Comparison of the ocular microbiome between chronic Stevens-Johnson syndrome patients and healthy subjects

Impact of streptozotocin-induced type 1 and type 2 diabetes on ocular surface microbial signatures in C57BL/6J mice

The ocular surface (OS), like other mucosal sites, hosts a diverse microbiome. However, the impact of hyperglycemia associated with diabetes on OS microbial composition remains poorly understood. In this study, we established type 1 diabetes mellitus (T1DM) and type 2 diabetes mellitus (T2DM) models in C57BL/6J mice by administering high-dose streptozotocin (STZ) for T1DM and low-dose STZ combined with a high-fat diet for T2DM. The OS microbiome was characterized and analyzed using 16S rRNA sequencing. The results showed that neither T1DM nor T2DM significantly affected microbial richness compared to normal mice; however, T2DM led to a significant reduction in microbial diversity. This reduction in microbial diversity in T2DM is consistent with known microbial dysbiosis in diabetes, which may contribute to the pathogenesis of ocular complications such as dry eye disease and diabetic retinopathy. Community composition analysis identified Proteobacteria, Pelagibacterium, and Aliihoeflea as the core OS bacteria in normal mice. Diabetes significantly altered the OS microbial composition at various taxonomic levels. Specifically, T1DM was associated with 9 signature bacterial species, including Oceanospirillales, Bacillales, Halomonas, unclassified_f_Lachnospiraceae, and Anoxybacillus. T2DM exhibited 17 bacterial markers, including Firmicutes, Staphylococcus, Corynebacterium, and Parasutterella. Functional prediction of the microbiota using PICRUSt2 indicated potential impairments in carbohydrate metabolism due to diabetes. In conclusion, diabetic mice exhibit severe dysregulation of their OS microbiota, and restoring microbial balance in diabetic patients may represent a promising strategy for preventing and treating diabetic OS pathologies.

Diagnosing and Managing Stevens-Johnson Syndrome and Toxic Epidermal Necrolysis in Adults: Review of Evidence 2017-2023

Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) are life-threatening reactions associated with long-term disabling sequelae. In the acute phase, the best supportive care in expert centers is the cornerstone of treatment. The follow-up is prolonged and multidisciplinary, according to the patient's needs. In this paper, we review the evidence from 2017 to 2023 for the diagnosis and management of SJS/TEN in adults. On the basis of this review and our own experience, we present recommendations for the diagnosis of SJS/TEN in adults, management in the acute phase (best supportive care; prevention of infections; skin, ocular, and other mucosa management; intensive care measures; and etiological treatment), and follow-up. The most frequent sequelae are cutaneous, ocular, and psychological. High-quality studies assessing the efficacy of immunomodulating agents (eg, cyclosporine, corticosteroids, intravenous Igs, and anti-TNF agents) in accelerating healing and reducing mortality are still lacking. In addition, we propose avenues for future studies.

Ocular involvement in Steven-Johnson syndrome/toxic epidermal necrolysis: recent insights into pathophysiology, biomarkers, and therapeutic strategies

PURPOSE OF REVIEW

To review the pathophysiology, recent biomarkers related to the ocular aspects of Steven-Johnson syndrome (SJS)/toxic epidermal necrolysis (TEN), and to highlight notable evidence published in recent years.

RECENT FINDINGS

Several studies reveal the relationship between tear cytokines and the pathological components in eyes of SJS/TEN patients. Specific clinical features and associated risk factors in the acute stage have shown significant correlations with chronic ocular sequelae. Recent treatment protocols, including early pulse systemic and topical steroids, as well as tumor necrosis factor-α inhibitors, have demonstrated positive effects on ocular outcomes. In addition to conventional surgical treatment, a new surgical technique, simple oral mucosal epithelial transplantation (SOMET), has been introduced as a simple ocular surface reconstruction for patient with SJS.

SUMMARY

Advancements in knowledge and management strategies have notably enhanced ocular outcomes for SJS/TEN eyes. A deeper understanding of the biomarker changes in these eyes could facilitate the development of future targeted treatment options.

Changes in the ocular surface microbiome of patients with coronavirus disease 2019 (COVID-19)

Purpose

To elucidate the reasons behind the increased incidence of ocular disease in patients with coronavirus disease 2019 (COVID-19), this study delved deeper into the specific effects of COVID-19 on patients' ocular surface microbiome (OSM) and investigated its relationship with the increased incidence of ocular disease.

Methods

In this study, conjunctival sac swabs were collected from 43 participants for 16S rRNA amplicon sequencing. The participants were categorized into three groups based on their COVID-19 status: the control group (C group) consisted of 15 participants who showed no evidence of COVID-19, the experimental group (E group) included 15 participants who tested positive for COVID-19, and the COVID-19 recovery period group (R group) comprised 13 participants.

Results

In the comparison of alpha diversity, group E had a higher Shannon, Chao1 and Goods coverage index. When comparing beta diversity, groups E and R were more similar to each other. At the phylum level, although the OSM of the three groups was dominated by Proteobacteria, Actinobacteriota, Bacteroidota and Firmicutes, the compositional proportions were significantly different. At the genus level, the dominant species in the three OSM groups were significantly different, with Pseudomonas becoming the dominant genus in groups E and R compared to group C, and the abundance of Ralstonia decreasing significantly.

Conclusion

This study provides additional evidence supporting the association between the OSM and COVID-19, which contributes to our understanding of the potential mechanisms underlying ocular symptoms and complications associated with COVID-19 in the future.

Exploring the Ocular Surface Microbiome and Tear Proteome in Glaucoma

Although glaucoma is a leading cause of irreversible blindness worldwide, its pathogenesis is incompletely understood, and intraocular pressure (IOP) is the only modifiable risk factor to target the disease. Several associations between the gut microbiome and glaucoma, including the IOP, have been suggested. There is growing evidence that interactions between microbes on the ocular surface, termed the ocular surface microbiome (OSM), and tear proteins, collectively called the tear proteome, may also play a role in ocular diseases such as glaucoma. This study aimed to find characteristic features of the OSM and tear proteins in patients with glaucoma. The whole-metagenome shotgun sequencing of 32 conjunctival swabs identified Actinobacteria, Firmicutes, and Proteobacteria as the dominant phyla in the cohort. The species Corynebacterium mastitidis was only found in healthy controls, and their conjunctival microbiomes may be enriched in genes of the phospholipase pathway compared to glaucoma patients. Despite these minor differences in the OSM, patients showed an enrichment of many tear proteins associated with the immune system compared to controls. In contrast to the OSM, this emphasizes the role of the proteome, with a potential involvement of immunological processes in glaucoma. These findings may contribute to the design of new therapeutic approaches targeting glaucoma and other associated diseases.

Lid Margin Microbiome in Stevens-Johnson Syndrome Patients With Lid Margin Keratinization and Severe Dry Eye Disease

Purpose

The current study evaluated the lid margin microbiome of keratinized lid margins of patients with chronic Stevens-Johnson syndrome (SJS) and compared it with healthy controls and historically reported lid margin microbiome of patients with meibomian gland dysfunction (MGD).

Methods

Eyelid margin swabs of 20 asymptomatic adults (mean age = 29 ± 12 years) and 10 patients with chronic SJS (mean age = 31.2 ± 14 years) with lid margin keratinization were sequenced using next generation of 16S rDNA V3 to V4 variable region. Within SJS, the keratinized lid margin microbiome was compared with adjacent eyelid skin.

Results

All patients had obstructive MGD, and mean Schirmer I value was 2.8 ± 1.9 mm. The phyla were similar in two groups, whereas at the genera level, an increase in the relative abundance of Corynebacterium, Haemophilus, Azotobacter, and Afipia and a decrease of Acinetobacter was noted in SJS compared to healthy lid margins. SJS-associated microbiota displayed lesser diversity and more heterogeneity than healthy controls. The Principal Components Analysis (PCA) plot revealed wide separation in the SJS and the control groups. Correlational network analysis revealed Corynebacterium and Sphingomonas forming a major hub of negative interactions with other bacterial genera in the SJS group. Significant differences exist in the prevalent genera between keratinized lid margins and historically reported meibum microbiome of patients with MGD. In addition, the eyelid skin of patients with SJS had predominant Staphylococcus, whereas Corynebacterium and Pseudomonas were more in the keratinized lid margins compared to the eyelid skin microbiome.

Conclusions

Lid margin microbiome is significantly altered in the keratinized lid margins of patients with SJS compared to the eyelid skin of patients with SJS, normal lid margins, and patients with MGD.

The Conjunctival Microbiome and Dry Eye: What We Know and Controversies

ABSTRACT

Dry eye disease is a common multifactorial condition that may be idiopathic or associated with autoimmune conditions, such as Sjogren syndrome. Commensal microorganisms modify immune responses, so it is relevant to understand how they modify such immune-mediated diseases. Microbiota in the gut regulate inflammation in the eye, and conversely, severe inflammation of the ocular surface results in alteration of gut microbiome. The conjunctiva microbiome can be analyzed using 16S or shotgun metagenomics. The amount of microbial DNA in ocular surface mucosa relative to human DNA is limited compared with the case of the intestinal microbiome. There are challenges in defining, harvesting, processing, and analyzing the microbiome in the ocular surface mucosa. Recent studies have shown that the conjunctiva microbiome depends on age, presence of local and systemic inflammation, and environmental factors. Microbiome-based therapy, such as the use of oral probiotics to manage dry eye disease, has initial promising results. Further longitudinal studies are required to investigate the alteration of the conjunctival microbiome after local therapy and surgery.

Unique composition of ocular surface microbiome in the old patients with dry eye and diabetes mellitus in a community from Shanghai, China

BACKGROUND

This study investigates the variations in microbiome abundance and diversity on the ocular surfaces of diabetic patients suffering from dry eye within a community setting. The goal is to offer theoretical insights for the community-level prevention and treatment of dry eye in diabetic cohorts.

METHODS

Dry eye screening was performed in the Shanghai Cohort Study of Diabetic Eye Disease (SCODE) from July 15, 2021, to August 15, 2021, in the Xingjing community; this study included both a population with diabetes and a normal population. The population with diabetes included a dry eye group (DM-DE, n = 40) and a non-dry eye group (DM-NoDE, n = 39). The normal population included a dry eye group (NoDM-DE, n = 40) and a control group (control, n = 39). High-throughput sequencing of the 16 S rRNA V3-V4 region was performed on conjunctival swab from both eyes of each subject, and the composition of microbiome on the ocular surface of each group was analyzed.

RESULTS

Significant statistical differences were observed in both α and β diversity of the ocular surface microbiome among the diabetic dry eye, diabetic non-dry eye, non-diabetic dry eye, and normal control groups (P < 0.05).

CONCLUSIONS

The study revealed distinct microecological compositions on the ocular surfaces between the diabetic dry eye group and other studied groups. Firmicutes and Anoxybacillus were unique bacterial phyla and genera in the dry eye with DM group, while Actinobacteria and Corynebacterium were unique bacterial phyla and genera in the normal control group.

[Methods for assessing the microbiological diversity of the ocular surface]

This review compares data from scientific studies on the microbial community of the ocular surface (OS) in conditionally healthy individuals using cultural methods (including culture-dependent diagnostic tests), microscopic and molecular genetic methods, and assesses the influence of research methods and sample preparation on the results. Concordance and discordance of the sets of identified microorganisms were analyzed using overlapping and non-overlapping methods of studying the microbial community of a healthy OS. The article presents tables showing the names of microorganisms that were identified in different sources. Cross-verification in taxa of different ranks helped confirm the following most frequently found microorganisms on healthy OS: coccomorphic microorganisms of the genera Staphylococcus, Micrococcus, Kocuria, Streptococcus, Enterococcus; gram-positive spore-forming bacilli of the genera Bacillus and Paenibacillus; gram-positive non-spore-forming rod-shaped bacteria, including Corynebacterium, but excluding Propionibacterium and Microbacterium; gram-negative non-spore-forming rod-shaped microorganisms of the genera Moraxella and Serratia. The study also assessed the effect of wearing soft contact lenses on the composition of the microbial community of the OS.

The Microbiome, Ocular Surface, and Corneal Disorders

The ocular surface microbiome is an emerging field of study that seeks to understand how the community of microorganisms found on the ocular surface may help maintain homeostasis or can potentially lead to disease and dysbiosis. Initial questions include whether the organisms detected on the ocular surface inhabit that ecological niche and, if so, whether there exists a core microbiome found in most or all healthy eyes. Many questions have emerged around whether novel organisms and/or a redistribution of organisms play a role in disease pathogenesis, response to therapies, or convalescence. Although there is much enthusiasm about this topic, the ocular surface microbiome is a new field with many technical challenges. These challenges are discussed in this review as well as a need for standardization to adequately compare studies and advance the field. In addition, this review summarizes the current research on the microbiome of various ocular surface diseases and how these findings may impact treatments and clinical decision-making.

Ocular surface microbiota dysbiosis contributes to the high prevalence of dry eye disease in diabetic patients

People with diabetes mellitus (DM) are at an increased risk for developing dry eye disease (DED). However, the mechanisms underlying this phenomenon remain unclear. Recent studies have found that the ocular surface microbiota (OSM) differs significantly between patients with DED and healthy people, suggesting that OSM dysbiosis may contribute to the pathogenesis of DED. This hypothesis provides a new possible explanation for why diabetic patients have a higher prevalence of DED than healthy people. The high-glucose environment and the subsequent pathological changes on the ocular surface can cause OSM dysbiosis. The unbalanced microbiota then promotes ocular surface inflammation and alters tear composition, which disturbs the homeostasis of the ocular surface. This "high glucose-OSM dysbiosis" pathway in the pathogenesis of DED with DM (DM-DED) is discussed in this review.

Metagenomic analysis of microbiological changes on the ocular surface of diabetic children and adolescents with a dry eye

BACKGROUND

Microbiome changes on the ocular surface may cause dry eyes. A metagenome assay was used to compare the microbiome composition and function of the ocular surface between diabetic children and adolescents with dry eye, diabetic children and adolescents without dry eye, and normal children.

MATERIALS AND METHODS

Twenty children and adolescents aged 8 to 16 with diabetes were selected from the Shanghai Children and Adolescent Diabetes Eye Study. Ten healthy children and adolescents belonging to the same age group were selected from the outpatient clinic during the same period. The participants were classified into the dry eye group (DM-DE group, n = 10), the non-dry eye group (DM-NDE group, n = 10) and the normal group (NDM group, n = 10). A conjunctival sac swab was collected for metagenomic sequencing, and the relationship between the microbiome composition and functional gene differences on the ocular surface with dry eye was studied.

RESULTS

The classification composition and metabolic function of the microorganisms on the ocular surface of children in the 3 groups were analyzed. It was found that children's ocular microbiota was composed of bacteria, viruses and fungi. There were significant differences in α diversity and β diversity of microbial composition of ocular surface between DM-DE group and NDM group(P<0.05). There were significant differences in α and β diversity of metabolic pathways between the two groups(P<0.05). The functional pathways of ocular surface microorganisms in diabetic children with dry eyes were mainly derived from human disease, antibiotic resistance genes, carbohydrate, coenzyme and lipid transport and metabolism-related functional genes; In normal children, the functional pathways were mainly derived from replication, recombination, repair, signal transduction and defense-related functional genes.

CONCLUSION

The DM-DE group have unique microbial composition and functional metabolic pathways. The dominant species and unique metabolic pathways of the ocular surface in the DM-DE group may be involved in the pathogenesis of dry eye in diabetic children.

Role of the ocular surface microbiome in allergic eye diseases

PURPOSE OF REVIEW

The purpose of this review is to provide an update on emerging literature on the role of the ocular surface microbiome (OSM) in allergic eye diseases.

RECENT FINDINGS

Findings in the literature suggest that the ocular surface microbiome plays a role in the pathophysiology and course of allergic disease of the ocular surface.

SUMMARY

Knowledge regarding the role of the ocular surface microbiome in allergic disease is important to guide development of targets for future therapeutic interventions.

Impact of Exposomes on Ocular Surface Diseases

Ocular surface diseases (OSDs) are significant causes of ocular morbidity, and are often associated with chronic inflammation, redness, irritation, discomfort, and pain. In severe OSDs, loss of vision can result from ocular surface failure, characterised by limbal stem cell deficiencies, corneal vascularisation, corneal opacification, and surface keratinisation. External and internal exposomes are measures of environmental factors that individuals are exposed to, and have been increasingly studied for their impact on ocular surface diseases. External exposomes consist of external environmental factors such as dust, pollution, and stress; internal exposomes consist of the surface microbiome, gut microflora, and oxidative stress. Concerning internal exposomes, alterations in the commensal ocular surface microbiome of patients with OSDs are increasingly reported due to advancements in metagenomics using next-generation sequencing. Changes in the microbiome may be a consequence of the underlying disease processes or may have a role in the pathogenesis of OSDs. Understanding the changes in the ocular surface microbiome and the impact of various other exposomes may also help to establish the causative factors underlying ocular surface inflammation and scarring, the hallmarks of OSDs. This review provides a summary of the current evidence on exposomes in various OSDs.

Ophthalmic Aspects of Stevens-Johnson Syndrome and Toxic Epidermal Necrolysis: A Narrative Review

The aim of our review article was to summarize the current literature on Stevens-Johnson syndrome (SJS) and its severe form, toxic epidermal necrolysis (TEN). SJS/TEN is a serious, rare multi-system, immune-mediated, mucocutaneous disease with a significant mortality rate that can lead to severe ocular surface sequelae and even to bilateral blindness. Restoration of the ocular surface in acute and chronic SJS/TEN is challenging. There are only limited local or systemic treatment options for SJS/TEN. Early diagnosis, timely amniotic membrane transplantation and aggressive topical management in acute SJS/TEN are necessary to prevent long-term, chronic ocular complications. Although the primary aim of acute care is to save the life of the patient, ophthalmologists should regularly examine patients already in the acute phase, which should also be followed by systematic ophthalmic examination in the chronic phase. Herein, we summarize actual knowledge on the epidemiology, aetiology, pathology, clinical appearance and treatment of SJS/TEN.

Ocular sequelae of epidermal necrolysis: French national audit of practices, literature review and proposed management

Stevens-Johnson Syndrome (SJS) and toxic epidermal necrolysis (TEN) are serious and rare diseases, most often drug-induced, and their incidence has been estimated at 6 cases/million/year in France. SJS and TEN belong to the same spectrum of disease known as epidermal necrolysis (EN). They are characterized by more or less extensive epidermal detachment, associated with mucous membrane involvement, and may be complicated during the acute phase by fatal multiorgan failure. SJS and TEN can lead to severe ophthalmologic sequelae. There are no recommendations for ocular management during the chronic phase. We conducted a national audit of current practice in the 11 sites of the French reference center for toxic bullous dermatoses and a review of the literature to establish therapeutic consensus guidelines. Ophthalmologists and dermatologists from the French reference center for epidermal necrolysis were asked to complete a questionnaire on management practices in the chronic phase of SJS/TEN. The survey focused on the presence of a referent ophthalmologist at the center, the use of local treatments (artificial tears, corticosteroid eye drops, antibiotic-corticosteroids, antiseptics, vitamin A ointment (VA), cyclosporine, tacrolimus), the management of trichiatic eyelashes, meibomian dysfunction, symblepharons, and corneal neovascularization, as well as the contactologic solutions implemented. Eleven ophthalmologists and 9 dermatologists from 9 of the 11 centers responded to the questionnaire. Based on questionnaire results, 10/11 ophthalmologists systematically prescribed preservative-free artificial tears, and 11/11 administered VA. Antiseptic or antibiotic eye drops or antibiotic-corticosteroid eye drops were recommended as needed by 8/11 and 7/11 ophthalmologists, respectively. In case of chronic inflammation, topical cyclosporine was consistently proposed by 11/11 ophthalmologists. The removal of trichiatic eyelashes was mainly performed by 10/11 ophthalmologists. Patients were referred to a reference center for fitting of scleral lenses (10/10,100%). Based on this practice audit and literature review, we propose an evaluation form to facilitate ophthalmic data collection in the chronic phase of EN and we also propose an algorithm for the ophthalmologic management of ocular sequelae.

Corneal bacterial microbiome in patients with keratoconus using next-generation sequencing-based 16S rRNA gene analysis

PURPOSE

To investigate the corneal bacterial microbiome in patients with keratoconus using next-generation sequencing and develop a new perspective on the pathogenesis of the disease.

METHODS

This prospective observational study included 10 patients with keratoconus who underwent corneal crosslinking procedure and 10 healthy controls who underwent photorefractive keratectomy. Patients included in the study were aged 18 years or older. The demographic and clinical characteristics of participants were recorded. Corneal epithelial samples were collected between March 2021 and June 2021. Isolated bacterial DNA from corneal epithelial samples was analyzed using 16 S ribosomal RNA gene analysis. The relative abundance rates at the phylum and genus levels were calculated. Alpha diversity parameters were assessed.

RESULTS

Eleven phyla and 521 genera of bacteria were identified in all participants. At the phylum level, Proteobacteria, Firmicutes, Actinobacteria, and Bacteroidetes were most abundant in both groups. There were no statistical differences between the two groups except Bacteriodetes (p < 0.05). At the genus level, the relative abundance rates of twenty bacteria were significantly different between keratoconus and healthy corneas (p < 0.05). Aquabacterium was the most abundant genus in patients with keratoconus, while Shigella was the most abundant genus in healthy controls. Alpha diversity parameters were lower in patients with keratoconus, although the difference did not reach statistical significance (p > 0.05).

CONCLUSIONS

Our preliminary study revealed that there are similarities and differences in the corneal microbiome between keratoconus and healthy individuals. Further research is required on the relationship between the abnormal corneal microbiome composition and the pathogenesis of keratoconus.

Microbiological Characteristics of Ocular Surface Associated With Dry Eye in Children and Adolescents With Diabetes Mellitus

Purpose

To analyze the characteristics of ocular surface microbial composition in children and adolescents with diabetes mellitus and dry eye (DE) by tear analysis.

Methods

We selected 65 children and adolescents aged 8 to 16 years with DE and non-DE diabetes mellitus and 33 healthy children in the same age group from the Shanghai Children and Adolescent Diabetes Eye Study. Tears were collected for high-throughput sequencing of the V3 and V4 region of 16S rRNA. The ocular surface microbiota in diabetic DE (DM-DE; n = 31), diabetic with non-DE (DM-NDE; n = 34), and healthy (NDM; n = 33) groups were studied. QIIME2 software was used to analyze the microbiota of each group.

Results

The DM-DE group had the highest amplicon sequence variants, and the differences in α-diversity and β-diversity of micro-organisms in the ocular surfaces of DM-DE, diabetic with non-DE, and healthy eyes were statistically significant (P < 0.05). Bacteroidetes (15.6%), Tenericutes (9.3%), Firmicutes (21.8%), and Lactococcus (7.9%), Bacteroides (7.8%), Acinetobacter (3.9%), Clostridium (0.8%), Lactobacillus (0.8%) and Streptococcus (0.2%) were the specific phyla and genera, respectively, in the DM-DE group.

Conclusions

Compared with the patients with non-DE and healthy children, the microbial diversity of the ocular surface in children and adolescents with diabetes mellitus and DE was higher with unique bacterial phyla and genera composition.

Shotgun metagenomic sequencing analysis of ocular surface microbiome in Singapore residents with mild dry eye

The ocular surface microbiome has implications for ocular surface inflammation and immunology. Previous shotgun metagenomics analyses were performed in China, showing results that differed according to environment and age. Patients with Sjogren's syndrome were reported to have altered conjunctival microbiome, but such studies have not been done in milder dry eye. The aim of this study is to describe the conjunctival microbiome in people with mild dry eye in Singapore. Samples were collected from 14 participants with mild dry eye and 10 age-matched comparison participants recruited from Singapore National Eye Centre (SNEC) clinics. Shotgun metagenomic sequencing analysis was employed to evaluate the conjunctival microbiome composition. Proteobacteria formed the predominant phylum in the conjunctiva. As in a study from a coastal city in China, Achromobacter spp. was numerically most abundant. Compared to age-matched controls, the conjunctival microbial composition in mild dry eye was similar. Several microorganisms, including Streptococcus spp. increased in representation with age, and the abundance of Staphylococcus correlated with Schirmer readings. In addition, when cultured corneal epithelial cells were exposed to three strains of Achromobacter xylosoxidans, cytokines such as TNF-α and IL-6 were upregulated in the cell lysates and supernatants. Ourresults suggest that age is an important factor that affects composition of the conjunctival microbiome, and relative abundance of specific microorganism may vary according to the environment of the human host.

Exploring the Healthy Eye Microbiota Niche in a Multicenter Study

Purpose: This study aims to explore and characterize healthy eye microbiota. Methods: Healthy subjects older than 18 years were selected for this descriptive cross-sectional study. Samples were collected with an eSwab with 1 mL of Liquid Amies Medium (Copan Brescia, Italy). Following DNA extraction, libraries preparation, and amplification, PCR products were purified and end-repaired for barcode ligation. Libraries were pooled to a final concentration of 26 pM. Template preparation was performed with Ion Chef according to Ion 510, Ion 520, and Ion 530 Kit-Chef protocol. Sequencing of the amplicon libraries was carried out on a 520 or 530 chip using the Ion Torrent S5 system (Thermo Fisher; Waltham, MA, USA). Raw reads were analyzed with GAIA (v 2.02). Results: Healthy eye microbiota is a low-diversity microbiome. The vast majority of the 137 analyzed samples were highly enriched with Staphylococcus, whereas only in a few of them, other genera such as Bacillus, Pseudomonas, and Corynebacterium predominate. We found an average of 88 genera with an average Shannon index of 0.65. Conclusion: We identified nine different ECSTs. A better understanding of healthy eye microbiota has the potential to improve disease diagnosis and personalized regimens to promote health.

Characterization and Comparison of Ocular Surface Microbiome in Newborns

The ocular microbiome is of fundamental importance for immune eye homeostasis, and its alteration would lead to an impairment of ocular functionality. Little evidence is reported on the composition of the ocular microbiota of term infants and on the impact of antibiotic prophylaxis. Methods: A total of 20 conjunctival swabs were collected from newborns at birth and after antibiotic treatment. Samples were subjected to 16S rRNA sequencing via system MiSeq Illumina. The data were processed with the MicrobAT software and statistical analysis were performed using two-way ANOVA. Results: Antibiotic prophylaxis with gentamicin altered the composition of the microbiota. In detail, a 1.5- and 2.01-fold reduction was recorded for Cutibacterium acnes (C. acnes) and Massilia timonae (M. timonae), respectively, whereas an increase in Staphylococcus spp. of 6.5 times occurred after antibiotic exposure. Conclusions: Antibiotic prophylaxis altered the ocular microbiota whose understanding could avoid adverse effects on eye health.

Mycobiomes of the Ocular Surface in Bacterial Keratitis Patients

Inflammation of the cornea is known as keratitis, and bacteria, fungi, protozoans, and viruses are the etiological agents of this disease. Delayed treatment of keratitis could result in loss of vision and, under certain severity conditions, the removal of an eye and its associated structures. In the current study, the ocular surface (conjunctiva and cornea) mycobiomes of individuals with bacterial keratitis were compared with the ocular mycobiome (conjunctiva) of healthy individuals, free of any ocular morbidity. Mycobiomes were generated through NGS approach using conjunctival swabs and corneal scrapings as the source of DNA from which ITS2 was amplified and sequenced, as a proxy to identify fungi. The results indicated significant changes in the alpha-diversity indices and in the abundance at the phylum and genera level. Hierarchical clustering using a heatmap showed that the mycobiomes were different. Furthermore, NMDS plots also differentiated the mycobiomes in the three cohorts, implying dysbiosis in the mycobiomes of the conjunctivae and corneal scrapings of bacterial keratitis individuals compared to control individuals. A preponderance of negative interactions in the hub genera in the conjunctival swabs of bacterial keratitis individuals compared to healthy controls further re-emphasized the differences in the mycobiomes. The dysbiotic changes at the genera level in conjunctivae and corneal scrapings of bacterial keratitis individuals are discussed with respect to their possible role in causing or exacerbating ocular surface inflammation. These results demonstrate dysbiosis in the ocular mycobiome in bacterial keratitis patients compared to healthy controls for the first time.

Epithelial barrier dysfunction in ocular allergy

The epithelial barrier is the first line of defense that forms a protective barrier against pathogens, pollutants, and allergens. Epithelial barrier dysfunction has been recently implicated in the development of allergic diseases such as asthma, atopic dermatitis, food allergy, and rhinitis. However, there is limited knowledge on epithelial barrier dysfunction in ocular allergy (OA). Since the ocular surface is directly exposed to the environment, it is important to understand the role of ocular epithelia and their dysfunction in OA. Impaired epithelial barrier enhances allergen uptake, which lead to activation of immune responses and development of chronic inflammation as seen in allergies. Abnormal expression of tight junction proteins that helps to maintain epithelial integrity has been reported in OA but sufficient data not available in chronic atopic (AKC) and vernal keratoconjunctivitis (VKC), the pathophysiology of which is not just complex, but also the current treatments are not completely effective. This review provides an overview of studies, which indicates the role of barrier dysfunction in OA, and highlights how ocular barrier dysfunction possibly contributes to the disease pathogenesis. The review also explores the potential of ocular epithelial barrier repair strategies as preventive and therapeutic approach.

Matrix metalloproteinase 9 is associated with conjunctival microbiota culture positivity in Korean patients with chronic Stevens-Johnson syndrome

Background

Stevens-Johnson syndrome (SJS) is an abnormal immune-response causing extensive exfoliation of the mucocutaneous tissue including conjunctiva. While several factors are associated with the alteration of conjunctival microbiota, the conjunctiva of SJS patients are found to harbor a different microbiota compared to healthy subjects. We investigated the conjunctival microbiota of Korean SJS patients, and identified factors associated with the conjunctival microbiota and its positive culture.

Methods

Medical records were retrospectively reviewed in 30 chronic SJS patients who had undergone conjunctival swab culture sampling. Demographic factors, chronic ocular surface complications score (COCS), tear break-up time (TBUT), tear secretion, tear matrix metalloproteinase 9 (MMP9), and results of conjunctival swab culture were assessed.

Results

Positive culture was seen in 58.1%. Gram positive bacteria was most commonly isolated, among which Coagulase-negative Staphylococci (45.5%) and Corynebacterium species (40.9%) were predominantly observed. Tear MMP9 positivity was observed significantly more in the positive culture group (100%) compared to the negative culture group (70%) (P = 0.041). Topical cyclosporine and corticosteroid were not associated with repetitive positive cultures. No significant differences in COCS, TBUT, and tear secretion were found between culture-positive and culture-negative groups.

Conclusion

Our study suggests that tear MMP9 positivity may be related with the presence of an abnormal ocular surface microbiota in chronic SJS patients.

Characterization of Conjunctival Sac Microbiome from Patients with Allergic Conjunctivitis

Conjunctival sac microbiome alterations have been reported to be closely associated with many ocular diseases. However, the characteristic of conjunctival sac microbiome in allergic conjunctivitis (AC) was scarcely described. In this study, we aimed to identify the differences of the conjunctival sac microbiome composition in AC patients compared with normal controls (NCs) using high-throughput 16S rDNA sequencing metagenomic analysis. The conjunctival sac microbiome samples from 28 AC patients and 39 NC patients were collected. The V3-V4 region of 16S rRNA gene high-throughput sequencing was performed on the illumina MiSeq platform. Alpha diversity, beta diversity and the relative abundance at the phylum and genus levels were analyzed using QIIME. Alpha diversity demonstrated by Chao1, Observed_species and PD_whole_tree indexes did not show significant difference between the AC and NC groups, while the Shannon index was higher in the AC group. Beta diversity showed divergent microbiome composition in different groups (p < 0.005). The top five abundant phyla were Firmicutes, Proteobacteria, Actinobacteriota, Bacteroidota and Cyanobacteria in both groups. The top five abundant genera were Bacillus, Staphylococcus, Corynebacterium, Acinetobacter and Ralstonia in the AC group and Acinetobacter, Staphylococcus, Bacillus, Clostridium_sensu_stricto_1, Corynebacterium and Geobacillus in the NC group. The Firmicutes/Bacteroidetes (F/B) ratio at the phylum level was similar between groups (p = 0.144). The Bacillus/Acinetobacter (B/A) ratio at the genus level was higher in the AC group (p = 0.021). The dysbiosis detected in this study might provide further evidence to investigate the mechanism and treatment methods for allergic conjunctivitis.

Fungi of the human eye: Culture to mycobiome

The focus of the current review is multi-fold and compares the diversity and abundance of fungi on the ocular surface by the conventional culture-based method with the more sensitive, high throughput, culture-independent NGS method. The aim is to highlight the existence of a core ocular mycobiome and explore the transition of the ocular fungal microbiota from the normal eye to the diseased eye. PubMed, Google Scholar and Medline were used to search for publications and reviews related to cultivable fungi and the mycobiome of the normal and diseased eye. The conventional cultivable approach and the NGS approach confirm that the eye has its own mycobiome and several confounding factors (age, gender, ethnicity etc.) influence the mycobiome. Further, dysbiosis in the mycobiome appears to be associated with ocular diseases and thus impacts the health of the human eye. Considering that the mycobiome of the eye is influenced by several confounding factors and also varies with respect to the disease status of the eye there is a need to extensively explore the mycobiome under different physiological conditions, different ethnicities, geographical regions etc. Such studies would unravel the diversity and abundance of the mycobiomes and contribute to our understanding of ocular health. Research focused on ocular mycobiomes may eventually help to build a targeted and individualized treatment.

Comparison of the Ocular Microbiomes of Dry Eye Patients With and Without Autoimmune Disease

Purpose

The pathogenesis of dry eye concomitant with autoimmune disease is different from that of dry eye without autoimmune disease. The aim of this study was to explore differences in the microbiota diversity and composition in dry eye with and without autoimmune disease.

Methods

Swab samples from the inferior fornix of the conjunctival sac were obtained from dry eye patients without autoimmune disease (n = 49, dry eye group) and from those with autoimmune disease (n = 38, immdry eye group). Isolated bacterial DNAs from swabs were analyzed with 16S rRNA amplicon sequencing.

Results

Analysis of the alpha diversity revealed no significant differences between subjects in the dry eye and immdry eye groups. Those in the immdry eye group had a distinct microbial composition compared with those in the dry eye group. The combination of the genera Corynebacterium and Pelomonas distinguished subjects in the immdry eye group from those in the dry eye group, with an area under the curve of 0.73 (95% CI = 0.62-0.84). For the same bacteria, the correlations between microbe abundance and the ocular surface parameters were different in the two groups. In addition, the functions of the microbial communities were altered in the two groups.

Conclusions

Our study demonstrates changes in the composition and function of the ocular microbiome between subjects in the immdry eye and dry eye groups, which suggests that the potential pathogenesis is different.

The Ocular Microbiome Is Altered by Sampling Modality and Age

Background

Studies of the ocular microbiome have used a variety of sampling techniques, but no study has directly compared different sampling methods applied to the same eyes to one another or to a reference standard of corneal epithelial biopsy. We addressed this lack by comparing the microbiome from three conjunctival swabs with those of corneal epithelial biopsy.

Methods

Twelve eyes (11 patients) were swabbed by calcium alginate swab, cotton-tipped applicator, and Weck-Cel cellulose sponge before a corneal epithelial biopsy (48 samples). We then performed 16S rRNA gene sequencing and universal 16S rRNA gene real-time polymerase chain reaction. Negative/blank controls were used to eliminate contaminants. An analysis was performed to examine the concordance of the three swab types to corneal epithelial biopsy. The effect of patient age on the ocular microbiome as determined by epithelial biopsy was also examined.

Results

The ocular microbiome from corneal epithelial biopsies consisted of 31 genera with a relative abundance of 1% or more, including Weisella, Corynebacterium, and Pseudomonas. Of the three swab types, Weck-Cel differed the most from corneal biopsies based on beta-diversity analysis. Cotton swabs were unable to capture the Bacteroides population seen on epithelial biopsy. Therefore, calcium alginate swabs seemed to be the closest to epithelial biopsies. Older patients (≥65 years old) had higher alpha diversity (P < 0.05) than younger patients. Differential abundance testing showed that there were 18 genera that were differentially abundant between the two age groups, including Streptococcus and eight members of the Proteobacteria phylum.

Conclusions

We demonstrate that ocular sampling method and patient age can greatly affect the outcome of sequencing-based analysis of the ocular microbiome.

Translational Relevance

By understanding the impact of different sampling methods on the results obtained from the ocular surface microbiome, future research on the topic will be more reproducible, leading to a better understanding of ocular surface microbiome in health and disease.

Comparison of structural components and functional mechanisms within the skin vs. the conjunctival surface

PURPOSE OF REVIEW

The purpose of this review is to highlight and compare the structural and functional differences between the ocular surface and the skin. The goal is to further understand how these components interact from an immunobiological standpoint, which may inform future therapeutic uses.

RECENT FINDINGS

Treatment agents, such as Dupilumab and Apremilast are traditionally indicated for integumentary conditions, such as atopic dermatitis and psoriasis, respectively. Both were also found to have potent effects on the conjunctival surface and ocular glands, which may be attributed to the similarities in structure.

SUMMARY

Surfaces of the eyes and the skin are found to have similar composition in terms of immunohistology, steroidogenic properties, and allergic mechanisms. These translate directly into both the adverse effects and therapeutic benefits that overlap when treating these surfaces.

Ocular Surface Microbiota in Diabetic Patients With Dry Eye Disease

Purpose

To investigate the ocular surface (OS) commensal bacteria profiles of patients with diabetes mellitus (DM) and dry eye disease (DED).

Methods

In the present study, subjects were assigned to four groups: 37 to the diabetic mellitus with dry eye disease (DM with DED) group, 22 to the diabetes mellitus (DM)-only group, 34 to the dry eye disease (DED)-only group, and 22 to the control group. Tear fluid was collected using Schirmer's tear secretion test paper. 16S ribosomal ribonucleic acid (rRNA) gene sequencing was used to analyze the bacterial microbiota.

Results

The DM with DED group showed the highest operational taxonomic unit (OTU) numbers and alpha diversity and the most different beta diversity. The groups shared the four most abundant phyla, accounting for over 96% of the total abundance. At the genus level, there were 10 types of overlap in the core microbiota in the groups. They showed significant differences between the groups. Additionally, the DM with DED group and the control group showed four unique core genera, respectively. Unclassified Clostridiales and Lactobacillus were the core microbiota members of the DM with DED group, the DM-only group, and the DED-only group, but not the control group.

Conclusions

In the present study, our results showed that the patients in the DM with DED group had a more complex and comprehensive ocular surface microbial composition. To the best of our knowledge, this is the first study to reveal the microbial profile of dry eye disease in patients with diabetes mellitus.

Acute and Chronic Management of Ocular Disease in Stevens Johnson Syndrome/Toxic Epidermal Necrolysis in the USA

Stevens Johnson syndrome and toxic epidermal necrolysis are on a spectrum of a severe, immune-mediated, mucocutaneous disease. Ocular involvement occurs in the vast majority of cases and severe involvement can lead to corneal blindness. Treatment in the acute phase is imperative in mitigating the severity of chronic disease. Advances in acute treatment such as amniotic membrane transplantation have shown to significantly reduce the severity of chronic disease. However, AMT is not a panacea and severe chronic ocular disease can and does still occur even with aggressive acute treatment. Management of chronic disease is equally critical as timely intervention can prevent worsening of disease and preserve vision. This mini-review describes the acute and chronic findings in SJS/TEN and discusses medical and surgical management strategies.

Clinical Aspects of Stevens-Johnson Syndrome and Toxic Epidermal Necrolysis With Severe Ocular Complications in Brazil

Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) are acute and potentially fatal inflammatory vesiculobullous reactions that affect the skin and mucous membranes, and which are most often triggered by particular medications and infections. In Brazil, the drugs most frequently associated with TEN and SJS include cold medicine such as dipyrone and NSAIDs, followed by carbamazepine, phenobarbital, penicillin, and allopurinol. Genetic variations have been found to increase the risk of SJS/TEN in response to triggering factors such as medications. The most closely associated genes found in Brazilian cold-medicine-related SJS/TEN patients with severe ocular complications are HLA-A^*66:01 in those of mixed African and European ancestry and HLA-B^*44:03 and HLA-C^*12:03 in those of solely European ancestry. Our classification system for grading ocular surface complication severity in SJS/TEN patients revealed the most severe complications to be limbal stem cell deficiency and dry eye. Changes to the conjunctival flora have also been observed in SJS/TEN patients. Our group identified bacterial colonization in 95% of the eyes (55.5% of which were gram-positive cocci, 25.5% of which were gram-negative bacilli, and 19% of which were gram-positive bacilli). Several new treatment options in the acute and chronic ocular management of the SJS/TEN patients have been described. This article highlights some Brazilian institutions' contributions to ocular surface care in both the acute phase (including the use of amniotic membrane transplantation) and the chronic phase (such as eyelid margin and fornix reconstruction, minor salivary gland transplantation, amniotic membrane and limbal transplantation, scleral contact lenses, anti-angiogenic eyedrops for corneal neovascularization, ex-vivo cultivated limbal epithelium transplantation, conjunctival-limbal autografting, oral mucosa transplantation, and keratoprosthesis).

Cascade of Inflammatory, Fibrotic Processes, and Stress-Induced Senescence in Chronic GVHD-Related Dry Eye Disease

Ocular graft-versus-host disease (GVHD) is a major complication after allogeneic hematopoietic stem cell transplantation. Ocular GVHD affects recipients' visual function and quality of life. Recent advanced research in this area has gradually attracted attention from a wide range of physicians and ophthalmologists. This review highlights the mechanism of immune processes and the molecular mechanism, including several inflammation cascades, pathogenic fibrosis, and stress-induced senescence related to ocular GVHD, in basic spectrum topics in this area. How the disease develops and what kinds of cells participate in ocular GVHD are discussed. Although the classical immune process is a main pathological pathway in this disease, senescence-associated changes in immune cells and stem cells may also drive this disease. The DNA damage response, p16/p21, and the expression of markers associated with the senescence-associated secretory phenotype (SASP) are seen in ocular tissue in GVHD. Macrophages, T cells, and mesenchymal cells from donors or recipients that increasingly infiltrate the ocular surface serve as the source of increased secretion of IL-6, which is a major SASP driver. Agents capable of reversing the changes, including senolytic reagents or those that can suppress the SASP seen in GVHD, provide new potential targets for the treatment of GVHD. Creating innovative therapies for ocular GVHD is necessary to treat this intractable ocular disease.

The Ocular Microbiome in Stevens-Johnson Syndrome

The ocular surface microbiome is an essential factor that maintains ocular surface homeostasis. Since the ocular surface is continuously exposed to the external environment, its microbiome, tears, and local immunity are vital for maintaining normal conditions. Additionally, this microbiome helps prevent pathogen colonization, which commonly leads to opportunistic infection. The abnormal ocular surface microbiome has previously been reported in several conditions, including dry eyes, allergy, blepharitis, graft-versus-host disease (GVHD), and Stevens-Johnson syndrome (SJS). Several approaches were applied to identify the ocular microbiome, including conventional culture techniques and molecular sequencing techniques. By using 16s rRNA sequencing, alterations in the type, proportion, and composition of bacterial communities, described by alpha (α)-and beta (β)-diversity, were observed in SJS patients compared to the healthy group. Conventional culture techniques indicated a higher number of positive bacterial cultures in the SJS group, with a predominance of gram-positive cocci and gram-positive bacilli. Besides, there are increased variations and multiple detections of bacterial genera. Taken together, SJS causes structural changes in the ocular surface and significantly affects its microbiome. Further studies into the area of temporal relationship, metagenomics, proteomics, and metabolomics analysis of the microbiome will lead to a better understanding of this disease. Finally, the treatment using prebiotics and probiotics to re-establish the normal ocular ecosystem and bring back a healthy ocular surface await confirmation.

Associations Between Stevens-Johnson Syndrome and Infection: Overview of Pharmacoepidemiological Studies

Stevens-Johnson syndrome and toxic epidermal necrolysis (SJS/TEN) are classified as type B adverse drug reactions, and are severe, potentially fatal rare disorders. However, the pathogenesis of SJS/TEN is not fully understood. The onset of SJS/TEN is triggered by the immune system in response to antigens with or by drugs. As activation of the immune system is important, infection could be a risk factor for the onset of SJS/TEN. Based on the hypothesis that infections induce the onset of SJS/TEN, we conducted pharmacoepidemiological investigations using two spontaneous adverse drug reaction reporting databases (Japanese Adverse Drug Event Report database and Food and Drug Administration Adverse Event Reporting System) and Japanese medical information database. These data suggest that infection could be a risk factor for the development of SJS/TEN. In this mini-review, we discuss the association between infection and the development of SJS/TEN.

Comparative profile of ocular surface microbiome in vernal keratoconjunctivitis patients and healthy subjects

PURPOSE

To compare ocular surface microbiome and its antibiotic sensitivity in vernal keratoconjunctivitis (VKC) with normal ocular surface.

METHODS

In this case-control study, thirty patients each with clinical diagnosis of VKC and age-matched controls with normal ocular surface were enrolled. Tear film samples were collected from each group and subjected to microbial evaluation with microscopy, conventional culture methods, and polymerase chain reaction (PCR). Microbial diversity and antibiotic sensitivity patterns were analyzed.

RESULTS

Most patients (67%) belonged to severe grades (3 and 4) of VKC, and allergic history could be elicited in 20%. On culture, bacteria were isolated in 50% of VKC patients and 47% of control group. Staphylococcus species were identified in 70% VKC group and 57% control group. S. aureus growth was seen in 52% and 21% of VKC patients and controls, respectively. S. pneumoniae was isolated only in controls (29%) (p<0.05). Confluent colonies (≥10 colonies/μl) were seen in 70% of VKC patients and 14% of controls (p<0.05). Fluoroquinolone resistance was more among higher grades of VKC (50%) (p<0.01) and was observed in 46% of VKC patients and 23% of control group (p<0.01). Both groups were negative for HSV-1 DNA and fungal growth.

CONCLUSION

Staphylococcus, the most common ocular surface flora, was predominant in VKC patients. Microbial analysis revealed similar microbial diversity in both groups. However, bacterial load was higher in VKC. Increased fluoroquinolone resistance was observed in VKC patients with more resistance among higher grades. Fungi and HSV-1 were not seen in VKC or normal ocular surface.

Strain heterogeneity, cooccurrence network, taxonomic composition and functional profile of the healthy ocular surface microbiome

BACKGROUND

There is growing evidence indicating that the microbial communities that dwell on the human ocular surface are crucially important for ocular surface health and disease. Little is known about interspecies interactions, functional profiles, and strain heterogeneity across individuals in healthy ocular surface microbiomes.

METHODS

To comprehensively characterize the strain heterogeneity, cooccurrence network, taxonomic composition and functional profile of the healthy ocular surface microbiome, we performed shotgun metagenomics sequencing on ocular surface mucosal membrane swabs of 17 healthy volunteers.

RESULTS

The healthy ocular surface microbiome was classified into 12 phyla, 70 genera, and 140 species. The number of species in each healthy ocular surface microbiome ranged from 6 to 47, indicating differences in microbial diversity among individuals. The species with high relative abundances and high positivity rates were Streptococcus pyogenes, Staphylococcus epidermidis, Propionibacterium acnes, Corynebacterium accolens, and Enhydrobacter aerosaccus. A correlation network analysis revealed a competitive interaction of Staphylococcus epidermidis with Streptococcus pyogenes in ocular surface microbial ecosystems. Staphylococcus epidermidis and Streptococcus pyogenes revealed phylogenetic diversity among different individuals. At the functional level, the pathways related to transcription were the most abundant. We also found that there were abundant lipid and amino acid metabolism pathways in the healthy ocular surface microbiome.

CONCLUSION

This study explored the strain heterogeneity, cooccurrence network, taxonomic composition, and functional profile of the healthy ocular surface microbiome. These findings have important significance for the future development of probiotic-based eye therapeutic drugs.

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.

Alterations in the conjunctival surface bacterial microbiome in bacterial keratitis patients

Microbial keratitis is an infectious disease of the eye, in which the cornea is inflamed. Under severe conditions, keratitis can lead to significant loss of vision and enucleation of the eye. Ocular trauma is the major risk factor causing keratitis and microorganisms viz., bacteria, fungi, viruses are the causative agents. The current study characterized the conjunctival bacterial microbiomes of healthy individuals and individuals with bacterial keratitis (BK) and assessed whether ocular microbiome dysbiosis is prevalent in BK patients. Ocular bacterial microbiomes were generated from the conjunctival swabs of healthy controls (HC-SW) and conjunctival swabs (BK-SW) and corneal scrapings (BK-CR) of BK patients using V3-V4 amplicon sequencing and data analysed using QIIME and R software. The Alpha diversity indices, diversity and abundance of different phyla and genera, heat map analysis, NMDS plots and inferred functional pathway analysis clearly discriminated the bacterial microbiomes of conjunctival swabs of healthy controls from that of BK patients. Preponderance of negative interactions in the hub genera were observed in BK-CR and BK-SW compared to HC-SW. In addition, a consistent increase in the abundance of pathogenic bacteria, as inferred from published literature, was observed in the conjunctiva of BK patients compared to HC and this may be related to causing or exacerbating ocular surface inflammation. This is the first study demonstrating dysbiosis in the ocular bacterial microbiome of conjunctiva of bacterial keratitis patients compared to the eye of healthy controls. The bacterial microbiome associated with the corneal scrapings of keratitis individuals is also described for the first time.

Ocular Surface Microbiome in Health and Disease

The ocular surface is exposed continuously to the environment and, as a consequence, to a variety of different microbes. After the results of the Human Microbiome Project became publicly available, international research groups started to focus interest on exploring the ocular surface microbiome and its physiopathological relationship to the eye. For example, numerous research studies the existence of the ocular surface's bacterial flora, typically gathering cultures from healthy patients and finding few variations in the bacterial species. More recently, culture-independent methods, including 16S ribosomal ribonucleic acid (rRNA) gene sequencing, are being used to define the ocular microbiome. These newer methods suggest that the microbial communities have a greater diversity than previously reported. These communities seem to serve an immune-modulating function and maintain relationships with other microbes and organs, even distant ones. This review summarizes the literature exploring the ocular microbiome, both in health and in different diseases.