Identification of causative pathogens in mouse eyes with bacterial keratitis by sequence analysis of 16S rDNA libraries

Alterations of the bacterial ocular surface microbiome are found in both eyes of horses with unilateral ulcerative keratitis

Next generation sequencing (NGS) studies in healthy equine eyes have shown a more diverse ocular surface microbiota compared to culture-based techniques. This study aimed to compare the bacterial ocular surface microbiota in both eyes of horses with unilateral ulcerative keratitis (UK) with controls free of ocular disease. Conjunctival swabs were obtained from both ulcerated eyes and unaffected eyes of 15 client-owned horses with unilateral UK following informed consent, as well as from one eye of 15 healthy horses. Genomic DNA was extracted from the swabs and sequenced on an Illumina platform using primers that target the V4 region of bacterial 16S rRNA. Data were analyzed using Quantitative Insights Into Molecular Ecology (QIIME2). The ocular surface of ulcerated eyes had significantly decreased species richness compared with unaffected fellow eyes (Chao1 q = 0.045, Observed ASVs p = 0.045) with no differences in evenness of species (Shannon q = 0.135). Bacterial community structure was significantly different between either eye of horses with UK and controls (unweighted UniFrac: control vs. unaffected, p = 0.03; control vs. ulcerated, p = 0.003; unaffected vs. ulcerated, p = 0.016). Relative abundance of the gram-positive taxonomic class, Bacilli, was significantly increased in ulcerated eyes compared with controls (q = 0.004). Relative abundance of the taxonomic family Staphylococcaceae was significantly increased in ulcerated and unaffected eyes compared with controls (q = 0.030). The results suggest the occurrence of dysbiosis in infected eyes and reveal alterations in beta diversity and taxa of unaffected fellow eyes. Further investigations are necessary to better understand the role of the microbiome in the pathophysiology of ocular surface disease.

Challenges and insights in the exploration of the low abundance human ocular surface microbiome

Purpose

The low microbial abundance on the ocular surface results in challenges in the characterization of its microbiome. The purpose of this study was to reveal factors introducing bias in the pipeline from sample collection to data analysis of low-abundant microbiomes.

Methods

Lower conjunctiva and lower lid swabs were collected from six participants using either standard cotton or flocked nylon swabs. Microbial DNA was isolated with two different kits (with or without prior host DNA depletion and mechanical lysis), followed by whole-metagenome shotgun sequencing with a high sequencing depth set at 60 million reads per sample. The relative microbial compositions were generated using the two different tools MetaPhlan3 and Kraken2.

Results

The total amount of extracted DNA was increased by using nylon flocked swabs on the lower conjunctiva. In total, 269 microbial species were detected. The most abundant bacterial phyla were Actinobacteria, Firmicutes and Proteobacteria. Depending on the DNA extraction kit and tool used for profiling, the microbial composition and the relative abundance of viruses varied.

Conclusion

The microbial composition on the ocular surface is not dependent on the swab type, but on the DNA extraction method and profiling tool. These factors have to be considered in further studies about the ocular surface microbiome and other sparsely colonized microbiomes in order to improve data reproducibility. Understanding challenges and biases in the characterization of the ocular surface microbiome may set the basis for microbiome-altering interventions for treatment of ocular surface associated diseases.

Poloxamer and Chitosan-Based In Situ Gels Loaded with Orthosiphon stamineus Benth. Extracts Containing Rosmarinic Acid for the Treatment of Ocular Infections

Objectives

Orthosiphon stamineus Benth. (OS) is a commonly used medicinal plant for curbing bacterial infections globally. This work aimed to fabricate poloxamer and chitosan-based in situ gels loaded with standardized aqueous-ethanolic OS leaf extracts and investigate their antimicrobial efficacy as a potential remedy against ocular infections.

Materials and Methods

In situ gels containing 0.5% w/v OS extract prepared using cold dispersion method were subjected to physicochemical characterization, including in vitro-release studies. Antimicrobial efficacy was tested against Staphylococcus aureus, Micrococcus luteus, Escherichia coli, and Pseudomonas aeruginosa using agar diffusion method.

Results

Thin layer chromatography and high performance liquid chromatography chromatograms confirmed the presence of rosmarinic acid (RA) and sinensitin in OS extracts with same retention factor (0.26 and 0.49) and retention times (12.2 and 20.7 min) against reference standards. A homogenous brown coloured in situ gel exhibited low viscosity as a solution and increased viscosity in gel form at ocular temperature. The optimized formulations, P7 (21% P407/4% P188), P8 (21% P407/5% P188) and F5 (1.5% chitosan and 45% β-glycerophosphate) exhibited ideal ocular pH (7.27-7.46), phase transition at ocular temperature (33-37°C) and prolonged RA release up to 12 h. Formulation F5 showed an inhibition zone of 4.3 mm against M. luteus.

Conclusion

Among all, formulation F5 alone exhibited modest antimicrobial activity against M. luteus. OS extracts at 5% and 10% were most active against tested bacteria however, loading them into in situ gels resulted in sedimentation. Hence, isolation of RA from OS extract is suggested before loading into formulations for a better antimicrobial activity.

Isolation of Streptococcus cuniculi from corneal lesion in laboratory-raised mice

Corneal lesions appearing as white mass beneath intact epithelium, with ocular discharge in one mouse, was observed in a batch of laboratory-raised BALB/c mice (n=9 of 56). The affected mice remained active, well-groomed and had normal appetite. Isolates recovered from swab cultures of the external and internal contents of the eye had partial 16S rRNA gene sequence of 99.1% similarity to Streptococcus cuniculi. No previous report of S. cuniculi infection in laboratory rodents has been presented. The isolate was susceptible to all antibiotics tested. We suggest S. cuniculi is an opportunistic bacteria in laboratory mice but are uncertain of its source. Our findings revealed that S. cuniculi is able to colonize laboratory mice and should be considered when mice present with eye lesion or ocular discharge.

Relationship between the microbiome and ocular health

The microbiome is important to the host as a whole, both in maintenance of health and in the pathophysiology of disease. The purpose of this review is to explore the relationship between the gut, ocular microbiome, and ocular disease states. We will also discuss how the microbiome can serve as a potential target for treatment, by methods such as modulation of diet, probiotics and fecal microbiota transplantation. The information discussed in the review has been gathered using literature published from 2004 to November 2018, as indexed in PubMed.

The anti-inflammatory effects of asiatic acid in lipopolysaccharide-stimulated human corneal epithelial cells

AIM

To investigate the anti-inflammatory effects of asiatic acid (AA) on lipopolysaccharide (LPS)-induced inflammatory response in human corneal epithelial cells (HCECs).

METHODS

Cell viability was measured using a cell counting kit-8 (CCK-8) assay. Quantitative real-time polymerase chain reaction (qRT-PCR) was used to determine the mRNA expression of interleukin-8 (IL-8), interleukin-6 (IL-6), interleukin-1β (IL-1β), tumor necrosis factor-alpha (TNF-α), and transforming growth factor-β (TGF-β) in HCECs. Intracellular reactive oxygen species (ROS) was measured using the ROS assay kit. Glutathione (GSH) concentration was measured using the total GSH assay kit. Akt1 and Akt phosphorylation (p-Akt1) levels were measured by Western blotting and immunofluorescence.

RESULTS

AA induced toxicity at high concentrations and significantly stimulated the proliferation of HCECs at concentrations of 20 µmol/L for 1h. LPS at concentrations of 300 ng/mL for 1h significantly stimulated the mRNA expression of IL-8, IL-6, IL-1β, TNF-α, and TGF-β in HCECs, while the stimulation effects were significantly inhibited by AA (20 µmol/L). In addition, AA was found to decrease the content of ROS, increase GSH generation, and also inhibit LPS-induced p-Akt in HCECs.

CONCLUSION

AA decreases the generation of inflammatory factors IL-8, IL-6, IL-1β, TNF-α, and TGF-β in LPS-stimulated HCECs. AA significantly inhibites the intracellular concentrations of ROS and increases GSH generation. AA also inhibites LPS-induced p-Akt in HCECs. These findings reveal that AA has anti-inflammation effects in LPS-stimulated HCECs.