Corneal Biofilms: From Planktonic to Microcolony Formation in an Experimental Keratitis Infection with Pseudomonas Aeruginosa

In vitro and ex vivo models of microbial keratitis: Present and future

Microbial keratitis (MK) is an infection of the cornea, caused by bacteria, fungi, parasites, or viruses. MK leads to significant morbidity, being the fifth leading cause of blindness worldwide. There is an urgent requirement to better understand pathogenesis in order to develop novel diagnostic and therapeutic approaches to improve patient outcomes. Many in vitro, ex vivo and in vivo MK models have been developed and implemented to meet this aim. Here, we present current in vitro and ex vivo MK model systems, examining their varied design, outputs, reporting standards, and strengths and limitations. Major limitations include their relative simplicity and the perceived inability to study the immune response in these MK models, an aspect widely accepted to play a significant role in MK pathogenesis. Consequently, there remains a dependence on in vivo models to study this aspect of MK. However, looking to the future, we draw from the broader field of corneal disease modelling, which utilises, for example, three-dimensional co-culture models and dynamic environments observed in bioreactors and organ-on-a-chip scenarios. These remain unexplored in MK research, but incorporation of these approaches will offer further advances in the field of MK corneal modelling, in particular with the focus of incorporation of immune components which we anticipate will better recapitulate pathogenesis and yield novel findings, therefore contributing to the enhancement of MK outcomes.

Investigation of anti-aging and anti-infection properties of Jingfang Granules using the Caenorhabditis elegans model

Jingfang Granule (JFG), a traditional Chinese medicine, is frequently employed in clinical settings for the treatment of infectious diseases. Nevertheless, the anti-aging and anti-infection effects of JFG remain uncertain. In the present study, these effects were evaluated using the Caenorhabditis elegans (C. elegans) N2 as a model organism. The results demonstrated that JFG significantly increased the median lifespan of C. elegans by 31.2% at a dosage of 10 mg/mL, without any discernible adverse effects, such as alterations in the pharyngeal pumping rate or nematode motility. Moreover, JFG notably increased oviposition by 11.3%. Subsequent investigations revealed that JFG enhanced oxidative stress resistance in C. elegans by reducing reactive oxygen species levels and significantly improved survival rates in nematodes infected with Pseudomonas aeruginosa ATCC 9027. These findings suggest that JFG delays reproductive senescence in C. elegans and protects them from oxidative stress, thereby extending their lifespan. Additionally, JFG improves the survival of P. aeruginosa-infected nematodes. Consequently, JFG has potential as a candidate for the development of anti-aging and anti-infection functional medicines.

Chitosan oligosaccharide/pluronic F127 micelles exhibiting anti-biofilm effect to treat bacterial keratitis

Mono or dual chitosan oligosaccharide lactate (COL)-conjugated pluronic F127 polymers, FCOL1 and FCOL2 were prepared, self-assembled to form micelles, and loaded with gatifloxacin. The Gati@FCOL1/Gati@FCOL2 micelles preparation process was optimized by QbD analysis. Micelles were characterized thoroughly for size, CMC, drug compatibility, and viscosity by GPC, DLS, SEM, IR, DSC, and XRD. The micelles exhibited good cellular uptake in both monolayers and spheroids of HCEC. The antibacterial and anti-biofilm activities of the micelles were evaluated on P. aeruginosa and S. aureus. The anti-quorum sensing activity was explored in P. aeruginosa by analyzing micelles' ability to produce virulence factors, including AHLs, pyocyanin, and the motility behavior of the organism. Gati@FCOL2 Ms was mucoadhesive, cornea-penetrant, antibacterial, and inhibited the biofilm formation by P. aeruginosa and S. aureus significantly more than Gati@FCOL1. A significant reduction in bacterial load in mice cornea was observed after Gati@FCOL2 Ms-treatment to the P. aeruginosa-induced bacterial keratitis-infected mice.

Antimicrobial resistance in ocular infection: A review

Antimicrobial resistance (AMR) is a global public health threat with significant impact on treatment outcomes. The World Health Organization's Global Action Plan on AMR recommended strengthening the evidence base through surveillance programs and research. Comprehensive, timely data on AMR for organisms isolated from ocular infections are needed to guide treatment decisions and inform researchers and microbiologists of emerging trends. This article aims to provide an update on the development of AMR in ocular organisms, AMR in bacterial ocular infections and on AMR stewardship programs globally. The most common ocular pathogens are Pseudomonas aeruginosa, Staphylococcus spp., Streptococcus pneumoniae, and Haemophilus influenzae in ocular infections. A variety of studies and a few surveillance programs worldwide have reported on AMR in these infections over time. Fluoroquinolone resistance has increased particularly in Asia and North America. For conjunctivitis, the ARMOR cumulative study in the USA reported a slight decrease in resistance to ciprofloxacin. For keratitis, resistance to methicillin has remained stable for S. aureus and CoNS, while resistance to ciprofloxacin has decreased for MRSA globally. Methicillin-resistance and multidrug resistance are also emerging, requiring ongoing monitoring. Antimicrobial stewardship (AMS) programmes have a critical role in reducing the threat of AMR and improving treatment outcomes. To be successful AMS must be informed by up-to-date AMR surveillance data. As a profession it is timely for ophthalmology to act to prevent AMR leading to greater visual loss through supporting surveillance programmes and establishing AMS.

Tools of the Trade: Image Analysis Programs for Confocal Laser-Scanning Microscopy Studies of Biofilms and Considerations for Their Use by Experimental Researchers

Confocal laser-scanning microscopy (CLSM) is the bedrock of the microscopic visualization of biofilms. Previous applications of CLSM in biofilm studies have largely focused on observations of bacterial or fungal elements of biofilms, often seen as aggregates or mats of cells. However, the field of biofilm research is moving beyond qualitative observations alone, toward the quantitative analysis of the structural and functional features of biofilms, across clinical, environmental, and laboratory conditions. In recent times, several image analysis programs have been developed to extract and quantify biofilm properties from confocal micrographs. These tools not only vary in their scope and relevance to the specific biofilm features under study but also with respect to the user interface, compatibility with operating systems, and raw image requirements. Understanding these considerations is important when selecting tools for quantitative biofilm analysis, including at the initial experimental stages of image acquisition. In this review, we provide an overview of image analysis programs for confocal micrographs of biofilms, with a focus on tool selection and image acquisition parameters that are relevant for experimental researchers to ensure reliability and compatibility with downstream image processing.

Establishing an Experimental Pseudomonas aeruginosa Keratitis Model in Mice - Challenges and Solutions

BACKGROUND

With the ongoing increase in antimicrobial resistances seen in bacterial isolates causing a keratitis in humans, animal models have become an important tool to study new antimicrobial therapies. Nevertheless, the establishment of experimental keratitis is difficult. Here, we discuss the impact of different arrangements, including animal age, bacterial strain and dose as well as epithelium removal on the outcome of experimental keratitis. We therefore present the methods and results of our establishing experiments.

METHODS

Bacterial load determination and flow cytometry were performed using eye homogenate gained from a 72hours lasting murine Pseudomonas aeruginosa keratitis model. Additionally, the intensity of the infection was scored from 0 to 5, the mice weighed, and blood immune cells counted.

RESULTS

We found that older C57BL/6N mice (8-11 months) are more susceptible to develop a keratitis than younger mice (5-6 weeks). Epithelium removal has no major impact on infectivity and disease progression in aged mice. P. aeruginosa exoU⁺ strains, such as PA54, should preferentially be used and highly concentrated (∼ 5×10⁷ CFU). Establishing an infection with the exoU^- PAO1 derivative DSM 19880 was not possible.

CONCLUSIONS

We present a replicable method to achieve a successful experimental P. aeruginosa keratitis in C57BL/6N mice that is sustained or aggravated over the observation period of 3 days in 80% of all animals tested. Our work is of particular interest to all researchers planning the establishment of such experimental models. We show some key aspects that can simplify and quicken the procedure, ultimately saving costs and animal life.

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.

Infectious Crystalline Keratopathy after Penetrating Keratoplasty with Light and Electron Microscopic Examination

PURPOSE

To highlight the typical histological and ultrastructural features of severe infectious crystalline keratopathy (ICK) in a corneal graft, which required excimer laser-assisted repeat penetrating keratoplasty (PKP) and to present the challenging treatment conditions associated with ICK.

METHODS

An 85-year-old female patient underwent PKP for secondary graft failure after Descemet membrane endothelial keratoplasty (DMEK) for Fuchs' endothelial corneal dystrophy in the left eye. One year later, white branched opacities were observed in the superficial corneal stroma of the graft without surrounding inflammation in the left eye. The patient underwent excimer laser-assisted repeat PKP (8.0/8.1 mm) in the left eye after prolonged refractory topical anti-infectious treatment for 1 month. The corneal explant was further examined by light and transmission electron microscopy (TEM).

RESULTS

The light microscopic examination of the corneal explant demonstrated aggregates of coccoid bacteria in the superficial and mid-stromal region that were positive for periodic acid-Schiff (PAS) and Gram stain. The bacterial aggregates extended into the interlamellar spaces, showed a spindle-shaped appearance, and were not surrounded by an inflammatory cellular reaction. TEM demonstrated lamellae separation within the anterior corneal stroma with spindle-shaped aggregates of bacteria, which were embedded in an extracellular amorphous matrix with incipient calcification, being consistent with a biofilm. No inflammatory cellular reaction was evident by TEM. At discharge from hospital, the corrected visual acuity was 20/80 in the left eye.

CONCLUSION

ICK is often challenging due to the difficult diagnosis and treatment conditions. The refractory courses are mainly attributed to a biofilm formation, which inhibits effective topical anti-infectious treatment. In such cases, (repeat) PKP may be necessary to completely remove the pathology, prevent recurrences, and improve vision.

Antimicrobial Efficacy of Extracts of Saudi Arabian Desert Terfezia claveryi Truffles

Background

Terfezia claveryi truffles are known for their nutritional value and have been considered among traditional treatments for ophthalmic infections and ailments.

Objectives

We sought to investigate the in vitro antimicrobial efficacy of several T. claveryi extracts from Saudi Arabia. Certain pathogenic fungi and gram-negative and gram-positive bacteria were included.

Methods

Dry extracts were prepared using methanol, ethyl acetate, and distilled water, while the latter was used for preparing fresh extracts. The extracts were microbiologically evaluated through the disc-diffusion agar method; the zones of inhibition of microbial growth were measured post-incubation. The minimum bactericidal concentration (MBC) and minimum inhibitory concentration (MIC) were determined in Müller-Hinton Broth through the microdilution susceptibility method. anti-biofilm activity was assessed for potent extracts.

Results

Dry extracts showed potent activity (>16-mm inhibition zones) against gram-positive (Bacillus subtilis IFO3007 and Staphylococcus aureus IFO3060) and gram-negative (Pseudomonas aeruginosa IFO3448 and Escherichia coli IFO3301) bacteria. The activity against fungi was moderate (12–16-mm inhibition zones) for both Aspergillus oryzae IFO4177 and Candida albicans IFO0583; there was no activity against Aspergillus niger IFO4414 growth. Methanolic extract had the lowest MIC and MBC, exhibiting remarkable activity against B. subtilis growth. Fresh extract showed moderate activity against bacterial growth and inactivity against fungal growth. Methanolic extract showed potent anti-biofilm activity (IC₅₀, 2.0 ± 0.18 mg/mL) against S. aureus.

Conclusions

T. claveryi extracts showed antibacterial effects potentially suitable for clinical application, which warrants further in-depth analysis of their individual isolated compounds.

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 plac-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 plac-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 plac-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.

Pharmacological perturbation of thiamine metabolism sensitizes Pseudomonas aeruginosa to multiple antibacterial agents

New therapeutic concepts are critically needed for carbapenem-resistant Pseudomonas aeruginosa, an opportunistic pathogen particularly recalcitrant to antibiotics. The screening of around 230,000 small molecules yielded a very low hit rate of 0.002% after triaging for known antibiotics. The only novel hit that stood out was the antimetabolite oxythiamine. Oxythiamine is a known transketolase inhibitor in eukaryotic cells, but its antibacterial potency has not been reported. Metabolic and transcriptomic analyses indicated that oxythiamine is intracellularly converted to oxythiamine pyrophosphate and subsequently inhibits several vitamin-B1-dependent enzymes, sensitizing the bacteria to several antibiotic and non-antibiotic drugs such as tetracyclines, 5-fluorouracil, and auranofin. The positive interaction between 5-fluorouracil and oxythiamine was confirmed in a murine ocular infection model, indicating relevance during infection. Together, this study revealed a system-level significance of thiamine metabolism perturbation that sensitizes P. aeruginosa to multiple small molecules, a property that could inform on the development of a rational drug combination.

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.

Role of Extracellular Trap Release During Bacterial and Viral Infection

Neutrophils are innate immune cells that play an essential role during the clearance of pathogens that can release chromatin structures coated by several cytoplasmatic and granular antibacterial proteins, called neutrophil extracellular traps (NETs). These supra-molecular structures are produced to kill or immobilize several types of microorganisms, including bacteria and viruses. The contribution of the NET release process (or NETosis) to acute inflammation or the prevention of pathogen spreading depends on the specific microorganism involved in triggering this response. Furthermore, studies highlight the role of innate cells different from neutrophils in triggering the release of extracellular traps during bacterial infection. This review summarizes the contribution of NETs during bacterial and viral infections, explaining the molecular mechanisms involved in their formation and the relationship with different components of such pathogens.

Paradox of complex diversity: Challenges in the diagnosis and management of bacterial keratitis

Bacterial keratitis continues to be one of the leading causes of corneal blindness in the developed as well as the developing world, despite swift progress since the dawn of the "anti-biotic era". Although, we are expeditiously developing our understanding about the different causative organisms and associated pathology leading to keratitis, extensive gaps in knowledge continue to dampen the efforts for early and accurate diagnosis, and management in these patients, resulting in poor clinical outcomes. The ability of the causative bacteria to subdue the therapeutic challenge stems from their large genome encoding complex regulatory networks, variety of unique virulence factors, and rapid secretion of tissue damaging proteases and toxins. In this review article, we have provided an overview of the established classical diagnostic techniques and therapeutics for keratitis caused by various bacteria. We have extensively reported our recent in-roads through novel tools for accurate diagnosis of mono- and poly-bacterial corneal infections. Furthermore, we outlined the recent progress by our group and others in understanding the sub-cellular genomic changes that lead to antibiotic resistance in these organisms. Finally, we discussed in detail, the novel therapies and drug delivery systems in development for the efficacious management of bacterial keratitis.

Biofilm Formation by Pseudomonas aeruginosa in a Novel Septic Arthritis Model

Background

Bacterial biofilms generally contribute to chronic infections and complicate effective treatment outcomes. To date, there have been no reports describing biofilm formation in animal models of septic arthritis caused by Pseudomonas aeruginosa (P. aeruginosa). P. aeruginosa is an opportunistic pathogenic bacterium which can lead to septic arthritis. The purpose of this study was to establish a rabbit model of septic arthritis caused by P. aeruginosa to determine whether it leads to biofilm formation in the knee joint cavity. In addition, we explored the role of cyclic di-GMP (c-di-GMP) concentrations in biofilm formation in rabbit models.

Methods

Twenty rabbits were randomly assigned to five groups: PAO1 (n = 4), PAO1ΔwspF (n = 4), PAO1/p_lac-yhjH (n = 4) infection group, Luria–Bertani (LB) broth (n = 4), and magnesium tetrasilicate (talc) (n = 4) control groups. Inoculation in the rabbit knee of P. aeruginosa or with the same volume of sterile LB or talc in suspension (control group) was used to induce septic arthritis in the animal model. In the infection groups, septic arthritis was caused by PAO1, PAO1ΔwspF, and PAO1/p_lac-yhjH strains, respectively. Rabbits were euthanized after 7 days, and pathological examination of synovial membrane was performed. The biofilms on the surface of the synovial membrane were observed by scanning electron microscopy, while the biofilms’ fiber deposition was discriminated using peptide nucleic acid-fluorescence in situ hybridization (PNA-FISH).

Results

A rabbit model for knee septic arthritis induced by P. aeruginosa was successfully established. Scanning electron microscopy revealed that PAO1 strains were surrounded in a self-produced extracellular matrix on the surface of synovial membrane and showed biofilm structures. The biofilms in the fibrous deposition were also observed by PNA-FISH. The PNA-FISH assay revealed that the red fluorescence size in the PAO1ΔwspF group was greater than in PAO1 and PAO1/p_lac-yhjH groups.

Conclusions

This is the first study to provide evidence that P. aeruginosa forms biofilms in a rabbit model for septic knee arthritis. The rabbit model can be used to investigate new approaches to treatment of biofilms in septic arthritis. Furthermore, c-di-GMP is a key signaling molecule which impacts on biofilm formation in rabbit models of knee septic arthritis.

Imaging Infection Across Scales of Size: From Whole Animals to Single Molecules

Infectious diseases are a leading cause of global morbidity and mortality, and the threat of infectious diseases to human health is steadily increasing as new diseases emerge, existing diseases reemerge, and antimicrobial resistance expands. The application of imaging technology to the study of infection biology has the potential to uncover new factors that are critical to the outcome of host-pathogen interactions and to lead to innovations in diagnosis and treatment of infectious diseases. This article reviews current and future opportunities for the application of imaging to the study of infectious diseases, with a particular focus on the power of imaging objects across a broad range of sizes to expand the utility of these approaches. Expected final online publication date for the Annual Review of Microbiology, Volume 75 is October 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Foundational concepts in the biology of bacterial keratitis

Bacterial infections of the cornea, or bacterial keratitis (BK), are notorious for causing rapidly fulminant disease and permanent vision loss, even among treated patients. In the last sixty years, dramatic upward trajectories in the frequency of BK have been observed internationally, driven in large part by the commercialization of hydrogel contact lenses in the late 1960s. Despite this worsening burden of disease, current evidence-based therapies for BK - including broad-spectrum topical antibiotics and, if indicated, topical corticosteroids - fail to salvage vision in a substantial proportion of affected patients. Amid growing concerns of rapidly diminishing antibiotic utility, there has been renewed interest in urgently needed novel treatments that may improve clinical outcomes on an individual and public health level. Bridging the translational gap in the care of BK requires the identification of new therapeutic targets and rational treatment design, but neither of these aims can be achieved without understanding the complex biological processes that determine how bacterial corneal infections arise, progress, and resolve. In this chapter, we synthesize the current wealth of human and animal experimental data that now inform our understanding of basic BK pathophysiology, in context with modern concepts in ocular immunology and microbiology. By identifying the key molecular determinants of clinical disease, we explore how novel treatments can be developed and translated into routine patient care.

Quantitative Proteomic Profiling of Murine Ocular Tissue and the Extracellular Environment

Mass spectrometry-based proteomics provides a robust and reliable method for detecting and quantifying changes in protein abundance among samples, including cells, tissues, organs, and supernatants. Physical damage or inflammation can compromise the ocular surface permitting colonization by bacterial pathogens, commonly Pseudomonas aeruginosa, and the formation of biofilms. The interplay between P. aeruginosa and the immune system at the site of infection defines the host's ability to defend against bacterial invasion and promote clearance of infection. Profiling of the ocular tissue following infection describes the nature of the host innate immune response and specifically the presence and abundance of neutrophil-associated proteins to neutralize the bacterial biofilm. Moreover, detection of unique proteins produced by P. aeruginosa enable identification of the bacterial species and may serve as a diagnostic approach in a clinical setting. Given the emergence and prevalence of antimicrobial resistant bacterial strains, the ability to rapidly diagnose a bacterial infection promoting quick and accurate treatment will reduce selective pressure towards resistance. Furthermore, the ability to define differences in the host immune response towards bacterial invasion enhances our understanding of innate immune system regulation at the ocular surface. Here, we describe murine ocular infection and sample collection, as well as outline protocols for protein extraction and mass spectrometry profiling from corneal tissue and extracellular environment (eye wash) samples. © 2020 Wiley Periodicals LLC. Basic Protocol 1: Murine model of ocular infection Basic Protocol 2: Murine model sample collection Basic Protocol 3: Protein extraction from eye wash Basic Protocol 4: Protein extraction from corneal tissue Basic Protocol 5: Mass spectrometry-based proteomics and bioinformatics from eye wash and corneal tissue samples.

The Role of Elastase in Corneal Epithelial Barrier Dysfunction Caused by Pseudomonas aeruginosa Exoproteins

Purpose

To investigate the role of elastase in corneal epithelial barrier dysfunction caused by the exoproteins secreted by Pseudomonas aeruginosa.

Methods

Exoproteins obtained from Pseudomonas aeruginosa culture supernatant were analyzed by shotgun proteomics approach. In vitro multilayered rabbit corneal epithelial barrier model prepared by air-liquid interface technique (CECs-ALI) were treated with 2 µg/ml exoproteins and/or 8 mM elastase inhibitor. Then the epithelial barrier function was evaluated by transepithelial electrical resistance (TEER) assay and tight junction proteins immunofluorescence. Cell viability and the apoptosis rate were examined by CCK8 assay and flow cytometry. TNF-α, IL-6, IL-8, and IL-1β levels were measured by ELISA. Mice cornea treated with exoproteins and/or elastase inhibitor were evaluated in vivo and in vitro.

Results

Elastase (24.2%) is one of the major components of exoproteins. After 2 µg/ml exoproteins were applied to CECs-ALI for two hours, TEER decreased from 323.2 ±  2.7 to 104 ± 6.8 Ω/cm² (P < 0.001). The immunofluorescence results showed a distinct separation in tight junction and significant degradation of ZO-1 and occludin (P < 0.05). Elastase inhibitor (8 mM) alleviated the decrease in TEER value (234 ± 6.8 Ω cm²) induced by exoproteins. Inhibition of elastase decreased the apoptosis rate of CECs treated with exoproteins from 30.2 ± 3.8% to 7.26 ± 1.3% and the levels of inflammatory factors (P < 0.05). Mice corneal epithelium defect could be induced by exoproteins and protected by elastase inhibitor.

Conclusions

Elastase plays a critical role in corneal epithelial barrier dysfunction caused by Pseudomonas aeruginosa exoproteins via damaging tight junctions. The inhibition of elastase could protect the corneal epithelial barrier via reducing virulence and inflammation.

rpoS-mutation variants are selected in Pseudomonas aeruginosa biofilms under imipenem pressure

Background

Pseudomonas aeruginosa is a notorious opportunistic pathogen causing various types of biofilm-related infections. Biofilm formation is a unique microbial strategy that allows P. aeruginosa to survive adverse conditions such as antibiotic treatment and human immune clearance.

Results

In this study, we experimentally evolved P. aeruginosa PAO1 biofilms for cyclic treatment in the presence of high dose of imipenem, and enriched hyperbiofilm mutants within six cycles in two independent lineages. The competition assay showed that the evolved hyperbiofilm mutants can outcompete the ancestral strain within biofilms but not in planktonic cultures. Whole-genome sequencing analysis revealed the hyperbiofilm phenotype is caused by point mutations in rpoS gene in all independently evolved mutants and the same mutation was found in P. aeruginosa clinical isolates. We further showed that mutation in rpoS gene increased the intracellular c-di-GMP level by turning on the expression of the diguanylate cyclases. Mutation in rpoS increased pyocyanin production and virulence in hyperbiofilm variants.

Conclusion

Here, our study revealed that antibiotic treatment of biofilm-related P. aeruginosa infections might induce a hyperbiofilm phenotype via rpoS mutation, which might partially explain antimicrobial treatment failure of many P. aeruginosa biofilm-related infections.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-021-00655-9.

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.

Mimicking biofilm formation and development: Recent progress in in vitro and in vivo biofilm models

Biofilm formation in living organisms is associated to tissue and implant infections, and it has also been linked to the contribution of antibiotic resistance. Thus, understanding biofilm development and being able to mimic such processes is vital for the successful development of antibiofilm treatments and therapies. Several decades of research have contributed to building the foundation for developing in vitro and in vivo biofilm models. However, no such thing as an "all fit" in vitro or in vivo biofilm models is currently available. In this review, in addition to presenting an updated overview of biofilm formation, we critically revise recent approaches for the improvement of in vitro and in vivo biofilm models.

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.

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.

Magnetic hyperthermia adjunctive therapy for fungi: in vitro studies against Candida albicans

The poor penetration of anti-fungal agents into the cornea through the intact epithelium layer makes it difficult to treat acute fungal corneal infections. Herein, we developed Amphotret (amphotericin B) antifungal drug contained polycaprolactone-Fe₃O₄ (PCL-FO) magnetic nanofibers (MNFs) using the electrospinning technique. These MNFs generate heat in the presence of AC magnetic field (AMF) and release drug upon heating. MNFs were compatible with human mesenchymal stem cells (hMSCs) and HeLa cells, which exhibited unaltered proliferation, ruling out any toxicity from the systems. Hyperthermia induced via MNFs from 42 °C to 50 °C compromised the viability of Candida albicans cells. Further, the efficacy of the systems was increased in the presence of both heat and drug simultaneously in vitro, leading to near 100% loss in viability of C. albicans cells at 50 °C with simultaneous drug release from MNFs. Thus, we propose magnetic hyperthermia as adjunctive therapy for fungal keratitis.

Tasked with a Challenging Objective: Why Do Neutrophils Fail to Battle Pseudomonas aeruginosa Biofilms

Multidrug-resistant (MDR) bacterial infections are a leading cause of mortality, affecting approximately 250,000 people in Canada and over 2 million people in the United States, annually. The lack of efficacy of antibiotic-based treatments is often caused by inability of the drug to penetrate bacterial biofilms in sufficient concentrations, posing a major therapeutic challenge. Here, we review the most recent information about the architecture of Pseudomonas aeruginosa biofilms in vivo and describe how advances in imaging and mass spectroscopy analysis bring about novel therapeutic options and challenge existing dogmas.

Evaluation of prevention and disruption of biofilm in contact lens cases

PURPOSE

The presence of biofilm in the lens case has been shown to be a risk factor for contamination of lenses and consequently microbial keratitis. This study aimed to evaluate effectiveness of solutions for rigid contact lenses in prevention and disruption of biofilm in lens cases and methods for biofilm detection.

METHOD

This study adopted a stepwise approach to evaluate effectiveness of four rigid lens disinfecting solutions against biofilm. These included two polyhexamethylene bigiuanide (PHMB) solutions and a chlorhexidine/PHMB-based solution, as well as a novel povidone-iodine formulation. The presence of biofilm following exposure to the solutions was assessed using both crystal violet (CV) staining and MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) viability assay, taking into account the effect of lens case design. Three lens case designs, conventional flat, large bucket type, and cylindrical cases, were investigated for the ability to trap stain and allow biofilm formation.

RESULTS

Considerable differences were noted between solutions in their ability to prevent and disrupt biofilm (p < 0.001). Lens case design greatly influenced optical density (OD) measurements even in negative controls, as cylindrical cases trapped more stain, increasing OD readings. Correcting for this factor reduced variations, but could not differentiate between residues and biofilm. MTT assay revealed that both povidone-iodine and chlorhexidine-containing solutions could effectively kill > 95% of organisms, whilst PHMB-based solutions were less effective with up to 55% of staphylococci and 41% of Pseudomonas surviving at 24 h.

CONCLUSION

Biofilm can rapidly form in lens cases and may not be killed by disinfecting solutions. Of the solutions tested, none were able to prevent biofilm formation or disrupt established biofilm, but those containing chlorhexidine or povidone iodine were able to penetrate the biofilm and kill organisms. Assessment of biofilm by CV assay may be confounded by lens case design. Whilst CV assay can demonstrate presence of biofilm, this technique should be accompanied by viability assay to determine bactericidal activity.

Corneal Biofilm Plaques: A Novel Clinical Presentation

PURPOSE

To report a novel clinical presentation of corneal biofilms, consisting of formation of superficial and recurrent corneal plaques.

METHODS

Interventional case report. A 9-year-old boy presented with subepithelial, whitish, avascular, and recurrent corneal plaques without any clinical manifestations of active corneal inflammation and/or infection. He had a history of minor ocular trauma; otherwise, his medical history was unremarkable.

RESULTS

An excisional biopsy was performed under topical anesthesia. Histological analysis identified these plaques as clusters of gram-negative bacilli surrounded by an extracellular matrix. Samples were further evaluated with special stains (calcofluor white, Flamingo fluorescent dye, propidium iodide, and Gomori-Grocott) that demonstrated biofilm structures.

CONCLUSIONS

Corneal plaques are a very rare clinical presentation of corneal biofilms that allow prolonged survival of microorganisms even in the absence of prosthetic material and clinical signs or symptoms of corneal active inflammation and/or infection.

Neutrophil Extracellular Traps Confine Pseudomonas aeruginosa Ocular Biofilms and Restrict Brain Invasion

Bacterial biofilm infections are difficult to eradicate because of antibiotic insusceptibility and high recurrence rates. Biofilm formation by Pseudomonas aeruginosa, a leading cause of bacterial keratitis, is facilitated by the bacterial Psl exopolysaccharide and associated with heightened virulence. Using intravital microscopy, we observed that neutrophilic recruitment to corneal infections limits P. aeruginosa biofilms to the outer eye surface, preventing bacterial dissemination. Neutrophils moved to the base of forming biofilms, where they underwent neutrophil extracellular trap formation (NETosis) in response to high expression of the bacterial type-3 secretion system (T3SS). NETs formed a barrier "dead zone," confining bacteria to the external corneal environment and inhibiting bacterial dissemination into the brain. Once formed, ocular biofilms were resistant to antibiotics and neutrophil killing, advancing eye pathology. However, blocking both Psl and T3SS together with antibiotic treatment broke down the biofilm and reversed keratitis, suggesting future therapeutic strategies for this intractable infection.

Frontline Science: Employing enzymatic treatment options for management of ocular biofilm-based infections

Pseudomonas aeruginosa-induced corneal keratitis is a sight-threatening disease. The rise of antibiotic resistance among P. aeruginosa keratitis isolates makes treatment of this disease challenging, emphasizing the need for alternative therapeutic modalities. By comparing the responses to P. aeruginosa infection between an outbred mouse strain (Swiss Webster, SW) and a susceptible mouse strain (C57BL6/N), we found that the inherent neutrophil-killing abilities of these strains correlated with their susceptibility to infection. Namely, SW-derived neutrophils were significantly more efficient at killing P. aeruginosa in vitro than C57BL6/N-derived neutrophils. To interrogate whether the distinct neutrophil killing capacities were dependent on endogenous or exogenous factors, neutrophil progenitor cell lines were generated. The in vitro differentiated neutrophils from either SW or C57BL6/N progenitors retained the differential killing abilities, illustrating that endogenous factors conferred resistance. Consistently, quantitative LC-MS/MS analysis revealed strain-specific and infection-induced alterations of neutrophil proteomes. Among the distinctly elevated proteins in the SW-derived proteomes were α-mannosidases, potentially associated with protection. Inhibition of α-mannosidases reduced neutrophil bactericidal functions in vitro. Conversely, topical application of α-mannosidases reduced bacterial biofilms and burden of infected corneas. Cumulatively, these data suggest novel therapeutic approaches to control bacterial biofilm assembly and improve bacterial clearance via enzymatic treatments.

Characterization of Biofilm Formation by Cronobacter spp. Isolates of Different Food Origin under Model Conditions

Cronobacter spp. are opportunistic human pathogens that cause serious diseases in neonates and immunocompromised people. Owing to their biofilm formation on various surfaces, both their detection and their removal from production plants constitute a major challenge. In this study, food samples were randomly collected in Austria and examined for the presence of Cronobacter spp. Presumptive isolates were identified by a polyphasic approach. Five percent of the samples were positive for C. sakazakii and 2.4% for C. dublinensis. Individual growth of the isolates was characterized based on lag time, growth rate, and generation time. During an incubation period of 6 to 72 h, biofilm formation of 11 selected isolates was quantified under model conditions by a crystal violet staining assay with 96-well plates with different carbon sources (lactose, glucose, maltose, sucrose, and sodium acetate) and NaCl levels and under variable temperature and pH conditions. Biofilm formation was more pronounced at lactose concentrations between 0.25 and 3% compared with 5% lactose, which lead to thinner layers. C. sakazakii isolate C7, isolated from infant milk powder, was the strongest biofilm producer at 10 mM Mg²⁺ and 5 mM Mn²⁺, 0.5% sodium acetate, at pH levels between 7 and 9 at 37°C for 24 h. C. sakazakii strain C6 isolated from a plant air filter was identified as a moderate biofilm former and C. sakazakii strain DSM 4485, a clinical isolate, as a weak biofilm former. Based on PCR detection, genes bcsA, bcsB, and bcsG encoding for cellulose could be identified as markers for biofilm formation. Isolates carrying bcsA and bcsB showed significantly stronger biofilm formation than isolates without these genes ( P < 0.05), in strong correlation with the results obtained in the crystal violet assay. Further investigations using confocal laser scanning microscopy revealed that extracellular polymeric substances and glycocalyx secretions were the dominating components of the biofilms and that the viable fraction of bacteria in the biofilm decreased over time.

Development of a Broad-Spectrum Antimicrobial Combination for the Treatment of Staphylococcus aureus and Pseudomonas aeruginosa Corneal Infections

Staphylococcus aureus and Pseudomonas aeruginosa are two of the most common causes of bacterial keratitis and corresponding corneal blindness. Accordingly, such infections are predominantly treated with broad-spectrum fluoroquinolones, such as moxifloxacin. Yet, the rising fluoroquinolone resistance has necessitated the development of alternative therapeutic options. Herein, we describe the development of a polymyxin B-trimethoprim (PT) ophthalmic formulation containing the antibiotic rifampin, which exhibits synergistic antimicrobial activity toward a panel of contemporary ocular clinical S. aureus and P. aeruginosa isolates, low spontaneous resistance frequency, and in vitro bactericidal kinetics and antibiofilm activities equaling or exceeding the antimicrobial properties of moxifloxacin. The PT plus rifampin combination also demonstrated increased efficacy in comparison to those of either commercial PT or moxifloxacin in a murine keratitis model of infection, resulting in bacterial clearance of 70% in the animals treated. These results suggest that the combination of PT and rifampin may represent a novel antimicrobial agent in the treatment of bacterial keratitis.

Repurposing the anticancer drug cisplatin with the aim of developing novel Pseudomonas aeruginosa infection control agents

Antibiotic resistance threatens effective treatment of microbial infections globally. This situation has spurred the hunt for new antimicrobial compounds in both academia and the pharmaceutical industry. Here, we report how the widely used antitumor drug cisplatin may be repurposed as an effective antimicrobial against the nosocomial pathogen Pseudomonas aeruginosa. Cisplatin was found to effectively kill strains of P. aeruginosa. In such experiments, transcriptomic profiling showed upregulation of the recA gene, which is known to be important for DNA repair, implicating that cisplatin could interfere with DNA replication in P. aeruginosa. Cisplatin treatment significantly repressed the type III secretion system (T3SS), which is important for the secretion of exotoxins. Furthermore, cisplatin was also demonstrated to eradicate in vitro biofilms and in vivo biofilms in a murine keratitis model. This showed that cisplatin could be effectively used to eradicate biofilm infections which were otherwise difficult to be treated by conventional antibiotics. Although cisplatin is highly toxic for humans upon systemic exposure, a low toxicity was demonstrated with topical treatment. This indicated that higher-than-minimal inhibitory concentration (MIC) doses of cisplatin could be topically applied to treat persistent and recalcitrant P. aeruginosa infections.

Designed Host Defense Peptides for the Treatment of Bacterial Keratitis

Purpose

To limit corneal damage and potential loss of vision, bacterial keratitis must be treated aggressively. Innovation in antimicrobials is required due to the need for empirical treatment and the rapid emergence of bacterial resistance. Designed host defense peptides (dHDPs) are synthetic analogues of naturally occurring HDPs, which provide defense against invading pathogens. This study investigates the use of novel dHDPs for the treatment of bacterial keratitis.

Methods

The minimum inhibitory concentrations (MICs) were determined for dHDPs on both Gram-positive and -negative bacteria. The minimum biofilm eradication concentrations (MBEC) and in vitro time-kill assays were determined. The most active dHDP, RP444, was evaluated for propensity to induce drug resistance and therapeutic benefit in a murine Pseudomonas aeruginosa keratitis model.

Results

Designed HDPs were bactericidal with MICs ranging from 2 to >64 μg/mL and MBEC ranging from 6 to 750 μg/mL. In time-kill assays, dHDPs were able to rapidly reduce bacterial counts upon contact with as little as 2 μg/mL. RP444 did not induce resistance after repeated exposure of P. aeruginosa to subinhibitory concentrations. RP444 demonstrated significant efficacy in a murine model of bacterial keratitis as evidenced by a significant dose-dependent decrease in ocular clinical scores, a significantly reduced bacterial load, and substantially decreased inflammatory cell infiltrates.

Conclusions

Innovative dHDPs demonstrated potent antimicrobial activity, possess a limited potential for development of resistance, and reduced the severity of murine P. aeruginosa keratitis. These studies demonstrate that a novel dHDP may have potential to treat patients with sight-threatening bacterial keratitis.

Discovery of novel antimycobacterial drug therapy in biofilm of pathogenic nontuberculous mycobacterial keratitis

PURPOSE

The potential of slow-growing mycobacteria to form biofilms in human tissues contributes to the problem of establishing an effective treatment strategy. The purpose of this study was to examine new antibiotic strategies to enhance current treatment options for these infections.

METHODS

Sensitivities of Mycobacterium fortuitum ATCC 49404 and Mycobacterium chelonae ATCC 35752 were evaluated for different antimicrobials singly and in combination using broth microdilution and FICI (Fractional Inhibitory Concentration Index) synergy screening. Anti-biofilm effects were evaluated in an 8-well chamber slide biofilm model. The efficacy of a new treatment strategy was validated using the novel neutropenic mouse keratitis model and monitored by slit-lamp microscopy, confocal microscopy, and colony forming unit measurements.

RESULTS

We reported the very first evidence that these organisms develop corneal biofilms by the accumulation of extracellular DNA (eDNA) and the presence of microcolonies using a novel mycobacterial neutropenic mouse keratitis model. The combination of amikacin and gatifloxacin or besifloxacin was more effective than the current gold-standard drug, amikacin, and we developed a novel treatment strategy (amikacin + gatifloxacin + DNase), the destruction of biofilm matrix component, eDNA, which increased the efficacy of the new antibiotic combination for treating mycobacterial infection in in vitro (P = 0.002) and in vivo (P = 0.001) compared to its respective control.

CONCLUSION

Biofilms have a role in mycobacterial keratitis leading to poor treatment outcomes in clinical practice and the use of combination therapy (amikacin + gatifloxacin + DNase) could be a useful new treatment option.

A proof-of-concept model for the identification of the key events in the infection process with specific reference to Pseudomonas aeruginosa in corneal infections

BACKGROUND

It is a common medical practice to characterise an infection based on the causative agent and to adopt therapeutic and prevention strategies targeting the agent itself. However, from an epidemiological perspective, exposure to a microbe can be harmless to a host as a result of low-level exposure or due to host immune response, with opportunistic infection only occurring as a result of changes in the host, pathogen, or surrounding environment.

METHODS

We have attempted to review systematically the key host, pathogen, and environmental factors that may significantly impact clinical outcomes of exposure to a pathogen, using Pseudomonas aeruginosa eye infection as a case study.

RESULTS AND DISCUSSION

Extended contact lens wearing and compromised hygiene may predispose users to microbial keratitis, which can be a severe and vision-threatening infection. P. aeruginosa has a wide array of virulence-associated genes and sensing systems to initiate and maintain cell populations at the corneal surface and beyond. We have adapted the well-known concept of the epidemiological triangle in combination with the classic risk assessment framework (hazard identification, characterisation, and exposure) to develop a conceptual pathway-based model that demonstrates the overlapping relationships between the host, the pathogen, and the environment; and to illustrate the key events in P. aeruginosa eye infection.

CONCLUSION

This strategy differs from traditional approaches that consider potential risk factors in isolation, and hopefully will aid the identification of data and models to inform preventive and therapeutic measures in addition to risk assessment. Furthermore, this may facilitate the identification of knowledge gaps to direct research in areas of greatest impact to avert or mitigate adverse outcomes of infection.

Biofilms of Pathogenic Nontuberculous Mycobacteria Targeted by New Therapeutic Approaches

Microbial infections of the cornea are potentially devastating and can result in permanent visual loss or require vision-rescuing surgery. In recent years, there has been an increasing number of reports on nontuberculous mycobacterial infections of the cornea. Challenges to the management of nontuberculous mycobacterial keratitis include delayed laboratory detection, low index of clinical suspicion, poor drug penetration, slow response to therapy, and prolonged use of antibiotic combinations. The ability of nontuberculous mycobacteria to evade the host immune response and the ability to adhere and to form biofilms on biological and synthetic substrates contribute to the issue. Therefore, there is an urgent need for new antimicrobial compounds that can overcome these problems. In this study, we evaluated the biofilm architectures for Mycobacterium chelonae and Mycobacterium fortuitum in dynamic flow cell chamber and 8-well chamber slide models. Our results showed that mycobacterial biofilms were quite resistant to conventional antibiotics. However, DNase treatment could be used to overcome biofilm resistance. Moreover, we successfully evaluated a new antimicrobial compound (AM-228) that was effective not only for planktonic mycobacterial cells but also for biofilm treatment and was compared favorably with the most successful “fourth-generation” fluoroquinolone, gatifloxacin. Finally, a new treatment strategy emerged: a combination of DNase with an antibiotic was more effective than an antibiotic alone.