggests that elevated intracellular c-di-GMP levels and T3SS activity in P. aeruginosa are necessary for establishment of infection and modulation of host immune responses in mouse cornea.

Polymicrobial biofilms of ocular bacteria and fungi on ex vivo human corneas

Microbes residing in biofilms confer several fold higher antimicrobial resistances than their planktonic counterparts. Compared to monomicrobial biofilms, polymicrobial biofilms involving multiple bacteria, multiple fungi or both are more dominant in nature. Paradoxically, polymicrobial biofilms are less studied. In this study, ocular isolates of Staphylococcus aureus, S. epidermidis and Candida albicans, the etiological agents of several ocular infections, were used to demonstrate their potential to form mono- and polymicrobial biofilms both in vitro and on human cadaveric corneas. Quantitative (crystal violet and XTT methods) and qualitative (confocal and scanning electron microscopy) methods demonstrated that they form polymicrobial biofilms. The extent of biofilm formation was dependent on whether bacteria and fungi were incubated simultaneously or added to a preformed biofilm. Additionally, the polymicrobial biofilms exhibited increased resistance to different antimicrobials compared to planktonic cells. When the MBECs of different antibacterial and antifungal agents were monitored it was observed that the MBECs in the polymicrobial biofilms was either identical or decreased compared to the monomicrobial biofilms. The results are relevant in planning treatment strategies for the eye. This study demonstrates that ocular bacteria and fungi form polymicrobial biofilms and exhibit increase in antimicrobial resistance compared to the planktonic cells.

The Current Knowledge on the Pathogenesis of Tissue and Medical Device-Related Biofilm Infections

Biofilm is the trigger for the majority of infections caused by the ability of microorganisms to adhere to tissues and medical devices. Microbial cells embedded in the biofilm matrix are highly tolerant to antimicrobials and escape the host immune system. Thus, the refractory nature of biofilm-related infections (BRIs) still represents a great challenge for physicians and is a serious health threat worldwide. Despite its importance, the microbiological diagnosis of a BRI is still difficult and not routinely assessed in clinical microbiology. Moreover, biofilm bacteria are up to 100–1000 times less susceptible to antibiotics than their planktonic counterpart. Consequently, conventional antibiograms might not be representative of the bacterial drug susceptibility in vivo. The timely recognition of a BRI is a crucial step to directing the most appropriate biofilm-targeted antimicrobial strategy.

Microbial biofilms: Recent advances and progress in environmental bioremediation

Microbial biofilms are formed by adherence of the bacteria through their secreted polymer matrices. The major constituents of the polymer matrices are extracellular DNAs, proteins, polysaccharides. Biofilms have exhibited a promising role in the area of bioremediation. These activities can be further improved by tuning the parameters like quorum sensing, characteristics of the adhesion surface, and other environmental factors. Organic pollutants have created a global concern because of their long-term toxicity on human, marine, and animal life. These contaminants are not easily degradable and continue to prevail in the environment for an extended period. Biofilms are being used for the remediation of different pollutants, among which organic pollutants have been of significance. The bioremediation of organic contaminants using biofilms is an eco-friendly, cheap, and green process. However, the development of this technology demands knowledge on the mechanism of action of the microbes to form the biofilm, types of specific bacteria or fungi responsible for the degradation of a particular organic compound, and the mechanistic role of the biofilm in the degradation of the pollutants. This review puts forth a comprehensive summary of the role of microbial biofilms in the bioremediation of different environment-threatening organic pollutants.

Comparative Evaluation of Antimicrobial, Antiamoebic, and Antiviral Efficacy of Ophthalmic Formulations

The extensive use of ophthalmic antibiotics is contributing to the appearance of resistant bacterial strains, which require prolonged and massive treatments with consequent detrimental outcomes and adverse effects. In addition to these issues, antibiotics are not effective against parasites and viruses. In this context, antiseptics could be valuable alternatives. They have nonselective mechanisms of action preventing bacterial resistance and a broad spectrum of action and are also effective against parasites and viruses. Here, we compare the in vitro antibacterial, antiameobic, and antiviral activities of six ophthalmic formulations containing antiseptics such as povidone-iodine, chlorhexidine, and thymol against Gram-positive and Gram-negative bacteria, the amoeba Acanthamoeba castellanii, and two respiratory viruses, HAdV-2 and HCoV-OC43. The results suggest that, among all the tested formulations, Dropsept, consisting of Vitamin E TPGS-based (tocopheryl polyethylene glycol succinate) in combination with the antiseptic chlorhexidine, is the one with the highest range of activities, as it works efficiently against bacteria, amoeba, and viruses. On the other hand, the solution containing PVA (polyvinyl alcohol) and thymol showed a promising inhibitory effect on Pseudomonas aeruginosa, which causes severe keratitis. Given its high efficiency, Dropsept might represent a valuable alternative to the widely used antibiotics for the treatment of ocular infections. In addition to this commercial eye drop solution, thymol-based solutions might be enrolled for their natural antimicrobial and antiamoebic effect.

Economic significance of biofilms: a multidisciplinary and cross-sectoral challenge

The increasing awareness of the significance of microbial biofilms across different sectors is continuously revealing new areas of opportunity in the development of innovative technologies in translational research, which can address their detrimental effects, as well as exploit their benefits. Due to the extent of sectors affected by microbial biofilms, capturing their real financial impact has been difficult. This perspective highlights this impact globally, based on figures identified in a recent in-depth market analysis commissioned by the UK’s National Biofilms Innovation Centre (NBIC). The outputs from this analysis and the workshops organised by NBIC on its research strategic themes have revealed the breath of opportunities for translational research in microbial biofilms. However, there are still many outstanding scientific and technological challenges which must be addressed in order to catalyse these opportunities. This perspective discusses some of these challenges.

Environmental, Microbiological, and Immunological Features of Bacterial Biofilms Associated with Implanted Medical Devices

The spread of biofilms on medical implants represents one of the principal triggers of persistent and chronic infections in clinical settings, and it has been the subject of many studies in the past few years, with most of them focused on prosthetic joint infections. We review here recent works on biofilm formation and microbial colonization on a large variety of indwelling devices, ranging from heart valves and pacemakers to urological and breast implants and from biliary stents and endoscopic tubes to contact lenses and neurosurgical implants. We focus on bacterial abundance and distribution across different devices and body sites and on the role of environmental features, such as the presence of fluid flow and properties of the implant surface, as well as on the interplay between bacterial colonization and the response of the human immune system.

Emerging nanotechnologies for targeting antimicrobial resistance

Antimicrobial resistance is a leading cause of mortality worldwide. Without newly approved antibiotics and antifungals being brought to the market, resistance is being developed to the ones currently available to clinicians. The reason is the applied evolutionary pressure to bacterial and fungal species due to the wide overuse of common antibiotics and antifungals in clinical practice and agriculture. Biofilms harbour antimicrobial-resistant subpopulations, which make their antimicrobial treatment even more challenging. Nanoparticle-based technologies have recently been shown to successfully overcome antimicrobial resistance in both planktonic and biofilms phenotypes. This results from the combination of novel nanomaterial research and classic antimicrobial therapies which promise to deliver a whole new generation of high-performance active nanocarrier systems. This review discusses the latest developments of promising nanotechnologies with applications against resistant pathogens and evaluates their potential and feasibility for use in novel antimicrobial therapies.

Clinical features of endophthalmitis clusters after cataract surgery and practical recommendations to mitigate risk: systematic review

Intraocular transmission of exogenous pathogens in cataract surgery can lead to endophthalmitis. This review evaluates the features of endophthalmitis clusters secondary to pathogen transmission in cataract surgery. Articles reporting on pathogen transmission in cataract surgery were identified via searches of Ovid MEDLINE, EMBASE, and Cochrane CENTRAL, and a total of 268 eyes from 24 studies were included. The most common source of infectious transmission was attributed to a contaminated intraocular solution (ie, irrigation solution, viscoelastic, or diluted antibiotic; n = 10). Visual acuity at presentation with infectious features was 1.89 logMAR (range: 1.35 to 2.58; ∼counting fingers) and 1.33 logMAR (range: 0.04 to 3.00; Snellen: ∼20/430) at last follow-up. Patients with diabetes had worse outcomes compared with patients without diabetes. The most frequently isolated pathogen from the infectious sources was Pseudomonas sp. (50.0%). This review highlights the various routes of pathogen transmission during cataract surgery and summarizes recommendations for the detection, prevention, and management of endophthalmitis clusters.

Plant-derived nanotherapeutic systems to counter the overgrowing threat of resistant microbes and biofilms

Since antiquity, the survival of human civilization has always been threatened by the microbial infections. An alarming surge in the resistant microbial strains against the conventional drugs is quite evident in the preceding years. Furthermore, failure of currently available regimens of antibiotics has been highlighted by the emerging threat of biofilms in the community and hospital settings. Biofilms are complex dynamic composites rich in extracellular polysaccharides and DNA, supporting plethora of symbiotic microbial life forms, that can grow on both living and non-living surfaces. These enforced structures are impervious to the drugs and lead to spread of recurrent and non-treatable infections. There is a strong realization among the scientists and healthcare providers to work out alternative strategies to combat the issue of drug resistance and biofilms. Plants are a traditional but rich source of effective antimicrobials with wider spectrum due to presence of multiple constituents in perfect synergy. Other than the biocompatibility and the safety profile, these phytochemicals have been repeatedly proven to overcome the non-responsiveness of resistant microbes and films via multiple pathways such as blocking the efflux pumps, better penetration across the cell membranes or biofilms, and anti-adhesive properties. However, the unfavorable physicochemical attributes and stability issues of these phytochemicals have hampered their commercialization. These issues of the phytochemicals can be solved by designing suitably constructed nanoscaled structures. Nanosized systems can not only improve the physicochemical features of the encapsulated payloads but can also enhance their pharmacokinetic and therapeutic profile. This review encompasses why and how various types of phytochemicals and their nanosized preparations counter the microbial resistance and the biofouling. We believe that phytochemical in tandem with nanotechnological innovations can be employed to defeat the microbial resistance and biofilms. This review will help in better understanding of the challenges associated with developing such platforms and their future prospects.

Diagnostic armamentarium of infectious keratitis: A comprehensive review

Infectious keratitis (IK) represents the leading cause of corneal blindness worldwide, particularly in developing countries. A good outcome of IK is contingent upon timely and accurate diagnosis followed by appropriate interventions. Currently, IK is primarily diagnosed on clinical grounds supplemented by microbiological investigations such as microscopic examination with stains, and culture and sensitivity testing. Although this is the most widely accepted practice adopted in most regions, such an approach is challenged by several factors, including indistinguishable clinical features shared among different causative organisms, polymicrobial infection, long diagnostic turnaround time, and variably low culture positivity rate. In this review, we aim to provide a comprehensive overview of the current diagnostic armamentarium of IK, encompassing conventional microbiological investigations, molecular diagnostics (including polymerase chain reaction and mass spectrometry), and imaging modalities (including anterior segment optical coherence tomography and in vivo confocal microscopy). We also highlight the potential roles of emerging technologies such as next-generation sequencing, artificial intelligence-assisted platforms. and tele-medicine in shaping the future diagnostic landscape of IK.

Antibiofilm and repair activity of ozonated oil in liposome

The use of medical devices, such as contact lenses, represents a substantial risk of infection, as they can act as scaffolds for formation of microbial biofilms. Recently, the increasing emergency of antibiotic resistance has prompted the development of novel and effective antimicrobial drugs for biofilm treatment, such as oxidizing agents. The purpose of this study is to investigate the effects of Ozodrop® and Ozodrop® gel, commercial names of ozonated oil in liposomes plus hypromellose, on eradication and de novo formation of biofilms on different supports, such as plastic plates and contact lens. Our results demonstrate that ozonated liposomal sunflower oil plus hypromellose have an excellent inhibitory effect on bacterial viability and on both de novo formation and eradication of biofilms produced on plates and contact lens by Pseudomonas aeruginosa and Staphylococcus aureus. Moreover, we show that Ozodrop® formulations stimulate expression of antimicrobial peptides and that Ozodrop® gel has a strong repair activity on human epithelial cells, suggesting further applications for the treatment of non‐healing infected wounds.

Challenges and solutions in polymer drug delivery for bacterial biofilm treatment: A tissue-by-tissue account

To tackle the emerging antibiotic resistance crisis, novel antimicrobial approaches are urgently needed. Bacterial communities (biofilms) are a particular concern in this context. Biofilms are responsible for most human infections and are inherently less susceptible to antibiotic treatments. Biofilms have been linked with several challenging chronic diseases, including implant-associated osteomyelitis and chronic wounds. The specific local environments present in the infected tissues further contribute to the rise in antibiotic resistance by limiting the efficacy of systemic antibiotic therapies and reducing drug concentrations at the infection site, which can lead to reoccurring infections. To overcome the shortcomings of systemic drug delivery, encapsulation within polymeric carriers has been shown to enhance antimicrobial efficacy, permeation and retention at the infection site. In this Review, we present an overview of current strategies for antimicrobial encapsulation within polymeric carriers, comparing challenges and solutions on a tissue-by-tissue basis. We compare challenges and proposed drug delivery solutions from the perspective of the local environments for biofilms found in oral, wound, gastric, urinary tract, bone, pulmonary, vaginal, ocular and middle/inner ear tissues. We will also discuss future challenges and barriers to clinical translation for these therapeutics. The following Review demonstrates there is a significant imbalance between the research focus being placed on different tissue types, with some targets (oral and wound biofims) being extensively more studied than others (vaginal and otitis media biofilms and endocarditis). Furthermore, the importance of the local tissue environment when selecting target therapies is demonstrated, with some materials being optimal choices for certain sites of bacterial infection, while having limited applicability in others.

Microbial Warfare on Three Fronts: Mixed Biofilm of Aspergillus fumigatus and Staphylococcus aureus on Primary Cultures of Human Limbo-Corneal Fibroblasts

Background

Coinfections with fungi and bacteria in ocular pathologies are increasing at an alarming rate. Two of the main etiologic agents of infections on the corneal surface, such as Aspergillus fumigatus and Staphylococcus aureus, can form a biofilm. However, mixed fungal–bacterial biofilms are rarely reported in ocular infections. The implementation of cell cultures as a study model related to biofilm microbial keratitis will allow understanding the pathogenesis in the cornea. The cornea maintains a pathogen-free ocular surface in which human limbo-corneal fibroblast cells are part of its cell regeneration process. There are no reports of biofilm formation assays on limbo-corneal fibroblasts, as well as their behavior with a polymicrobial infection.

Objective

To determine the capacity of biofilm formation during this fungal–bacterial interaction on primary limbo-corneal fibroblast monolayers.

Results

The biofilm on the limbo-corneal fibroblast culture was analyzed by assessing biomass production and determining metabolic activity. Furthermore, the mixed biofilm effect on this cell culture was observed with several microscopy techniques. The single and mixed biofilm was higher on the limbo-corneal fibroblast monolayer than on abiotic surfaces. The A. fumigatus biofilm on the human limbo-corneal fibroblast culture showed a considerable decrease compared to the S. aureus biofilm on the limbo-corneal fibroblast monolayer. Moreover, the mixed biofilm had a lower density than that of the single biofilm. Antibiosis between A. fumigatus and S. aureus persisted during the challenge to limbo-corneal fibroblasts, but it seems that the fungus was more effectively inhibited.

Conclusion

This is the first report of mixed fungal–bacterial biofilm production and morphological characterization on the limbo-corneal fibroblast monolayer. Three antibiosis behaviors were observed between fungi, bacteria, and limbo-corneal fibroblasts. The mycophagy effect over A. fumigatus by S. aureus was exacerbated on the limbo-corneal fibroblast monolayer. During fungal–bacterial interactions, it appears that limbo-corneal fibroblasts showed some phagocytic activity, demonstrating tripartite relationships during coinfection.

Both Pseudomonas aeruginosa and Candida albicans Accumulate Greater Biomass in Dual-Species Biofilms under Flow

Microbe-microbe interactions can strongly influence growth and biofilm formation kinetics. For Pseudomonas aeruginosa and Candida albicans, which are found together in diverse clinical sites, including urinary and intravenous catheters and the lungs of individuals with cystic fibrosis (CF), we compared the kinetics of biofilm formation by each species in dual-species and single-species biofilms. We engineered fluorescent protein constructs for P. aeruginosa (producing mKO-κ) and C. albicans (producing mKate2) that did not alter growth and enabled single-cell resolution imaging by live-sample microscopy. Using these strains in an optically clear derivative of synthetic CF sputum medium, we found that both P. aeruginosa and C. albicans displayed increased biovolume accumulation—by three- and sixfold, respectively—in dual-species biofilms relative to single-species biofilms. This result was specific to the biofilm environment, as enhanced growth was not observed in planktonic cocultures. Stimulation of C. albicans biofilm formation occurred regardless of whether P. aeruginosa was added at the time of fungal inoculation or 24 h after the initiation of biofilm development. P. aeruginosa biofilm increases in cocultures did not require the Pel extracellular polysaccharide, phenazines, and siderophores known to influence C. albicans. P. aeruginosa mutants lacking Anr, LasR, and BapA were not significantly stimulated by C. albicans, but they still promoted a significant enhancement of biofilm development of the fungus, suggesting a fungal response to the presence of bacteria. Last, we showed that a set of P. aeruginosa clinical isolates also prompted an increase of biovolume by C. albicans in coculture.

IMPORTANCE There is an abundance of work on both P. aeruginosa and C. albicans in isolation, and quite some work as well on the way these two microbes interact. These studies do not, however, consider biofilm environments under flow, and our results here show that the expected outcome of interaction between these two pathogens can actually be reversed under flow, from pure antagonism to an increase in biomass on the part of both. Our work also highlights the importance of cellular-scale spatial structure in biofilms for understanding multispecies population dynamics.

Ocular Surface Microbiota in Contact Lens Users and Contact-Lens-Associated Bacterial Keratitis

Our objectives were to investigate whether the conjunctival microbiota is altered by contact lens wear and/or bacterial keratitis and to explore the hypothesis that commensals of conjunctival microbiota contribute to bacterial keratitis. Swab samples from both eyes were collected separately from the inferior fornix of the conjunctiva of non-contact-lens users (n_participants = 28) and contact lens users (n_participants = 26) and from patients with contact-lens-associated bacterial keratitis (n_participants = 9). DNA from conjunctival swab samples was analyzed with 16S rRNA gene amplicon sequencing. Pathogens from the corneal infiltrates were identified by cultivation. In total, we identified 19 phyla and 283 genera; the four most abundant genera were Pseudomonas, Enhydrobacter, Staphylococcus, and Cutibacterium. Several pathogens related to bacterial keratitis were identified in the conjunctival microbiota of the whole study population, and the same bacteria were identified by both methods in the conjunctiva and cornea for four patients with contact-lens-associated bacterial keratitis. The overall conjunctival microbiota profile was not altered by contact lens wear or bacterial keratitis; thus, it does not appear to contribute to the development of bacterial keratitis in contact lens users. However, in some individuals, conjunctival microbiota may harbor opportunistic pathogens causing contact-lens-associated bacterial keratitis.

Biofilm-Forming Potential of Ocular Fluid Staphylococcus aureus and Staphylococcus epidermidis on Ex Vivo Human Corneas from Attachment to Dispersal Phase

The biofilm-forming potential of Staphylococcus aureus and Staphylococcus epidermidis, isolated from patients with Endophthalmitis, was monitored using glass cover slips and cadaveric corneas as substrata. Both the ocular fluid isolates exhibited biofilm-forming potential by the Congo red agar, Crystal violet and 2,3-bis (2-methoxy-4-nitro-5-sulfophenyl)-5-(phenylamino) carbonyl-2H-tetra-zolium hydroxide (XTT) methods. Confocal microscopy demonstrated that the thickness of the biofilm increased from 4–120 h of biofilm formation. Scanning electron microscopic studies indicated that the biofilms grown on cover slips and ex vivo corneas of both the isolates go through an adhesion phase at 4 h followed by multilayer clumping of cells with intercellular connections and copious amounts of extracellular polymeric substance. Clumps subsequently formed columns and eventually single cells were visible indicative of dispersal phase. Biofilm formation was more rapid when the cornea was used as a substratum. In the biofilms grown on corneas, clumping of cells, formation of 3D structures and final appearance of single cells indicative of dispersal phase occurred by 48 h compared to 96–120 h when biofilms were grown on cover slips. In the biofilm phase, both were several-fold more resistant to antibiotics compared to planktonic cells. This is the first study on biofilm forming potential of ocular fluid S. aureus and S. epidermidis on cadaveric cornea, from attachment to dispersal phase of biofilm formation.

The role of nitric oxide in ocular surface physiology and pathophysiology

Nitric oxide (NO) has a wide array of biological functions including the regulation of vascular tone, neurotransmission, immunomodulation, stimulation of proinflammatory cytokine expression and antimicrobial action. These functions may depend on the type of isoform that is responsible for the synthesis of NO. NO is found in various ocular tissues playing a pivotal role in physiological mechanisms, namely regulating vascular tone in the uvea, retinal blood circulation, aqueous humor dynamics, neurotransmission and phototransduction in retinal layers. Unregulated production of NO in ocular tissues may result in production of toxic superoxide free radicals that participate in ocular diseases such as endotoxin-induced uveitis, ischemic proliferative retinopathy and neurotoxicity of optic nerve head in glaucoma. However, the role of NO on the ocular surface in mediating physiology and pathophysiological processes is not fully understood. Moreover, methods used to measure levels of NO in the biological samples of the ocular surface are not well established due to its rapid oxidation. The purpose of this review is to highlight the role of NO in the physiology and pathophysiology of ocular surface and propose suitable techniques to measure NO levels in ocular surface tissues and tears. This will improve the understanding of NO's role in ocular surface biology and the development of new NO-based therapies to treat various ocular surface diseases. Further, this review summarizes the biochemistry underpinning NO's antimicrobial action.

Resveratrol-Loaded Hydrogel Contact Lenses with Antioxidant and Antibiofilm Performance

Contact lenses (CLs) are prone to biofilm formation, which may cause severe ocular infections. Since the use of antibiotics is associated with resistance concerns, here, two alternative strategies were evaluated to endow CLs with antibiofilm features: copolymerization with the antifouling monomer 2-methacryloyloxyethyl phosphorylcholine (MPC) and loading of the antioxidant resveratrol with known antibacterial activity. MPC has, so far, been used to increase water retention on the CL surface (Proclear^® 1 day CLs). Both poly(hydroxyethyl methacrylate) (HEMA) and silicone hydrogels were prepared with MPC covering a wide range of concentrations (from 0 to 101 mM). All hydrogels showed physical properties adequate for CLs and successfully passed the hen’s egg-chorioallantoic membrane (HET-CAM) test. Silicone hydrogels had stronger affinity for resveratrol, with higher loading and a slower release rate. Ex vivo cornea and sclera permeability tests revealed that resveratrol released from the hydrogels readily accumulated in both tissues but did not cross through. The antibiofilm tests against Pseudomonas aeruginosa and Staphylococcus aureus evidenced that, in general, resveratrol decreased biofilm formation, which correlated with its concentration-dependent antibacterial capability. Preferential adsorption of lysozyme, compared to albumin, might also contribute to the antimicrobial activity. In addition, importantly, the loading of resveratrol in the hydrogels preserved the antioxidant activity, even against photodegradation. Overall, the designed hydrogels can host therapeutically relevant amounts of resveratrol to be sustainedly released on the eye, providing antibiofilm and antioxidant performance.

The ocular microbiome and microbiota and their effects on ocular surface pathophysiology and disorders

The ocular surface flora perform an important role in the defense mechanisms of the ocular surface system. Its regulation of the immunological activity and the barrier effect against pathogen invasion are remarkable. Composition of the flora differs according to the methods of investigation, because the microbiome, composed of the genetic material of bacteria, fungi, viruses, protozoa, and eukaryotes on the ocular surface, differs from the microbiota, which are the community of microorganisms that colonize the ocular surface. The observed composition of the ocular surface flora depends on harvesting and examining methods, whether with traditional culture or with more refined genetic analysis based on rRNA and DNA sequencing. Environment, diet, sex, and age influence the microbial flora composition, thus complicating the analysis of the baseline status. Moreover, potentially pathogenic organisms can affect its composition, as do various disorders, including chronic inflammation, and therapies applied to the ocular surface. A better understanding of the composition and function of microbial communities at the ocular surface could bring new insights and clarify the epidemiology and pathology of ocular surface dynamics in health and disease. The purpose of this review is to provide an up-to-date overview of knowledge about this topic.

The Role of Biofilms in Pathology of the Ocular Surface

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Corneal Infection Models: Tools to Investigate the Role of Biofilms in Bacterial Keratitis

Bacterial keratitis is a corneal infection which may cause visual impairment or even loss of the infected eye. It remains a major cause of blindness in the developing world. Staphylococcus aureus and Pseudomonas aeruginosa are common causative agents and these bacterial species are known to colonise the corneal surface as biofilm populations. Biofilms are complex bacterial communities encased in an extracellular polymeric matrix and are notoriously difficult to eradicate once established. Biofilm bacteria exhibit different phenotypic characteristics from their planktonic counterparts, including an increased resistance to antibiotics and the host immune response. Therefore, understanding the role of biofilms will be essential in the development of new ophthalmic antimicrobials. A brief overview of biofilm-specific resistance mechanisms is provided, but this is a highly multifactorial and rapidly expanding field that warrants further research. Progression in this field is dependent on the development of suitable biofilm models that acknowledge the complexity of the ocular environment. Abiotic models of biofilm formation (where biofilms are studied on non-living surfaces) currently dominate the literature, but co-culture infection models are beginning to emerge. In vitro, ex vivo and in vivo corneal infection models have now been reported which use a variety of different experimental techniques and animal models. In this review, we will discuss existing corneal infection models and their application in the study of biofilms and host-pathogen interactions at the corneal surface.

Recent Developments in Biomimetic Antifouling Materials: A Review

The term 'biomimetic' might be applied to any material or process that in some way reproduces, mimics, or is otherwise inspired by nature. Also variously termed bionic, bioinspired, biological design, or even green design, the idea of adapting or taking inspiration from a natural solution to solve a modern engineering problem has been of scientific interest since it was first proposed in the 1960s. Since then, the concept that natural materials and nature can provide inspiration for incredible breakthroughs and developments in terms of new technologies and entirely new approaches to solving technological problems has become widely accepted. This is very much evident in the fields of materials science, surface science, and coatings. In this review, we survey recent developments (primarily those within the last decade) in biomimetic approaches to antifouling, self-cleaning, or anti-biofilm technologies. We find that this field continues to mature, and emerging novel, biomimetic technologies are present at multiple stages in the development pipeline, with some becoming commercially available. However, we also note that the rate of commercialization of these technologies appears slow compared to the significant research output within the field.

Engineered lactobacilli display anti-biofilm and growth suppressing activities against Pseudomonas aeruginosa

Biofilms are an emerging target for new therapeutics in the effort to address the continued increase in resistance and tolerance to traditional antimicrobials. In particular, the distinct nature of the biofilm growth state often means that traditional antimcirobials, developed to combat planktonic cells, are ineffective. Biofilm treatments are designed to both reduce pathogen load at an infection site and decrease the development of resistance by rendering the embedded organisms more susceptible to treatment at lower antimicrobial concentrations. In this work, we developed a new antimicrobial treatment modality using engineered lactic acid bacteria (LAB). We first characterized the natural capacity of two lactobacilli, L. plantarum and L. rhamnosus, to inhibit P. aeruginosa growth, biofilm formation, and biofilm viability, which we found to be dependent upon the low pH generated during culture of the LAB. We further engineered these LAB to secrete enzymes known to degrade P. aeruginosa biofilms and show that our best performing engineered LAB, secreting a pathogen-derived enzyme (PelAh), degrades up to 85% of P. aeruginosa biofilm.

From Treatise to Test: Evaluating Traditional Remedies for Anti-Biofilm Potential

Traditional plant-based remedies hold vast potential as novel antimicrobial agents, particularly for recalcitrant infection states such as biofilms. To explore their potential, it is important to bring these remedies out of historical treatises, and into present-day scientific evaluation. Using an example of Indian traditional medicine (Ayurveda), we present a perspective toward evaluating historical remedies for anti-biofilm potential. Across compendia, we identified three plant-based remedies (of Kalanchoe pinnata, Cynodon dactylon, and Ocimum tenuiflorum) recommended for wounds. The remedies were reconstituted in accordance with historical practices, and tested for their effects on biofilm formation and eradication assays of wound pathogens, Pseudomonas aeruginosa and Staphylococcus aureus. Based on our approach and the results obtained, we provide insights into the considerations and challenges related to identifying potential remedies in historical texts, and testing them in the laboratory with standard biofilm assays. We believe this will be relevant for future studies exploring anti-biofilm approaches at the interface of historical medicine and present-day scientific practices.

A nanostructured anti-biofilm surface widens the efficacy against spindle-shaped and chain-forming rod-like bacteria

Current control of pathogenic bacteria at all biomaterial interfaces is poorly attuned to a broad range of disease-causing pathogens. Leading antimicrobial surface functionalization strategies with antimicrobial peptides (AMPs), defensins, have not shown their promised efficacy. One of the main problems is the lack of stability and swift clearance from the surface. Surface nanotopography bearing sharp protrusions is a non-chemical solution that is intrinsically stable and long-lasting. Previously, the geometrically ordered arrays of nanotipped spines repelled or rapidly ruptured bacteria that come into contact. The killing properties so far work on cocci and rod-like bacteria, but there is no validation of the efficacy of protrusional surfaces on pathogenic bacteria with different sizes and morphologies, thus broadening the utility of such surfaces to cover increasingly more disease entities. Here, we report a synthetic analogue of nanotipped spines with a pyramidal shape that show great effectiveness on species of bacteria with strongly contrasting shapes and sizes. To highlight this phenomenon in the field of dental applications where selective bacterial control is vital to the clinical success of biomaterial functions, we modified the poly(methyl)-methacrylate (PMMA) texture and tested it against Streptococcus mutans, Enterococcus faecalis, Porphyromonas gingivalis, and Fusobacterium nucleatum. These nanopyramids performed effectively at levels well above those of normal and roughened PMMA biomaterials for dentistry and a model material for general use in medicine and disease transmission in hospital environments.

Levofloxacin-loaded naturally occurring monoterpene-based nanoemulgel: a feasible efficient system to circumvent MRSA ocular infections

Staphylococcus aureus is a leading cause of ocular keratitis worldwide, and the upsurge of Methicillin-resistant Staphylococcus Aureus (MRSA) strains necessitated the development of new antimicrobial agents. D-limonene is the major constituent of oil extracted from citrus peel, which has been utilized for its gastroprotective, antifungal, antitumor, and antibacterial effects. The present study aimed to develop an effective in-situ ocular limonene-based nanoemulgel to enhance the efficacy of fluoroquinolones against MRSA associated ocular biofilm infection. The nanoemulsion composed of limonene, Tween^®80, propylene glycol at a ratio of 5:4:1 loaded with levofloxacin. The formulated levofloxacin-loaded limonene-based nanoemulsion physiochemical properties namely; droplet size, polydispersity index, zeta potential, and in-vitro drug release were studied and stability over three months was assessed. Furthermore, in-vitro antimicrobial susceptibility was investigated on biofilm-forming MRSA strain through kinetics of killing and biofilm assay. The in-situ nanoemulgel ocular irritation was studied by HET-CAM test. The results demonstrated that levofloxacin-loaded limonene-based nanoemulsion had a particle size of 119 ± 0.321 nm with improved eradicating efficacy of MRSA biofilm, where the MIC of the loaded nanoemulgel was 3.12 mg/ml significantly less than that of drug alone (6.25 mg/ml). HET-CAM test showed no signs of hemorrhage, coagulation, or lysis for the loaded nanoemulgel same as sodium chloride solution (negative control) where its irritation score was zero compared to 9.87 for the positive irritant group (1%w/v sodium lauryl sulfate). In conclusion, the current investigation provided a strong foundation for further studies of limonene nanoemulgel as a potential complementary therapeutic agent against resistant bacterial strains.

Biomimetic Functional Surfaces towards Bactericidal Soft Contact Lenses

The surface with high-aspect-ratio nanostructure is observed to possess the bactericidal properties, where the physical interaction between high-aspect-ratio nanostructure could exert sufficient pressure on the cell membrane eventually lead to cell lysis. Recent studies in the interaction mechanism and reverse engineering have transferred the bactericidal capability to artificial surface, but the biomimetic surfaces mimicking the topographical patterns on natural resources possess different geometrical parameters and surface properties. The review attempts to highlight the recent progress in bactericidal nanostructured surfaces to analyze the prominent influence factors and cell rupture mechanism. A holistic approach was utilized, integrating interaction mechanisms, material characterization, and fabrication techniques to establish inclusive insights into the topographical effect and mechano-bactericidal applications. The experimental work presented in the hydrogel material field provides support for the feasibility of potentially broadening applications in soft contact lenses.