Shifting Trends in Bacterial Keratitis in Toronto

Pediatric bacterial keratitis: clinical features, causative organisms, and outcome during a 13-year study period

OBJECTIVE

To review the clinical features, causative organisms, complications, and outcomes of patients with pediatric bacterial keratitis at a tertiary care eye hospital.

METHODS

We conducted a retrospective study at a tertiary care eye centre on clinically diagnosed pediatric patients with bacterial keratitis between 2007 and 2019. Poor outcomes were labelled if any of the following were present: final best-corrected visual acuity worse than 20/200, a drop in best-corrected visual acuity by 1 line or more, perforated corneas, endophthalmitis, and graft failure.

RESULTS

The study included 43 cases of bacterial keratitis. Female and male patients represented 60.5% and 39.5% of the sample, respectively, with a mean age of 9.3 ± 5.9 years. The rate of culture positivity was 60.5%. The most common causative organisms were coagulase-negative Staphylococcus (23.1%), Pseudomonas (23.1%), and Streptococcus pneumoniae (19.2%). Culture-positive bacterial keratitis was associated with infiltrates ≥2 mm (p = 0.039), as determined by the results of multivariate analysis. Gram-positive and gram-negative bacteria exhibited 100% sensitivity to the tested fluoroquinolones. Complications included visually significant scars (55.8%), cataracts (14.0%), perforations (9.3%), corneal neovascularization (7.0%), nonhealing epithelial defects (7.0%), and endophthalmitis (4.7%). Corneal perforation was associated with the development of endophthalmitis (p < 0.001). On multivariate analysis, the only factor associated with a poor outcome was poor presenting visual acuity (p = 0.020).

CONCLUSION

Gram-positive bacteria were the most common cause of pediatric microbial keratitis. Positive cultures were associated with larger infiltrates. The only adverse prognostic factor was poor presenting vision.

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.

Trends in antibiotic resistance in ocular samples in a tertiary eye centre in Saudi Arabia in 2003-2019

OBJECTIVE

The aim of this study was to analyze the antibiotic resistance in ocular samples over a 16-year period.

METHODS

This was a retrospective cohort study conducted at King Khaled Eye Specialist Hospital, Riyadh, Saudi Arabia (2003-2019). The study included corneal and conjunctival swabs and aqueous and vitreous samples.

RESULTS

Coagulase-negative staphylococci exhibited a significant trend of increasing resistance over time to erythromycin (p < 0.001), oxacillin (p < 0.001), fusidic acid (p < 0.001), and moxifloxacin (p = 0.003). Staphylococcus aureus also showed a significant increase in oxacillin (p = 0.001), ofloxacin (p = 0.003), and moxifloxacin (p = 0.001) resistance patterns. Streptococcus pneumoniae demonstrated a significant increase in resistance to erythromycin (p = 0.01) and ofloxacin, which jumped from 0.80% in 2003 to 80% in 2019 (p = 0.015). No statistically significant increase in antibiotic resistance trend was observed for Pseudomonas.

CONCLUSIONS

An increasing antibiotic resistance pattern was demonstrated, particularly among gram-positive organisms. Such findings warrant revision of the common ocular antibiotic prescribing strategy and consideration of alternative antibiotics.

Reimagining the Past: A Future for Antibiotic Drug Discovery in Ophthalmology

ABSTRACT

Antibiotic resistance has emerged as a critical threat for the treatment of bacterial ocular infections. To address the critical need for novel therapeutics, antibiotic drug repurposing holds significant promise. As such, examples of existing FDA-approved drugs currently under development for new applications, novel combinations, and improved delivery systems are discussed.

Multifunctional Polymer Vesicles for Synergistic Antibiotic-Antioxidant Treatment of Bacterial Keratitis

As an acute ophthalmic infection, bacterial keratitis (BK) can lead to severe visual morbidity, such as corneal perforation, intraocular infection, and permanent corneal opacity, if rapid and effective treatments are not available. In addition to eradicating pathogenic bacteria, protecting corneal tissue from oxidative damage and promoting wound healing by relieving inflammation are equally critical for the efficient treatment of BK. Besides, it is very necessary to improve the bioavailability of drugs by enhancing the ocular surface adhesion and corneal permeability. In this investigation, therefore, a synergistic antibiotic-antioxidant treatment of BK was achieved based on multifunctional block copolymer vesicles, within which ciprofloxacin (CIP) was simultaneously encapsulated during the self-assembly. Due to the phenylboronic acid residues in the corona layer, these vesicles exhibited enhanced muco-adhesion, deep corneal epithelial penetration, and bacteria-targeting, which facilitated the drug delivery to corneal bacterial infection sites. Additionally, the abundant thioether moieties in the hydrophobic membrane enabled the vesicles to both have ROS-scavenging capacity and accelerated CIP release at the inflammatory corneal tissue. In vivo experiments on a mice model demonstrated that the multifunctional polymer vesicles achieved efficient treatment of BK, owing to the enhanced corneal adhesion and penetration, bacteria targeting, ROS-triggered CIP release, and the combined antioxidant-antibiotic therapy. This synergistic strategy holds great potential in the treatment of BK and other diseases associated with bacterial infections.

Molecular and Phenotypic Characterization of Ocular Methicillin-Resistant Staphylococcus epidermidis Isolates in Taiwan

Purpose

Staphylococcus epidermidis, a commensal, has emerged as an important opportunistic pathogen, particularly methicillin-resistant S. epidermidis (MRSE). The mechanism behind this transformation remains unclear. This study aimed to investigate the molecular and phenotypic characteristics of MRSE isolated from healthy conjunctiva and ocular infections.

Methods

We collected MRSE isolates from two groups: healthy conjunctiva from patients undergoing cataract surgeries and ocular infections at our hospital. Genotypic analysis included pulsed-field gel electrophoresis (PFGE), multilocus sequence typing (MLST), staphylococcal cassette chromosome mec (SCCmec), and biofilm-related genes (icaA, aap, and bhp). Additionally, phenotypic data on biofilm production and antibiotic susceptibility were recorded.

Results

A total of 86 isolates, including 42 from healthy conjunctiva and 44 from ocular infections, were analyzed. MLST identified 21 sequence types (STs), with ST59 being the most frequent (n = 33, 39.5%), followed by ST130 (n = 10, 11.6%), ST57 (n = 6, 7.0%), and ST2 (n = 6, 7.0%). All isolates were categorized in 23 PFGE types, and SCCmec IV was the most prevalent SCCmec type (n = 52, 60.5%). The two sources of isolates exhibited overlapping molecular types and phenotypic traits, although the ocular infection isolates exhibited significantly higher multidrug resistance compared to healthy conjunctiva isolates (P = 0.032). When contrasting ST59 with non-ST59, ST59 displayed a significantly higher presence of aap (100%) and bhp (69.7%) while lacking icaA (0%). ST59 also showed lower susceptibility to fluoroquinolones compared to non-ST59 (42.4%-54.5% vs. 75.5%-83.0%; P < 0.01).

Conclusions

MRSE isolates from healthy conjunctiva and ocular infections demonstrated a degree of resemblance. Specific strains, notably ST59, exhibited distinctive characterizations.

Ocular Bacterial Infections: A Ten-Year Survey and Review of Causative Organisms Based on the Oklahoma Experience

Ocular infections can be medical emergencies that result in permanent visual impairment or blindness and loss of quality of life. Bacteria are a major cause of ocular infections. Effective treatment of ocular infections requires knowledge of which bacteria are the likely cause of the infection. This survey of ocular bacterial isolates and review of ocular pathogens is based on a survey of a collection of isolates banked over a ten-year span at the Dean McGee Eye Institute in Oklahoma. These findings illustrate the diversity of bacteria isolated from the eye, ranging from common species to rare and unique species. At all sampled sites, staphylococci were the predominant bacteria isolated. Pseudomonads were the most common Gram-negative bacterial isolate, except in vitreous, where Serratia was the most common Gram-negative bacterial isolate. Here, we discuss the range of ocular infections that these species have been documented to cause and treatment options for these infections. Although a highly diverse spectrum of species has been isolated from the eye, the majority of infections are caused by Gram-positive species, and in most infections, empiric treatments are effective.

Bacterial Keratitis: Clinical Features, Causative Organisms, and Outcome During a 13-year Study Period

PURPOSE

This study aimed to review clinical features, causative organisms, complications, and outcome of bacterial keratitis cases at a tertiary eye hospital.

METHODS

A retrospective study was conducted on clinically diagnosed bacterial keratitis cases from 2007 to 2019. Poor outcome was flagged if any of the following was identified: final visual acuity (VA) worse than 20/200, decrease in VA (1 line or worse compared with presenting VA), corneal perforation, endophthalmitis, failed graft, or cases requiring enucleation or evisceration.

RESULTS

The study included 263 cases of bacterial keratitis with 169 cases (64.3%) of culture-positive bacterial keratitis. Gram-positive bacteria were found to be the causative organism in 106 cases (62.8%). The most common types were coagulase-negative staphylococci (23.1%) and Pseudomonas (23.1%). Culture-positive bacterial keratitis was associated with the development of anterior chamber reaction (≥1+) on multivariate analysis [adjusted odds ratio (OR): 3.03, confidence interval (CI): 1.23-7.45, P = 0.016]. The complications that occurred in the current cohort included visually significant scar (64.7%), perforation (10.8%), cataract (8.8%), nonhealing epithelial defects (8.0%), corneal neovascularization (4.9%), endophthalmitis (4.6%), and hypotony (1.5%). On multivariate analysis, diabetes mellitus (adjusted OR: 3.51, CI: 1.59-7.76, P = 0.002), poor presenting best-corrected VA (adjusted OR: 3.95, CI 1.96-7.96, P < 0.001), and positive cultures (adjusted OR: 2.36, CI: 1.11-5.00, P = 0.025) were associated with poor outcome.

CONCLUSIONS

Culture-negative keratitis had less severe infection and better outcomes when compared to culture-positive bacterial keratitis. Factors associated with poor outcome included diabetes, poor presenting VA, and positive cultures.

Advances in Nanogels for Topical Drug Delivery in Ocular Diseases

Nanotechnology has accelerated the development of the pharmaceutical and medical technology fields, and nanogels for ocular applications have proven to be a promising therapeutic strategy. Traditional ocular preparations are restricted by the anatomical and physiological barriers of the eye, resulting in a short retention time and low drug bioavailability, which is a significant challenge for physicians, patients, and pharmacists. Nanogels, however, have the ability to encapsulate drugs within three-dimensional crosslinked polymeric networks and, through specific structural designs and distinct methods of preparation, achieve the controlled and sustained delivery of loaded drugs, increasing patient compliance and therapeutic efficiency. In addition, nanogels have higher drug-loading capacity and biocompatibility than other nanocarriers. In this review, the main focus is on the applications of nanogels for ocular diseases, whose preparations and stimuli-responsive behaviors are briefly described. The current comprehension of topical drug delivery will be improved by focusing on the advances of nanogels in typical ocular diseases, including glaucoma, cataracts, dry eye syndrome, and bacterial keratitis, as well as related drug-loaded contact lenses and natural active substances.

Urgent unmet needs in the care of bacterial keratitis: An evidence-based synthesis

Bacterial corneal infections, or bacterial keratitis (BK), are ophthalmic emergencies that frequently lead to irreversible visual impairment. Though increasingly recognized as a major cause of global blindness, modern paradigms of evidence-based care in BK have remained at a diagnostic and therapeutic impasse for over half a century. Current standards of management - based on the collection of corneal cultures and the application of broad-spectrum topical antibiotics - are beset by important yet widely underrecognized limitations, including approximately 30% of all patients who will develop moderate to severe vision loss in the affected eye. Though recent advances have involved a more clearly defined role for adjunctive topical corticosteroids, and novel therapies such as corneal crosslinking, overall progress to improve patient and population-based outcomes remains incommensurate to the chronic morbidity caused by this disease. Recognizing that the care of BK is guided by the clinical axiom, "time equals vision", this chapter offers an evidence-based synthesis for the clinical management of these infections, underscoring critical unmet needs in disease prevention, diagnosis, and treatment.

The epidemiology of infectious keratitis

Infectious keratitis is a rare but potentially severe sight-threatening disease, associated with considerable societal burden, cost and morbidity. This review summarises the most recent evidence for the incidence, risk factors and impact of disease, all of which vary widely according to region, access to health care, socioeconomic and environmental factors, predisposing conditions and causative organisms. The frequency and societal impact of infectious keratitis are significantly higher in low-income countries. In non-viral infectious keratitis, bacterial causes predominate in most regions. Fungi, particularly linked with agricultural trauma, are more frequently associated with infectious keratitis in low-income regions, particularly in India and certain African countries. The disease impact is compounded by poverty and limited access to services and treatment. Early diagnosis, access to appropriate treatment, prophylaxis in ocular trauma, availability of eye protection, awareness of risk factors may be associated with reduced disease severity and vision loss. Evidence for the incidence and burden of disease is lacking in certain regions and well-designed epidemiological studies to identify independent risk factors for the disease and those associated with more severe outcomes may better identify causation and guide resource allocation and preventative strategies.

Entropy-Mediated High-Entropy MXenes Nanotherapeutics: NIR-II-Enhanced Intrinsic Oxidase Mimic Activity to Combat Methicillin-Resistant Staphylococcus Aureus Infection

Bacterial infections, such as bacterial keratitis (BK) and subcutaneous abscess, pose significant challenges to global healthcare. Innovative and new antibacterial agents and antibacterial strategies are in demand to control infections in this era of high drug resistance. Nanotechnology is gradually emerging as an economically feasible and effective anti-infection treatment. High-entropy MXenes (HE MXenes) are used to confer desirable properties with exposed active sites to high-entropy atomic layers, whose potential application in the field of biomedicine remains to be explored. Herein, monolayer HE MXenes are fabricated by implementing transition metals with high entropy and low Gibbs free energy to fill the gap in the biocatalytic performance of non-high-entropy MXenes. HE MXenes are endowed with extremely strong oxidase mimic activity (K_m = 0.227 mm) and photothermal conversion efficiency (65.8%) in the second near-infrared (NIR-II) biowindow as entropy increases. Subsequently, HE MXenes realize NIR-II-enhanced intrinsic oxidase mimic activity for killing methicillin-resistant Staphylococcus aureus and rapidly removing the biofilm. Furthermore, HE MXenes can effectively treat BK and subcutaneous abscess infection induced by methicillin-resistant Staphylococcus aureus as nanotherapeutic agents with minuscule side effects. Overall, monolayer HE MXenes demonstrate promising clinical application potential in the treatment of drug-resistant bacterial infections and promote the healing of infected tissues.

Antimicrobial resistance in topical treatments for microbial keratitis: protocol for a systematic review and meta-analysis

INTRODUCTION

There is evidence for increased resistance against the antimicrobials used to treat keratitis. This review aims to provide global and regional prevalence estimates of antimicrobial resistance in corneal isolates and the range of minimum inhibitory concentrations (MIC) with their associated resistance breakpoints.

METHODS AND ANALYSIS

We report this protocol following Preferred Reporting Items for Systematic Review and Meta-Analyses Protocols guidelines. We will conduct an electronic bibliographic search in MEDLINE, EMBASE, Web of Science and the Cochrane Library. Eligible studies will report in any language data for the resistance or MIC for antimicrobials against bacterial, fungal or amoebic organisms isolated from suspected microbial keratitis. Studies that only report on viral keratitis will not be included. There will be no time restrictions on the date of publication. Screening for eligible studies, assessment of risk of bias and data extraction will be conducted by two reviewers independently, using predefined inclusion criteria and prepiloted data extraction forms. We will resolve disagreements between the reviewers by discussion and, if required, a third (senior) reviewer will arbitrate. We will assess the risk of bias using a tool validated in prevalence studies. The certainty of the evidence will be assessed using the Grades of Recommendation, Assessment, Development and Evaluation approach. Pooled proportion estimates will be calculated using a random-effects model. Heterogeneity will be assessed using the I2 statistic. We will explore differences between Global Burden of Disease regions and temporal trends.

ETHICS APPROVAL AND DISSEMINATION

Ethics approval is not required as this is a protocol for a systematic review of published data. The findings of this review will be published in an open-access, peer-reviewed journal.

PROSPERO REGISTRATION NUMBER

CRD42023331126.

Novel Map Biopsy Technique to Define the Extent of Infection Before Penetrating Keratoplasty for Acanthamoeba Keratitis

PURPOSE

The purpose of this study was to report a novel approach of prepenetrating keratoplasty (PKP) corneal map biopsies to define the extent of Acanthamoeba cyst infiltration in recalcitrant Acanthamoeba keratitis.

METHODS

Corneal map biopsies were performed 1 week before PKP. Four biopsies, 1 from each peripheral corneal quadrant, were obtained to delineate the extent of microscopic infection. Histological results of these map biopsies were used to determine the size and location of the subsequent PKP.

RESULTS

In our first case, map biopsies revealed Acanthamoeba cysts in 2 of the 4 biopsies. This led to an inferotemporally eccentric 8.5-mm PKP. The final histology report indicated that the closest resection margin was 0.08 mm. In our second case, the peripheral map biopsies were clear and an inferiorly eccentric 8.25-mm PKP was performed. The final histology report indicated that the closest resection margin was 2.3 mm. Both grafts have remained clear at 6 months postoperatively.

CONCLUSIONS

Map biopsies of the cornea can achieve total removal of the corneal tissues infested with Acanthamoeba cysts and prevent reinfection of the donor graft.

Microbiological Profile of Infectious Keratitis During Covid-19 Pandemic

Purpose

The Covid-19 pandemic introduced significant changes in our daily life, including the widespread use of face masks. The purpose of this study was to assess if significant changes occurred in the microbiological profile of infectious keratitis.

Patients and Methods

A retrospective study was performed, based on a survey review of the electronic medical records of all patients with presumed infectious keratitis, between March 2020 and October 2021. The microbiological isolates in this sample (pandemic group) were compared with those obtained in our center between 2009 and 2018 (pre-pandemic group).

Results

A total of 194 samples were included in the pandemic group. We obtained a culture-positivity rate of 43.3%, which was significantly higher when compared with the pre-pandemic data (35.15%, p = 0.033). Several further significant differences were found between the pandemic and the pre-pandemic groups: the proportion of bacteria, including gram-positive and gram-negative groups, was higher in our sample (pre-pandemic vs pandemic: 76.78% vs 83.33%, p = 0.010; 53.35% vs 60.71%, p = 0.016; 23.43% vs 34.52%, p = 0.005, respectively); two populations of Gram-positive bacteria found in this study were not isolated in the pre-pandemic sample - Dolosigranulum pigrum and Propionibacterium spp.; and two bacterial isolates were significantly increased in our sample - Corynebacterium spp. (18.41% vs 29.76%, p = 0.003) and Pseudomonas aeruginosa (9.00% vs 16.66%, p = 0.012).

Conclusion

In conclusion, significant changes were found in the microbiological profile of infectious keratitis in our center during the Covid-19 pandemic. While these changes could be related to face mask use, more observational and experimental studies are needed to explore this possible association.

Ocular streptococcal infections: A clinical and microbiological review

Streptococcus is a diverse bacterial genus that is part of the ocular surface microbiome implicated in conjunctivitis, keratitis, endophthalmitis, dacryocystitis, and orbital cellulitis which can lead to decreased visual acuity and require surgical intervention. The pathophysiology of S. pneumoniae is well established and the role of the polysaccharide capsule, pneumolysin, neuraminidases, and zinc metalloproteinases in ocular infections described. Additionally, key virulence factors of the viridans group streptococci such as cytolysins and proteases have been outlined, but there is a paucity of research on the remaining streptococcus species. These virulence factors tend to result in aggressive disease. Clinically, S. pneumoniae is implicated in 2.7-41.2% of bacterial conjunctivitis cases, more predominant in the pediatric population, and is implicated in 1.8-10.7% of bacterial keratitis isolates. Streptococcus bacteria are significantly implicated in acute postoperative, post-intravitreal, and bleb-associated endophthalmitis, responsible for 10.3-37.5, 29.4, and 57.1% of cases, respectively. Group A and B streptococcus endogenous endophthalmitis is rare, but has a very poor prognosis. Inappropriate prescription of antibiotics in cases of non-bacterial aetiology has contributed to increasing resistance, and a clinical index is needed to more accurately monitor this. Furthermore, there is an increasing need for prospective, surveillance studies of antimicrobial resistance in ocular pathogens, as well as point-of-care testing using molecular techniques.

Utility of investigation for suspected microbial keratitis: a diagnostic accuracy study

PURPOSE

The true disease status of a population with suspected microbial keratitis (MK) cannot be verified. There is not an accurate (gold) reference standard to confirm infection and inter-test comparisons of sensitivity and specificity therefore lead to bias with questionable estimates of test utility. We present an alternative method to report results.

METHODS

We used a decision to treat as the definition for MK. We retrospectively compared the results of corneal culture and polymerase chain reaction (PCR) as these are objective tests available for the three principal groups of pathogens. We then estimated the potential contribution of positive results, either alone or in combination, to support the working diagnosis.

RESULTS

We included 2021 (77.4%) eyes with suspected bacterial keratitis, 365 (14.0%) with suspected acanthamoeba keratitis, and 226 (8.6%) with suspected fungal keratitis, all treated between July 2013 and December 2019. In these groups, there were 51.6% positive culture and 6.5% positive PCR results for bacteria, 19.0% and 40.5% for acanthamoeba, and 28.3% and 15.0% for fungi. Between groups the differences in the proportions of positive results from culture and PCR was statistically significant (P < 0.001). The added benefit of PCR to the result of culture in identifying a potential pathogen was 1.4% for bacteria (P = 0.6292), 24.4% for acanthamoeba (P = 0.0001), and 5.8% for fungi (P = 0.3853).

CONCLUSIONS

For suspected MK a comparison of the test positivity rate is an easily comprehensible outcome measure of test utility.

Comparison of culture, confocal microscopy and PCR in routine hospital use for microbial keratitis diagnosis

AIMS

To evaluate the sensitivity and specificity of polymerase chain reaction (PCR), in vivo confocal microscopy (IVCM) and culture for microbial keratitis (MK) diagnosis.

METHODS

Retrospective review of PCR, IVCM and culture results for MK diagnosis at Moorfields Eye Hospital between August 2013 and December 2014.

RESULTS

PCR results were available for 259 MK patients with concurrent culture for 203/259 and IVCM for 149/259. Sensitivities and specificities with 95% confidence intervals [95% CI] were calculated for Acanthamoeba keratitis (AK) and fungal keratitis (FK), by comparison with culture, for both IVCM and PCR. For AK, FK and bacterial keratitis (BK) sensitivities were calculated, for each diagnostic method, by comparison with a composite reference standard (a positive result for one or more of culture, PCR or IVCM having a specificity of 100% by definition). For the latter, sensitivities with [95% CI] were: for AK, IVCM 77.1% [62.7-88.0%], PCR 63.3% [48.3-76.6%], culture 35.6 [21.9-51.2]; for FK, IVCM 81.8% [48.2-97.7%], PCR 30.8% [9.09-61.4%], culture 41.7% [15.2-72.3%]; for BK, PCR 25.0% [14.7-37.9%], culture 95.6% [87.6-99.1%].

CONCLUSION

IVCM was the most sensitive technique for AK and FK diagnosis but culture remains our gold standard for BK. These findings reflect results to be expected from service providers to UK ophthalmology units and demonstrates the need at our centre for ongoing diagnostic result audit leading to the potential to improve PCR diagnosis. Both FK and AK are now common in the UK; ophthalmology units need to have all these techniques available to optimise their MK management.

Infectious Keratitis Isolates and Susceptibility in Southern California

PURPOSE

The purpose of this study was to determine longitudinal trends in prevalence and resistance profiles for infectious keratitis at referral centers in Southern California.

METHODS

Cultured infectious keratitis cases from January 1, 2006, through December 31, 2009, and January 1, 2016, through December 31, 2019, at the University of California, Los Angeles, were evaluated. Outcome measures included microbial isolate prevalence and antibiotic/antifungal susceptibility and resistance patterns.

RESULTS

One hundred thirty-nine and 315 culture-positive isolates were obtained between 2006-2009 and 2016-2019, respectively. Gram-positive organisms accounted for 65% (2006-2009) and 74% (2016-2019) of bacterial isolates ( P = 0.076). Staphylococcus infections, the most common gram-positive and bacterial isolate in both study epochs, demonstrated increased prevalence from 2006-2009 to 2016-2019 (41% vs. 53%, P = 0.019). Although coagulase-negative Staphylococcus (CoNS) increased from 40% to 58% ( P = 0.0012), the prevalence of methicillin-resistant Staphylococcus aureus was unchanged (28% vs. 28%, P = 0.99). Pseudomonas aeruginosa , the most common gram-negative organism, demonstrated decreased prevalence from 18% to 10% ( P = 0.027). Candida species comprised 3.5% of culture-positive isolates in both epochs. All gram-positive isolates were susceptible to vancomycin, and all Staphylococcus isolates were susceptible to linezolid. Pseudomonas aeruginosa remained susceptible to tested fluoroquinolones (>93%) and aminoglycosides (100%) over time.

CONCLUSIONS

In southern California between 2006 and 2019, there was a shift toward Staphylococcus species, with increased CoNS, decreased methicillin-sensitive Staphylococcus aureus , and decreased prevalence of P. aeruginosa . Empiric therapy of vancomycin and a fluoroquinolone or aminoglycoside provides effective antibacterial coverage for predominant bacterial species when culture sensitivities are pending.

Trends in Infectious Keratitis in Taiwan: An Update on Predisposing Factors, Microbiological and Antibiotic Susceptibility Patterns

Infectious keratitis (IK) represents a major cause of corneal blindness. This study aims to investigate the demographics, risk factors, microbiological characteristics and antibiotic susceptibility patterns of IK in Taiwan over the past 15 years. A retrospective population-based study was conducted using the Chang Gung Research Database. Patients with IK were identified by diagnostic codes for corneal ulcer from 2004 to 2019. Of 7807 included subjects, 45.2% of patients had positive corneal cultures. The proportion of contact lens-related IK declined, while that of IK related to systemic diseases grew. The percentage of isolated gram-positive bacteria surpassed that of gram-negative bacteria in the 15-year period. The prevalence of Pseudomonas aeruginosa showed a decreasing trend (p = 0.004), whereas coagulase-negative Staphylococcus (CNS) and Propionibacterium species were increasingly detected (p < 0.001). Overall, the trend of antibiotic susceptibility of both gram-positive and gram-negative bacteria did not change throughout the study period. The susceptibility to the test antibiotics maintained over 90% in gram-negative isolates over 15 years. Vancomycin preserved 100% susceptibility to all gram-positive isolates. Since most tested antibiotics exhibited stable susceptibility over decades, this study reinforced that fluoroquinolones and fortified vancomycin continue to be good empiric therapies for treating bacterial keratitis in Taiwan.

Clinical and microbiological analysis of fungal keratitis in Toronto, Canada: A 20-year study

Fungal keratitis is a devastating and difficult-to-treat ocular infection with high morbidity. Understanding geographic microbiological and clinical trends helps to guide rapid and effective treatment. We therefore report the characteristics and outcomes of fungal keratitis in Toronto, Canada over a twenty-year period. An electronic search of microbiology records at University Health Network, Toronto, ON, Canada identified all patients with positive corneal fungal culture over a 20-year period seen at our tertiary referral cornea practice. Review of corresponding patient charts identified demographic and microbiological details, clinical course, treatment regimen, and final outcomes associated with each episode of culture-positive fungal keratitis. Forty-six patients with fifty-one discrete fungal keratitis episodes were included. Five patients experienced recurrent fungal keratitis. Candida species accounted for 60.8% of positive fungal cultures, followed by Filamentous species at 35.3%. Preferred initial anti-fungal treatment was topical amphotericin at 36.7% followed by topical voriconazole at 32.6%. Surgical intervention was required in 48.9% with therapeutic penetrating keratoplasty being the most common procedure (22.4%). Final visual acuity (VA) of < 20/200 was attributed to 58% of patients in this study. Risk factors for poor outcomes included poor VA, topical steroid use at presentation, Candida involvement, history of ocular surface disease, organic ocular trauma, or prior corneal transplantation. Candida is the most frequent keratomycotic pathogen in Toronto. Risk factors for poor visual outcome include prior corneal transplantation, ocular surface disease/trauma, or pre-existing topical steroid use. Early suspicion, diagnosis and treatment are paramount for best clinical outcomes.

Spectrum and resistance in bacterial infections of the ocular surface in a German tertiary referral center 2009-2019

Purpose

Aim of this study was to evaluate the frequencies, trends, and antibiotic resistance of bacteria collected from ocular surface or contact lens material in a German tertiary referral center from 2009 to 2019.

Methods

Microbiological data from 2009 to 2019 was analyzed. Culture-dependent microbial identification and analysis of antibiotic sensitivity was completed by the Institute of Microbiology. Statistical analysis of age- and sex-specific differences as well as changes in the microbial spectrum and resistance over the study period was performed with GraphPad Prism 9.0 applying nonparametric tests (level of significance: p ≦ 0.05).

Results

A total of 6361 specimens were analyzed. Positivity rate was 18.6%. Sixty-three percent (n = 680) of the bacterial isolates were derived from ocular surface and 37% (n = 399) from contact lens material. The ratio of gram-negative bacteria was significantly higher in contact lens material. Multiresistant bacteria showed a significant increase with patient age (p < 0.0001). An overall increase in resistance to levofloxacin (p = 0.0239) was detected. Only 2.4% and 3.1% isolates were resistant to a combination of moxifloxacin and gentamicin, respectively, levofloxacin and gentamicin.

Conclusions

The reported bacterial spectrum is similar to comparable centers. Our data show that it should not be assumed that the newest classes of antibiotics have the best efficacy or lowest resistance levels. In suspected bacterial conjunctivitis, we propose using gentamicin as first-line therapy. In therapy refractive cases and in involvement of the cornea, we recommend a combination of gentamicin and ofloxacin or moxifloxacin. Overall, the evaluated organisms showed good sensitivity to the regularly used antibiotics.

Outcomes of Microbial Keratitis Cases Resistant to Antimicrobials in Sydney, Australia

PURPOSE

The purpose of this study was to describe demographics, predisposing factors, clinical features, treatment, and outcomes of microbial keratitis cases resistant to antimicrobials.

METHODS

A retrospective case series was conducted. All patients with microbial keratitis resistant to antimicrobials who underwent a corneal scrape and culture from 2012 to December 2016 at the Sydney Eye Hospital were included. Cases were identified from pathology and hospital coding data. Coagulase-negative staphylococci (CoNS), Staphylococcus aureus (S. aureus), and Corynebacterium spp. resistant to cefalotin, chloramphenicol, ciprofloxacin, or gentamicin were analyzed.

RESULTS

One hundred fifteen episodes had a resistant CoNS, 24 S. aureus, and 12 Corynebacterium spp. Antimicrobial resistance was associated with older women (67%, median age 83 years) with Corynebacterium spp. (P < 0.001), corneal graft, and previous topical steroid use. Larger epithelial defects (P = 0.203) and infiltrates (P = 0.180) were more likely to be associated with Corynebacterium spp., but not statistically significant. At the initial and final visits, resistant S. aureus (75% vs. 67%) and Corynebacterium spp. (78% vs. 80%) cases were more likely to be classified as blind (>3/60) compared with CoNS (45% vs. 28%) (P = 0.011 vs. P = 0.004). Corneal perforation occurred more often in resistant S. aureus cases (P < 0.001), whereas slow and nonhealing epithelial defects needing other procedures were more likely to occur with resistant Corynebacterium spp. (P < 0.001).

CONCLUSIONS

Patients with resistant CoNS were younger and presented with smaller ulcers and moderate vision loss. Visual and clinical outcomes were significantly better for resistant CoNS than for those with resistant S. aureus or Corynebacterium spp.

Comparison of Culture-Positive and -Negative Microbial Keratitis

Objectives:

To evaluate and compare the risk factors, presenting features, and outcomes of patients with culture-positive and culturenegative microbial keratitis (MK) who presented to a tertiary referral center.

Materials and Methods:

We conducted a retrospective review of the medical records of 314 patients who were diagnosed with MK in our clinic between 2012 and 2019.

Results:

Among 314 patients, 142 had positive cultures (45.2%). The mean ages of the culture-positive and -negative patients at the time of diagnosis were 51.39±21.31 (range, 14-90) years and 56.68±21.34 (7-94) years, respectively (p=0.028). The mean best corrected visual acuity (BCVA) of the culture-positive and -negative patients were1.74±1.25 (0-3.1) LogMAR and 1.91±1.23 (0-3.1) LogMAR prior to treatment and increased to 1.21±1.30 (0-3.1) LogMAR and 1.27± 1.29 (0-3.1) LogMAR at last visit, respectively. There was no statistically significant difference between culture-positive and -negative patients’ BCVA levels at presentation or last visit. Ninety-two patients (64.7%) were infected with bacteria and 50 patients (35.2%) with fungi. The most common pathogen was Pseudomonas aeruginosa (18.3%), followed by Streptococcus pneumoniae (11.2%) and Fusarium spp. (11.2%). Keratitis foci were either centrally or paracentrally located in 105 eyes (73.9%) of culture-positive patients and 149 eyes (86.6%) of culture-negative patients. Multiple foci were present mostly in culture-positive patients (p=0.001). There was no significant difference between the culture-positive and -negative groups in terms of hypopyon presence (p=0.364). The proportion of contact lens (CL) wearers was 33% (n=47) among culturepositive MK patients and 13.3% (n=23) among culture-negative MK patients, respectively (p<0.001). Culture positivity was found to be significantly higher in keratitis associated with CL use (p=0.0001).

Conclusion:

Microbiological analysis and culture evaluation are important steps in order to manage proper treatment in microbial keratitis. Prognosis mostly depends on the infectivity of the microbiological agent.

Pathogens and Antibiotic Susceptibilities of Global Bacterial Keratitis: A Meta-Analysis

Bacterial keratitis (BK) is the most common type of infectious keratitis. The spectrum of pathogenic bacteria and their susceptibility to antibiotics varied with the different regions. A meta-analysis was conducted to review the global culture rate, distribution, current trends, and drug susceptibility of isolates from BK over the past 20 years (2000–2020). Four databases were searched, and published date was limited between 2000 and 2020. Main key words were “bacterial keratitis”, “culture results” and “drug resistance”. Forty-two studies from twenty-one countries (35 cities) were included for meta-analysis. The overall positive culture rate was 47% (95%CI, 42–52%). Gram-positive cocci were the major type of bacteria (62%), followed by Gram-negative bacilli (30%), Gram-positive bacilli (5%), and Gram-negative cocci (5%). Staphylococcus spp. (41.4%), Pseudomonas spp. (17.0%), Streptococcus spp. (13.1%), Corynebacterium spp. (6.6%) and Moraxella spp. (4.1%) were the most common bacterial organism. The antibiotic resistance pattern analysis revealed that most Gram-positive cocci were susceptive to aminoglycoside (86%), followed by fluoroquinolone (81%) and cephalosporin (79%). Gram-negative bacilli were most sensitive to cephalosporin (96%) and fluoroquinolones (96%), followed by aminoglycoside (92%). In Gram-positive cocci, the susceptibility trends of fluoroquinolones were decreasing since 2010. Clinics should pay attention to the changing trends of pathogen distribution and their drug resistance pattern and should diagnose and choose sensitive antibiotics based on local data.

Ocular surface flora and prophylactic antibiotics for cataract surgery in the age of antimicrobial resistance

According to the World Health Organization alert about the antimicrobial resistance crisis released in 2015, clinicians should strongly reconsider the prolonged use of antimicrobials. In this review, we focus on the ocular surface flora with respect to the trend of fluoroquinolone resistance, and its upset and restoration after topical administration of antimicrobials and preservatives. Even 3 weeks of topical administration of levofloxacin (LVFX) yields a selection of fluoroquinolone-resistant isolates bearing genetic changes in the ocular surface flora. One month of topical prophylactic administration of LVFX after cataract surgery induces the loss of diversity with LVFX-resistance of the ocular surface flora. Restoration of LVFX-sensitive flora occurs 6 to 9 months after the final topical administration of LVFX. The ocular surface flora recovers earlier in patients given LVFX for 1 week after the surgical procedure. These findings suggest that shorter periods of postoperative topical antibiotics are less frequently associated with persistent antimicrobial-resistant bacteria in the ocular flora. In addition, microbiologic analysis of ocular surfaces treated with a long period of eye drops containing benzalkonium chloride (BAC) showed a higher incidence of isolates resistant to methicillin and fluoroquinolones than did ocular surfaces treated with eye drops not containing BAC. To avoid the emergence of antimicrobial-resistant bacteria on the ocular surface, an urgent discussion must be held about the appropriate use of antibiotics and preservatives in the ophthalmology field.

Bacterial keratitis: identifying the areas of clinical uncertainty

Bacterial keratitis is a common corneal infection that is treated with topical antimicrobials. By the time of presentation there may already be severe visual loss from corneal ulceration and opacity, which may persist despite treatment. There are significant differences in the associated risk factors and the bacterial isolates between high income and low- or middle-income countries, so that general management guidelines may not be appropriate. Although the diagnosis of bacterial keratitis may seem intuitive there are multiple uncertainties about the criteria that are used, which impacts the interpretation of investigations and recruitment to clinical studies. Importantly, the concept that bacterial keratitis can only be confirmed by culture ignores the approximately 50% of cases clinically consistent with bacterial keratitis in which investigations are negative. The aetiology of these culture-negative cases is unknown. Currently, the estimation of bacterial susceptibility to antimicrobials is based on data from systemic administration and achievable serum or tissue concentrations, rather than relevant corneal concentrations and biological activity in the cornea. The provision to the clinician of minimum inhibitory concentrations of the antimicrobials for the isolated bacteria would be an important step forward. An increase in the prevalence of antimicrobial resistance is a concern, but the effect this has on disease outcomes is yet unclear. Virulence factors are not routinely assessed although they may affect the pathogenicity of bacteria within species and affect outcomes. New technologies have been developed to detect and kill bacteria, and their application to bacterial keratitis is discussed. In this review we present the multiple areas of clinical uncertainty that hamper research and the clinical management of bacterial keratitis, and we address some of the assumptions and dogma that have become established in the literature.

Comparative Genomic and Pan-Genomic Characterization of Staphylococcus epidermidis From Different Sources Unveils the Molecular Basis and Potential Biomarkers of Pathogenic Strains

Coagulase-negative Staphylococcus (CoNS) is the most common pathogen causing traumatic endophthalmitis. Among which, Staphylococcus epidermidis is the most common species that colonizes human skin, eye surfaces, and nasal cavity. It is also the main cause of nosocomial infection, specially foreign body-related bloodstream infections (FBR-BSIs). Although some studies have reported the genome characteristics of S. epidermidis, the genome of ocular trauma-sourced S. epidermidis strain and a comprehensive understanding of its pathogenicity are still lacking. Our study sequenced, analyzed, and reported the whole genomes of 11 ocular trauma-sourced samples of S. epidermidis that caused traumatic endophthalmitis. By integrating publicly available genomes, we obtained a total of 187 S. epidermidis samples from healthy and diseased eyes, skin, respiratory tract, and blood. Combined with pan-genome, phylogenetic, and comparative genomic analyses, our study showed that S. epidermidis, regardless of niche source, exhibits two founder lineages with different pathogenicity. Moreover, we identified several potential biomarkers associated with the virulence of S. epidermidis, including essD, uhpt, sdrF, sdrG, fbe, and icaABCDR. EssD and uhpt have high homology with esaD and hpt in Staphylococcus aureus, showing that the genomes of S. epidermidis and S. aureus may have communicated during evolution. SdrF, sdrG, fbe, and icaABCDR are related to biofilm formation. Compared to S. epidermidis from blood sources, ocular-sourced strains causing intraocular infection had no direct relationship with biofilm formation. In conclusion, this study provided additional data resources for studies on S. epidermidis and improved our understanding of the evolution and pathogenicity among strains of different sources.

Adjunctive Thymosin Beta-4 Treatment Influences MΦ Effector Cell Function to Improve Disease Outcome in Pseudomonas aeruginosa-Induced Keratitis

Our previous work has shown that topical thymosin beta 4 (Tβ4) as an adjunct to ciprofloxacin treatment reduces inflammatory mediators and inflammatory cell infiltrates (neutrophils/PMN and macrophages/MΦ) while enhancing bacterial killing and wound healing pathway activation in an experimental model of P. aeruginosa-induced keratitis. This study aimed to mechanistically examine how Tβ4 influences MΦ function in particular, leading to reduced inflammation and enhanced host defense following P. aeruginosa-induced infection of the cornea. Flow cytometry was conducted to profile the phenotype of infiltrating MΦ after infection, while generation of reactive nitrogen species and markers of efferocytosis were detected to assess functional activity. In vitro studies were performed utilizing RAW 264.7 cells to verify and extend the in vivo findings. Tβ4 treatment decreases MΦ infiltration and regulates the activation state in response to infected corneas. MΦ functional data demonstrated that the adjunctive Tβ4 treatment group significantly downregulated reactive nitrogen species (RNS) production and efferocytotic activity. In addition, the in vitro studies showed that both Tβ4 alone and adjunctive Tβ4 treatment influenced MΦ cellular function following LPS stimulation. Collectively, these data provide further evidence that adjunctive Tβ4 + ciprofloxacin treatment offers a more efficacious option for treating bacterial keratitis. Not only does the adjunctive therapy address both the infectious pathogen and corneal wound healing response, but it also influences MΦ infiltration, activation, and function, as revealed by the current study.

Infectious Keratitis After Boston Type 1 Keratoprosthesis Implantation

PURPOSE

To identify the incidence, risk factors, and outcomes of infectious keratitis after Boston type 1 keratoprosthesis (kpro) implantation.

METHODS

Retrospective case series of kpro procedures at the Stein Eye Institute and the Centre Hospitalier de l'Université de Montréal between May 1, 2004, and December 31, 2018. Data were collected regarding ocular history, operative details, postoperative management, microbiologic profile, treatment, and outcomes. Log-rank test and Cox proportional hazard ratio (HR) were used to evaluate for an association between risk factors and outcomes.

RESULTS

A total of 349 kpro procedures were performed in 295 eyes of 268 patients. Fifty-seven cases of presumed infectious keratitis were identified after 53 procedures (15.2%) in 50 eyes (16.9%) of 49 patients (18.3%). The incidences of culture-positive bacterial and fungal keratitis were 0.014 and 0.004 per eye-year, respectively. Persistent corneal epithelial defect formation (P < 0.001) and cicatricial disease (HR: 1.98, 95% confidence interval, 1.02-3.83) were associated with a significantly higher incidence of infectious keratitis. For the 53 cases with a known outcome, medical therapy achieved resolution of infection in 34 cases (64.2%), whereas kpro explantation was required in 19 cases (35.8%). Infectious keratitis was associated with an increased risk for kpro explantation (HR: 3.09, 95% confidence interval, 1.92-4.79).

CONCLUSIONS

Infectious keratitis develops in approximately 17% of eyes after kpro implantation, with a higher rate of culture-positive bacterial than fungal keratitis. The observed rate of microbial keratitis suggests the need for additional topical antimicrobial prophylaxis in eyes at higher risk, such as those with preexisting cicatricial disease or postoperative persistent corneal epithelial defect formation.

Microbial Spectrum and Resistance Patterns in Ocular Infections: A 15-Year Review in East China

Purpose

To report antibiotic resistance rates and trends of common ocular isolates collected over a 15-year period.

Methods

We collected 3533 isolates from July 1, 2005 to July 31, 2020. Antibiotic sensitivity was determined according to the guidelines of the Clinical and Laboratory Standards Institute. Chi-squared (χ²) test was used to analyze changes in antibiotic susceptibility over 15 years.

Results

Among the 3533 isolates, the predominant pathogens were the staphylococcal species. Methicillin resistance was observed in 381 Staphylococcus aureus (S. aureus) isolates (46.4%) and 1888 coagulase-negative staphylococci (CoNS) isolates (61.1%), and methicillin-resistant (MR) isolates had a high probability of concurrent resistance to fluoroquinolones and aminoglycosides. The mean percentage of resistance in staphylococcal isolates did not reach statistical significance across patient age groups (P = 0.87). Methicillin resistance did not increase in the CoNS (P = 0.546) isolates, and resistance to methicillin slightly decreased among S. aureus (P = 0.04) isolates over 15 years. Additional exploratory analysis revealed a small decrease in resistance to tobramycin (P = 0.01) and chloramphenicol (P < 0.001) among the CoNS isolates. All staphylococcal isolates were susceptible to vancomycin.

Conclusion

Staphylococci were the most common microorganisms responsible for causing ocular infections. Antibiotic resistance was high among staphylococci, with nearly half of these isolates were resistant to methicillin and these had a high probability of concurrent resistance among MR staphylococci to other antibiotics. Overall, ocular resistance did not significantly change during the 15-year study period. We conclude that continued surveillance of antibiotic resistance provides critical data to guide antibiotic selection.

Corneal Culture in Infectious Keratitis: Effect of the Inoculation Method and Media on the Corneal Culture Outcome

Background: To compare two different methods of corneal culture in infectious keratitis: multiple sampling for direct inoculation and enrichment (standard method) and a single sample via transport medium for indirect inoculation (indirect inoculation method). Methods: Prospective inclusion of patients fulfilling predefined criteria of infectious keratitis undergoing corneal culture according to both studied methods in a randomized order. Results: The standard method resulted in a significantly higher proportion of positive culture outcomes among the 94 included episodes of infectious keratitis (61%; 57/94) than the indirect inoculation method (44%; 41/94) (p = 0.002) and a significantly higher proportion of microorganisms than the indirect inoculation method, with a Cohen’s kappa of 0.38 (95% CI: 0.28–0.49) for agreement between the methods. Subanalysis of culture results showed that direct inoculation on gonococcal agar only combined with the indirect inoculation method resulted in a similar rate of culture positive patients and proportion of detected microorganisms to the standard method. Conclusion: Indirect inoculation of one corneal sample cannot replace direct inoculation of multiple corneal samples without loss of information. A combination of directly and indirectly inoculated samples can reduce the number of corneal samples by four without statistically significant differences in culture outcome or in the proportion of detected microorganisms.

Epithelium-Penetrable Nanoplatform with Enhanced Antibiotic Internalization for Management of Bacterial Keratitis

A standardized regimen for addressing the adverse effects of bacterial keratitis on vision remains an intractable challenge due to poor epithelial penetration and a short corneal retention time. In this study, a new strategy is proposed to implement the direct transport of antibiotics to bacteria-infected corneas via topical administration of an epithelium-penetrable biodriven nanoplatform, thereby enabling the efficacious treatment of bacterial keratitis. The nanoplatforms were composed of amphiphilic glycopolymers containing boron dipyrromethene and boronic acid moieties with stable fluorescence characteristics and the ability to potentiate epithelial penetration deep into the cornea. The boronic acid-derived nanoplatforms enabled efficient cellular internalization through the high affinity of boric acid groups for the diol-containing bacterial cell wall, resulting in enhanced drug penetration and retention inside the pathogenic bacteria. The bacterial cells formed agglomerations after incorporating the nanoplatforms along with a special mechanism to release the encapsulated cargo in response to in situ bacteria. Compared with the drug alone, this smart system achieved enhanced bacterial mortality and attenuated inflammation associated with Staphylococcus aureus-induced keratitis in rats, demonstrating a paradigm for targeted ocular drug delivery and an alternative strategy for managing bacterial keratitis or other bacterial infections by heightening corneal permeability and transcorneal bioavailability.

Evaluation of full-length nanopore 16S sequencing for detection of pathogens in microbial keratitis

BACKGROUND

Microbial keratitis is a leading cause of preventable blindness worldwide. Conventional sampling and culture techniques are time-consuming, with over 40% of cases being culture-negative. Nanopore sequencing technology is portable and capable of generating long sequencing reads in real-time. The aim of this study is to evaluate the potential of nanopore sequencing directly from clinical samples for the diagnosis of bacterial microbial keratitis.

METHODS

Using full-length 16S rRNA amplicon sequences from a defined mock microbial community, we evaluated and benchmarked our bioinformatics analysis pipeline for taxonomic assignment on three different 16S rRNA databases (NCBI 16S RefSeq, RDP and SILVA) with clustering at 97%, 99% and 100% similarities. Next, we optimised the sample collection using an ex vivo porcine model of microbial keratitis to compare DNA recovery rates of 12 different collection methods: 21-gauge needle, PTFE membrane (4 mm and 6 mm), Isohelix™ SK-2S, Sugi® Eyespear, Cotton, Rayon, Dryswab™, Hydraflock®, Albumin-coated, Purflock®, Purfoam and Polyester swabs. As a proof-of-concept study, we then used the sampling technique that provided the highest DNA recovery, along with the optimised bioinformatics pipeline, to prospectively collected samples from patients with suspected microbial keratitis. The resulting nanopore sequencing results were then compared to standard microbiology culture methods.

RESULTS

We found that applying alignment filtering to nanopore sequencing reads and aligning to the NCBI 16S RefSeq database at 100% similarity provided the most accurate bacterial taxa assignment. DNA concentration recovery rates differed significantly between the collection methods (p < 0.001), with the Sugi® Eyespear swab providing the highest mean rank of DNA concentration. Then, applying the optimised collection method and bioinformatics pipeline directly to samples from two patients with suspected microbial keratitis, sequencing results from Patient A were in agreement with culture results, whilst Patient B, with negative culture results and previous antibiotic use, showed agreement between nanopore and Illumina Miseq sequencing results.

CONCLUSION

We have optimised collection methods and demonstrated a novel workflow for identification of bacterial microbial keratitis using full-length 16S nanopore sequencing.

Microbes of the human eye: Microbiome, antimicrobial resistance and biofilm formation

BACKGROUND

The review focuses on the bacteria associated with the human eye using the dual approach of detecting cultivable bacteria and the total microbiome using next generation sequencing. The purpose of this review was to highlight the connection between antimicrobial resistance and biofilm formation in ocular bacteria.

METHODS

Pubmed was used as the source to catalogue culturable bacteria and ocular microbiomes associated with the normal eyes and those with ocular diseases, to ascertain the emergence of anti-microbial resistance with special reference to biofilm formation.

RESULTS

This review highlights the genetic strategies used by microorganisms to evade the lethal effects of anti-microbial agents by tracing the connections between candidate genes and biofilm formation.

CONCLUSION

The eye has its own microbiome which needs to be extensively studied under different physiological conditions; data on eye microbiomes of people from different ethnicities, geographical regions etc. are also needed to understand how these microbiomes affect ocular health.

Morphological and cytokine profiles as key parameters to distinguish between Gram-negative and Gram-positive bacterial keratitis

Bacterial keratitis (BK) is an ocular disorder associated with poor visual prognosis. Quantification of the associated inflammatory response may provide insight into the pathogenesis of BK and guide treatment options. In this exploratory study, we evaluated 45 BK patients and 20 healthy controls by optical coherence tomography and pro-inflammatory tear cytokine analysis. The aim was to quantify the differential morphological and cytokine inflammatory response between Gram-negative and Gram-positive BK and to determine the diagnostic value of corneal thickness (CT) and infiltrate thickness (IT) in distinguishing Gram-ve BK in a clinical cohort. Greater CT and IT, at clinical presentation, were indicative of Gram-ve infection with values detected of ≥ 950 μm and ≥ 450 μm, respectively. Combination of these CT and IT values had a 100% sensitivity and 83.3% specificity as a diagnostic indicator of Gram-ve infection. Similarly, there were higher levels of IL-1β, IL-6 and IL-8 cytokines were quantified in keratitis caused by Gram-negative bacteria. Among the different tear cytokines analysed, a significant reduction after three days of treatment was detected for pro-inflammatory cytokines IL-1β, IL-2, IL-6, IL-8 and TNF-α, prior to starting with the administration of steroid drops. Overall, this study shows the potential value of serial OCT and tear cytokine measurements in the management of BK.

Silencing TLR4/MyD88/NF-κB Signaling Pathway Alleviated Inflammation of Corneal Epithelial Cells Infected by ISE

The regulatory role of toll-like receptor 4 (TLR4) in the inactivate staphylococcus epidermidis (ISE)-induced cornea inflammation is not well investigated. Here, TLR4 silence could decrease inflammatory cytokines in corneal epithelial cells treated with ISE. The mouse corneal epithelial cells were exposed to ISE for 24 h, either alone or with the NF-κB inhibitor, TLR4 lentivirus to bilaterally (knock-down or and overexpression). The expression of TLR4 in mouse corneal epithelial cells was investigated using western blot and qRT-PCR assay. The inflammatory cytokine levels were evaluated by qRT-PCR and ELISA, respectively. The relative impact factors of TLR4-mediated NF-κB signaling detected using western blot assay. Results show the expression levels of TLR4 and some inflammatory cytokines were significantly increased in corneal epithelial cells treated with ISE. TLR4 Silence markedly decreased ISE-induced production of IL12, TNF-α, CCL5, and CCL9 in corneal epithelial cells. Furthermore, the nuclear translocation of NF-κB p65 and myeloid differentiation protein 88 (MyD88) in the cells treated with ISE were further reduced by silencing TLR4. Inhibition of TLR4-mediated NF-κB signaling by using BAY11-7082 also alleviated ISE-induced inflammation. In the rescue experiment, transfected the stable TLR4 silenced corneal epithelial cells with TLR4 overexpression lentivirus, we found that TLR4 overexpression can restore the down-regulation of TLR4 and inflammatory cytokines (IL12, TNF-α, CCL9) caused by TLR4 knocked down. Therefore, ISE-induced cornea inflammation was due to the activation of the TLR4/MyD88/NF-κB signaling pathway, and dramatically stimulated IL12, TNF-α, CCL9 secretion. TLR4 silence presented mitigates damage in corneal epithelial cells treated with ISE.

A Rare Case of Mixed Infectious Keratitis Caused by <b><i>Pseudomonas koreensis</i></b> and <b><i>Aspergillus fumigatus</i></b>

We report the clinical and microbiological features of contact lens-related mixed infectious keratitis caused by a spore-forming filamentous fungus and a rare gram-negative bacterial infection. A 66-year-old Caucasian female presented with right eye (OD) pain after sleeping in her 2-weekly contact lenses for 3 days. On presentation, corrected distance visual acuity was 0.46 LogMAR OD and 0.20 in the left eye. Slit lamp biomicroscopy revealed a 1.9 mm by 1.9 mm area of dense stromal infiltrate with epithelial defect. Corneal scrapes grew Aspergillus fumigatus and Pseudomonas koreensis, and culture-directed microbial therapy with oral and topical voriconazole and topical fortified gentamicin along with regular debridement resulted in slow resolution of the infection, leaving a dense stromal scar in the visual axis requiring penetrating keratoplasty. Mixed infectious keratitis caused by filamentous fungi and gram-negative bacteria is rare. Pseudomonas koreensis infection has not been previously reported as a cause of infectious keratitis in humans. In our experience, these mixed infections require prolonged systemic and topical therapy and the secondary scarring may require surgical intervention for vision rehabilitation.

Carbon Dots Fabrication: Ocular Imaging and Therapeutic Potential

Vision loss is a major complication in common ocular infections and diseases such as bacterial keratitis, age-related macular degeneration (AMD) and diabetic retinopathy (DR). The prevalence of such ophthalmic diseases represents an urgent need to develop safe, effective, and long-term treatments. Current therapies are riddled with drawbacks and limitations which calls for the exploration of alternative drug delivery mechanisms. Toxicity of the inorganic metals and metal oxides used for drug delivery raise safety concerns that are alleviated with the alternate use of, a natural and organic polymer which is both biocompatible and environmentally friendly. Carbon dots (CDs) represent a great potential in novel biomedical applications due to their tunable fluorescence, biocompatibility, and ability to be conjugated with diverse therapeutic materials. There is a growing interest on the exploitation of these properties for drug delivery with enhanced bio-imaging. However, there are limited reports of CD applications for ophthalmic indications. In this review, we focus on the CD potential and the development of translational therapies for ophthalmic diseases. The current review presents better understanding of fabrication of CDs and how it may be useful in delivering anti-bacterial agents, anti-VEGF molecules as well as imaging for ophthalmic applications.

Nucleic acid peptide nanogels for the treatment of bacterial keratitis

Cage-shaped nucleic acid nanocarriers are promising molecular scaffolds for the organization of polypeptides. However, there is an unmet need for facile loading strategies that truly emulate nature's host-guest systems to drive encapsulation of antimicrobial peptides (AMPs) without loss of biological activity. Herein, we develop DNA nanogels with rapid in situ loading of L12 peptide during the thermal annealing process. By leveraging the binding affinity of L12 to the polyanionic core, we successfully confine the AMPs within the DNA nanogel. We report that the thermostability of L12 in parallel with the high encapsulation efficiency, low toxicity and sustained drug release of the pre-loaded L12 nanogels can be translated into significant antimicrobial activity. Using an S. aureus model of infectious bacterial keratitis, we observe fast resolution of clinical symptoms and significant reduction of bacterial bioburden. Collectively, this study paves the way for the development of DNA nanocarriers for caging AMPs with immense significance to address the rise of resistance.

Spectrum of Microbial Keratitis Encountered in the Tropics

PURPOSE

To report the predisposing factors, microorganisms, antibiotic sensitivity associated with bacterial keratitis, and treatment outcomes in Miri, Borneo which has a tropical climate.

METHODS

This is a retrospective study on patients presenting with microbial keratitis in Miri, Sarawak, Borneo over a 7-year period from January 1, 2010 until December 31, 2016. Demographic data, predisposing factors, culture and sensitivity results together with treatment outcomes were studied.

RESULTS

There were a total of 221 cases treated as microbial keratitis with a peak age group of 21 to 30 years. The predisposing factors were trauma (49.3%), improper contact lens usage (29.1%), ocular surface diseases (5.9%), ocular surgeries (0.9%), drugs (1.8%), and other factors (19.0%). Occupational injuries among oil palm plantation workers was the leading cause within the trauma cohort (28.8%). Corneal scraping was performed in 189 cases, 61.4% of them yielded positive cultures. The cultures demonstrated that 49.1% were of bacterial origin, 46.6% were fungal, and 4.3% showed mixed growth. The most common bacteria isolated was Pseudomonas aeruginosa, which was sensitive toward ceftazidime and gentamicin antibiotics. One hundred ninety-two cases (86.9%) were treated with purely topical medication, whereas 29 cases (13.1%) required further interventions.

CONCLUSION

The commonest predisposing factor for microbial keratitis was trauma. With the nearby oil palm industries, we report a corresponding increase of incidence in fungal keratitis at our center. Culture and sensitivity reports from corneal scrapings are essential in treatment guidance; however, more than a third of the microbial keratitis cases studied were culture-negative. The organisms cultured reflect the profile expected in tropical climates. Fortunately, there was no increase in resistance rates observed for the commonly used antibiotics.

Antimicrobial susceptibility of isolated pathogens from patients with contact lens-related bacterial keratitis in Crete, Greece: A ten-year analysis

PURPOSE

To evaluate the bacterial spectrum and antimicrobial susceptibilities of pathogens isolated from contact lens-related bacterial keratitis cases in a large academic Greek hospital.

METHODS

All adult patients with positive corneal scrapings or contact lens culture between 2007 and 2016 at the University Hospital of Heraklion, Greece, were retrospectively identified through a local microbiology database and their medical records were reviewed.

RESULTS

A total of 240 isolates were recovered from 131 patients with culture-proven contact lens-associated bacterial keratitis. The most common microorganism identified was Serratia marcescens (17.1% of total isolates), followed by Pseudomonas aeruginosa, Klebsiella spp. and coagulase-negative staphylococci (CoNS). Rates of aztreonam-resistant P. aeruginosa and erythromycin-resistant CoNS decreased in recent years, while the decrease in oxacillin-resistant CoNS was statistically significant (p=0.009). More than 90% of the isolated organisms (S. marcescens, P. aeruginosa, Klebsiella spp. and CoNS) were susceptible to ciprofloxacin or gentamicin.

CONCLUSION

Gram-negative microorganisms are the most common causative pathogens of contact lens-related keratitis in the region of Crete. Topical antibacterials containing quinolones or gentamicin represent an effective empirical treatment for the majority of the cases. This is quite encouraging, considering that the present study was conducted in a country characterised by high antimicrobial resistance rates. However, culture-driven antimicrobial treatment is mandatory for this sight-threatening infection.

Infectious keratitis: isolated microbes and their antibiotic susceptibility pattern during 2004-2014 in Region Örebro County, Sweden

PURPOSE

To describe predisposing risk factors, causative microorganisms and their antibiotic susceptibility patterns in infectious keratitis during an 11-year period in Region Örebro County, Sweden.

METHODS

This is a descriptive study conducted as a retrospective audit of clinical records. Patients who received treatment for infectious keratitis at any of the three ophthalmological departments within Region Örebro County, Sweden, between 2004 and 2014 were included if they fulfilled the predefined criteria for infectious keratitis. Data regarding culture results, antibiotic susceptibility pattern and risk factors for infectious keratitis were obtained from medical records and microbiological reports.

RESULTS

In total, 398 episodes of infectious keratitis in 392 patients were included, and 285 were culture positive. The most common predisposing risk factor was contact lens wear (45%). Coagulase-negative staphylococci (39.6%) was the most commonly isolated type of organism. Staphylococcus aureus (15.1%) followed by Moraxella spp. (7.4%) and Pseudomonas aeruginosa (6.7%) were among the most common isolated bacteria not considered to be commensal. Reduced susceptibility to fluoroquinolones was observed in five of 43 S. aureus isolates and in four of nine Streptococcus pneumoniae isolates.

CONCLUSION

The most common predisposing risk factor for keratitis was contact lens wear. Among the most common microbes, not considered to be exclusively commensals, isolated from the cornea in microbial keratitis were S. aureus, Moraxella spp. and P. aeruginosa. The antibiotic susceptibility patterns showed low proportion of resistance. Empiric treatment of suspected infectious keratitis with topical fluoroquinolones and chloramphenicol might be considered in a setting like ours pending culture results.

Etiology and Risk Factors for Infectious Keratitis in South Texas

Purpose

To determine the causative organisms and associated risk factors for infectious keratitis in South Texas.

Methods

This retrospective study was performed at a tertiary teaching hospital system in South Texas. Medical records of all patients who presented with infectious keratitis from 2012 to 2018 were reviewed. Only patients with culture-proven bacterial, fungal, and Acanthamoeba keratitis were included.

Results

In total, 182 eyes of 181 patients had culture-proven bacterial, fungal, or Acanthamoeba keratitis. The age of patients ranged from 3 to 93 years, with a mean of 48.3 ± 20.8 years. The most common etiologic agent was bacteria, with 173 bacterial cultures (95.1%) recovered, followed by 13 fungal cultures (7.1%), and 3 Acanthamoeba cultures (1.6%). Of the 218 bacterial isolates, coagulase-negative Staphylococcus was the most common (25.7%), followed by Pseudomonas aeruginosa (23.4%), Staphylococcus aureus (11.0%), and Moraxella (7.8%). Fusarium was the most common fungal isolate (46.2%). The most common risk factors for infectious keratitis included contact lens wear (32.4%), underlying corneal disease (17.6%), trauma (14.3%), and ocular surface disease (13.7%).

Conclusions

Bacteria are the most common cause of infectious keratitis in this patient population, with coagulase-negative Staphylococcus and Pseudomonas as the most common isolates. The prevalence of culture-positive fungal keratitis is significantly lower than that of bacterial keratitis. Contact lens wear is the most common risk factor associated with infectious keratitis in South Texas.

Antimicrobial resistance trends in bacterial keratitis over 5 years in Sydney, Australia

IMPORTANCE

Antimicrobial resistance (AMR) patterns in bacterial keratitis may fluctuate in a geographic location over time.

BACKGROUND

To investigate any change in AMR patterns in Sydney, Australia.

DESIGN

Retrospective case series.

PARTICIPANTS

All patients with microbial keratitis who underwent a corneal scrape and culture from 2012 to 2016 at the Sydney Eye Hospital.

METHODS

Matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry identified organisms. The Calibrated Dichotomous Susceptibility method determined antibiotic susceptibilities.

MAIN OUTCOME MEASURES

Isolated organisms and antibiotic susceptibilities.

RESULTS

There were 1084 corneal scrapes from 957 patients. The mean age was 54 years (range 18-100) and 52% were male. Cultures were positive in 711 of 1084 scrapes (66%), with 884 organisms identified. Of the bacteria isolated, 685 of 884 (78%) were Gram-positive and 199 of 884 (22%) were Gram-negative. Overall, the most common bacteria were coagulase-negative Staphylococci (CoNS) (405/884, 46%). Methicillin-resistance was detected in 7% of Staphylococcus aureus isolates (7/103). Methicillin-resistance in CoNS (ie, also cefalotin resistance) was reported in 19% of isolates and ciprofloxacin 8%. For methicillin-sensitive S aureus (MSSA), 5% of isolates were resistant to ciprofloxacin. For Corynebacterium spp., 34% of isolates were resistant to chloramphenicol and 9% to ciprofloxacin. The most common Gram-negative bacteria was Pseudomonas aeruginosa (109/199, 55%). One case was resistant to ciprofloxacin.

CONCLUSIONS AND RELEVANCE

Coagulase-negative staphylococcal species were the most frequently suspected of causing bacterial keratitis. Increased resistance to cefalotin was identified for CoNS and to ciprofloxacin for Corynebacterium spp., MSSA and P aeruginosa compared to a previous study in Sydney in 2002 to 2003.

Microbiological Profile of Infectious Keratitis in a Portuguese Tertiary Centre

The microbiological profile of infectious keratitis has shown great differences across the world. Due to the continuous shifting trends in microbiological profile and antibiotic resistance patterns reported in several studies, constant local updates are crucial to provide an adequate treatment. The propose of this study was to analyze the incidence of infectious keratitis, possible changing trends in microbiological profile, and bacteria sensitivity to commonly used antibiotics, in our tertiary center, in the last 10 years. A retrospective study was performed, based on the survey review of electronic medical records of all patients with presumed infectious keratitis, between January 1, 2009, and December 31, 2018. Microbial cultures were performed, and patients were treated according to an internal protocol. A total of 1360 samples were included. We obtained a 35.1% culture-positive rate. Bacteria accounted for 76.78% of all positive scrapes (53.34% were Gram positive and 23.44% were Gram negative), Acanthamoeba for 12.13%, fungi for 8.16%, and virus for 2.93%. The most frequent agent identified was Corynebacterium macginleyi (18.41%), followed by Staphylococcus aureus (17.78%), Streptococcus pneumoniae (9.41%), and Pseudomonas aeruginosa (9.00%). We identified at least one ophthalmologic risk factor in 410 patients (85.77%). Trauma and contact lens wear were the most common risk factors found, accounting for 34.94% (n = 167) and 33.47% (n = 160) of cases. Sensitivity to fluoroquinolones and aminoglycosides was tested in all bacterial isolates, presenting values of 96.66% and 98.12%. In our region, the most common bacteria are Staphylococcus aureus, Streptococcus pneumoniae, and Pseudomonas aeruginosa, and they showed high sensitivity rates to first-line antibiotics, without any modification or emergence of antibiotic resistance trends during the 10 years of the study. For this reason, we decided to maintain the same internal protocol in our tertiary centre.

Microbial Keratitis in Taiwan: A 20-Year Update

PURPOSE

To investigate the demographics, risk factors, microbiology, and resistance pattern at a tertiary hospital and to detect the shifting trend over 2 decades.

DESIGN

A retrospective observational case series.

METHODS

We reviewed all records of patients with microbial keratitis (MK) that were hospitalized in National Taiwan University Hospital between 2007 and 2016. Demographics, predisposing factors, pathogens, and clinical courses were compared to our previous study conducted from 1992 to 2001. Antibiotic susceptibility was compared with those conducted from 1994 to 2005.

RESULTS

The percentage of patients 60 years and older in the MK population was increasing (P = 2.1E-21). The proportion of trauma-related MK declined while MK related to chronic ocular or systemic disorders rose. The prevalence of nontuberculous mycobacteria (NTM) showed a decreasing trend (P = .0032), whereas Microsporidia has been increasingly detected. The 2 most common bacterial isolates were Pseudomonas aeruginosa (35.2%) and Staphylococcus species (13.2%). Management of these infection did not differ in common pathogens between the 2 decades. The susceptibility of Staphylococcus species to oxacillin reduced significantly (P = .002) and there was an increase in methicillin-resistant Staphylococcus aureus keratitis.

CONCLUSIONS

Contact lens wear remained the most common predisposing factor, with Pseudomonas species as the major pathogen. However, chronic disorder-related MK was on the rise along with an increasing trend of oxacillin resistance in Staphylococcus species. We found a decreasing trend in NTM keratitis while Microsporidia keratitis was considered as an emerging ocular disease. Though gram-negative isolates remained susceptible to all antibiotics tested, antibiotic resistance was more common in gram-positive isolates.

Nine-year analysis of isolated pathogens and antibiotic susceptibilities of microbial keratitis from a large referral eye center in southern China

Purpose: To analyze the genus profile of isolated pathogens and antibiotic susceptibility trends of microbial keratitis over nine years at a large referral eye center in southern China.

Methods: Data of corneal specimens from January 2010 to August 2018 of patients clinically diagnosed with infectious keratitis were obtained from the center’s microbiology database. Results with positive cultures along with antibiotic susceptibility were reviewed and analyzed.

Results: We collected and reviewed 7,229 specimens, including 3,092 with positive cultures. Among them, 1,630 (52.72%) were bacterial, 1781 (57.60%) were fungal, and 319 (10.32%) were coinfected. A significant decreasing trend was observed in the isolates of Gram-positive cocci (r =−0.711, P=0.032), among which the proportion of coagulase-negative staphylococcus (CNS) was also reduced (r =−0.883, P=0.002). In contrast, an increasing trend in the proportion of Gram-negative bacilli was observed (r=0.661, P=0.053). The susceptibility rates of Gram-positive cocci to cephalosporins were near 90%, which was relatively high compared to fluoroquinolones. Fluoroquinolones represented the antibiotics to which Gram-negative bacilli were the most susceptible. Their susceptibility to moxifloxacin was 78.79%. The overall performance of aminoglycosides and vancomycin was both around 70%. The susceptibility of Gram-positive cocci to several antibiotics including levofloxacin (r=−0.717, P=0.03), tobramycin (r= −0.933, P<0.001), cefazolin (r= −0.964, P<0.001), ceftazidime (r=−0.929, P=0.003), chloramphenicol (r=−0.929, P=0.003), and cefuroxime (r=−0.829, P=0.042) decreased over time. The susceptibility of Gram-negative bacilli to ofloxacin increased over time (r=0.854, P=0.004), whereas that to cefazolin (r=−0.833, P=0.005) and chloramphenicol (r=−0.886, P=0.019) decreased over time.

Conclusion: From 2010 to 2018 in Zhongshan Ophthalmic Center, most isolates from infectious keratitis were Gram-positive cocci (mainly CNS), which decreased over time, with an increase in Gram-positive bacilli. More than half of the antibiotics showed reducing trend of susceptibilities, and the antibiotic resistance situation in southern China was not encouraging.