Consensus and controversies in the science of endophthalmitis management: Basic research and clinical perspectives

Infectious endophthalmitis is a severe intraocular infection caused by bacteria, or less commonly by fungi. It can occur after penetrating eye procedures, trauma, or the spread of infection from contiguous structures or via emboli from distant organs. Because of the time-critical nature of the treatment, endophthalmitis is treated with the clinical diagnosis and modified by the microbiological report of the intraocular contents. The current strategy for managing endophthalmitis relies on pre-clinical literature, case series, and one large multi-center randomized clinical trial on post-cataract surgery endophthalmitis. Culture-susceptibility of the microorganisms from undiluted vitreous guides the definitive treatment in non-responsive cases. Strategies to reduce the incidence of endophthalmitis after penetrating eye procedures have been developed concurrently with refined means of treatment. Despite these advances, outcomes remain poor for many patients. Although consensus articles have been published on managing endophthalmitis, treatment patterns vary, and controversies remain. These include (1) the use of newer methods for early and precise microbiological diagnosis; (2) the choice of intravitreal antibiotics; (3) the need for systemic therapy; (4) early and complete vitrectomy. Here, we review the current consensus and address controversies in diagnosing and managing endophthalmitis. This review is intended to familiarize physicians and ophthalmologists with different aspects of endophthalmitis management to make informed decisions.

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.

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.

Acquisition of Daptomycin Resistance by Enterococcus faecium Confers Collateral Sensitivity to Glycopeptides

Daptomycin is a last-line antibiotic used in the treatment of multidrug-resistant Enterococcus faecium infections. Alarmingly, daptomycin-resistant E. faecium isolates have emerged. In this study, we investigated the evolution and mechanisms of daptomycin resistance in clinical E. faecium isolates and the corresponding acquisition of collateral sensitivity (CS) as an evolutionary trade-off. We evolved daptomycin resistance in six daptomycin-susceptible E. faecium isolates to obtain daptomycin-resistant mutants. The six E. faecium strains successfully acquired high-level resistance to daptomycin in vitro, but this led to fitness costs in terms of growth, in vitro competition, and virulence. Mutations in liaFSR, yycFG, and cls; increased surface positive charge; thicker cell walls; and elevated expression of dltABCD and tagGH were observed in daptomycin-resistant mutants. Surprisingly, we observed the emergence of CS in SC1762 isolates after the induction of daptomycin resistance. Compared with parental strains, the SC1174-D strain (i.e., daptomycin-resistant mutant of SC1174; non-CS) showed significantly upregulated expression of the vanA gene cluster. However, in SC1762-D (i.e., daptomycin-resistant mutant of SC1762), all vanA cluster genes except the vanX gene were obviously downregulated. Further in silico analyses revealed that an IS1216E-based composite transposon was generated in SC1762-D, and it disrupted the vanH gene, likely affecting the structure and expression of the vanA gene cluster and resulting in resensitization to glycopeptides. Overall, this study reports a novel form of CS between daptomycin and glycopeptides in E. faecium. Further, it provides a valuable foundation for developing effective regimens and sequential combinations of daptomycin and glycopeptides against E. faecium.

Evaluation of Combined Ciprofloxacin and azithromycin free and nano formulations to control biofilm producing Pseudomonas aeruginosa isolated from burn wounds

BACKGROUND

Nanoparticles are becoming increasingly important against resistant superbugs including Pseudomonas aeruginosa infections.

AIMS

Exploration of Azithromycin as an adjunctive therapy to Ciprofloxacin for treatment of P. aeruginosa infections. Also, preparation of Ciprofloxacin-Azithromycin nanoparticles on chitosan nanocarrier (Cipro-AZM-CS) and assessment of its antimicrobial effect in vitro and in vivo.

METHODS

Detection of biofilm production and biofilm-specific antibiotic resistance ndvB and tssC1 genes was attempted. Minimal inhibitory concentration (MIC) and Minimum biofilm eradication concentration (MBEC) were done in vitro for assessment of P. aeruginosa planktonic and biofilm forms eradication, respectively. In In vivo study, Cipro-AZM-CS and free form were used to evaluate survival rate, wound contraction and bacterial load in mice after third degree burn.

RESULTS

All isolates were positive for biofilm production and ndvB and tssC1 genes. Majority of isolates (37, 74%) were extensively drug resistant. In the planktonic state, MIC values of Cipro-AZM free and CS forms were significantly lower than free Cipro MIC (P = 0.015 and P < 0.001 respectively). Also, Cipro-AZM free and CS MBEC values were significantly lower than that of free Cipro (P < 0.010 and P < 0.001 respectively). Furthermore, The MIC and MBEC values of free Cipro-AZM decreased significantly when challenged with Cipro-AZM-CS (P = 0.009 and P < 0.001 respectively). In vivo study combined free and Cipro-AZM-CS treated subgroups showed 100% mice survival with early resolution of infection and wound contraction (75%, 77.5% respectively) VS 45% for Cipro CS (P < 0.001).

CONCLUSION

Combined free and Cipro-AZM-CS showed promising results in vitro and in vivo overcoming high resistance of biofilm producing P. aeruginosa.

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.

Characterization of Putative Virulence Factors of Pseudomonas aeruginosa Strain RBS Isolated from a Saltern, Tunisia: Effect of Metal Ion Cofactors on the Structure and the Activity of LasB

Pseudomonas aeruginosa is a ubiquitous Gram-negative bacterium able to survive in diverse environments such as soil, plants, freshwater, and seawater. P. aeruginosa can be an opportunistic pathogen to humans when their immune system is deficient. Its pathogenicity may be linked to the production of virulence factors. We isolated P. aeruginosa strain RBS from the saltern of Sfax in Tunisia. In this study, we characterized the halotolerance, antibiotic susceptibility, and some virulence factors of strain RBS. High NaCl concentrations inhibited growth and motility. However, biofilm formation was enhanced to protect bacteria against salt stress. Among the 18 antibiotics tested, quinolones and tetracycline showed a significant inhibitory effect on growth, motility, and biofilm formation of strain RBS. β-Lactams, however, did not have any inhibitory effect on neither bacterial growth nor motility. In some cases, resistance was due, in part, to biofilm formation. We also showed that RBS produces two proteases, LasB and AprA, which have been shown to be implicated in host infection. LasB was further characterized to study the role of metal ions in enzyme stability. It possesses two distinct metal ion-binding sites coordinating a calcium and a zinc ion. The effect of metal ion chelation was evaluated as well as substitutions of residues involved in metal ion binding. Impairing metal ion binding of LasB led to a loss of activity and a sharp decrease of stability. Our findings suggest that the binding of both metal ions is interdependent as the two metal ions' binding sites are linked via a hydrogen bond network.

Quercetin inhibits Pseudomonas aeruginosa biofilm formation via the vfr-mediated lasIR system

Pseudomonas aeruginosa is one of the most common opportunistic pathogens that cause biofilm-associated infections. Biofilm formation is partially regulated by the quorum sensing (QS) system, and quercetin can inhibit QS, biofilm formation and virulence factors. We therefore speculated that quercetin would inhibit the formation of P. aeruginosa biofilm via the QS system. In this study, we successfully constructed lasI, rhlI and lasI/rhlI gene-knockout strains. The knockout of the lasI and lasI/rhlI genes resulted in decreases in adhesion, biofilm formation, swarming motility and the expression of biofilm-associated genes, whereas deletion of the rhlI gene had no obvious influence on these biofilm-related indicators with the exception of the swarming motility. After treatment with quercetin, the lasI- and lasI/rhlI-mutant strains exhibited increased adhesion, biofilm formation, swarming motility and biofilm-associated gene expression compared with the control group. However, quercetin still exerted an inhibitory effect on these physiological factors and the biofilm-associated gene expression in the rhlI-mutant strain. The knockout of QS genes reduced the production of pyocyanin and protease activity, but after the virulence factors of the QS-mutant strains treated with quercetin showed almost no differences compared with those of the control group. In addition, quercetin could significantly inhibit vfr gene expression regardless of the presence of QS genes. The results indicated that quercetin might inhibit the lasIR system through the vfr gene and ultimately the formation of P. aeruginosa biofilms.

Meta-Analysis of Biofilm Formation, Antibiotic Resistance Pattern, and Biofilm-Related Genes in Pseudomonas aeruginosa Isolated from Clinical Samples

Resistant microorganisms such as Pseudomonas aeruginosa grow by developing biofilms in hospitals. We aimed to investigate the biofilm formation and the frequencies of biofilm-related genes and their associations with antibiotic resistance pattern in P. aeruginosa isolated from Iranians' clinical samples. This review was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. We conducted a systematic literature search in scientific databases using medical subject heading terms, including "Pseudomonas aeruginosa," "biofilm formation," "biofilm-related genes," "antibiotic resistance," and "prevalence," to obtain related articles published from 1st January, 2000, to 30th March, 2019. The studies reporting the prevalence of biofilm formation, the frequencies of biofilm-related genes, and the antibiotic resistance pattern in P. aeruginosa retrieved from Iranian patients were included. Meta-analysis was performed using the Comprehensive Meta-Analysis software. The pooled rate of biofilm formation was calculated as 86.5% (95% confidence interval [CI]: 79-91.6). The combined frequencies of strong, moderate, and weak biofilms were 51% (95% CI: 37.4-64.4), 29.2% (95% CI: 20.9-39.1), and 25.4% (95% CI: 11.5-47.2), respectively. The pooled prevalence of laslR, algD, algU, ppyR, and pelF genes were 93.6% (95% CI: 88.1-96.6), 91.4% (95% CI: 80.8-96.4), 89.3% (95% CI: 85.2-92.3), 98.7% (95% CI: 96.5-99.6), and 93% (95% CI: 82.7-97.3), respectively. The highest combined antibiotic resistance rates of P. aeruginosa isolates were against piperacillin/tazobactam (90%). This study showed that biofilm formation was higher in multidrug-resistant (MDR) P. aeruginosa than non-MDRs. A significant correlation was observed between biofilm formation and antibiotic resistance in 50% of studies included in this review.

Pse-T2, an Antimicrobial Peptide with High-Level, Broad-Spectrum Antimicrobial Potency and Skin Biocompatibility against Multidrug-Resistant Pseudomonas aeruginosa Infection

Pseudin-2, isolated from the frog Pseudis paradoxa, exhibits potent antibacterial activity but also cytotoxicity. In an effort to develop clinically applicable antimicrobial peptides (AMPs), we designed pseudin-2 analogs with Lys substitutions, resulting in elevated amphipathic α-helical structure and cationicity. In addition, truncated analogs of pseudin-2 and Lys-substituted peptides were synthesized to produce linear 18-residue amphipathic α-helices, which were further investigated for their mechanism and functions. These truncated analogs exhibited higher antimicrobial activity and lower cytotoxicity than pseudin-2. In particular, Pse-T2 showed marked pore formation, permeabilization of the outer/inner bacterial membranes, and DNA binding. Fluorescence spectroscopy and scanning electron microscopy showed that Pse-T2 kills bacterial cells by disrupting membrane integrity. In vivo, wounds infected with multidrug-resistant (MDR) Pseudomonas aeruginosa healed significantly faster when treated with Pse-T2 than did untreated wounds or wounds treated with ciprofloxacin. Moreover, Pse-T2 facilitated infected-wound closure by reducing inflammation through suppression of interleukin-1β (IL-1β), IL-6, and tumor necrosis factor alpha (TNF-α). These data suggest that the small antimicrobial peptide Pse-T2 could be useful for future development of therapeutic agents effective against MDR bacterial strains.