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[This corrects the article DOI: 10.1371/journal.pone.0199640.].

This was a retrospective cross-sectional study evaluating the aetiology and antibiotic susceptibility in patients treated for suspected bacterial keratitis at Skåne University Hospital during 2019. Inclusion criteria: eyes with bacterial keratitis. Exclusion criteria: co-infection with other microbes. Primary outcome parameters: predisposing factors, causative pathogens and antibiotic susceptibility. Secondary outcome parameter: antibiotic treatment. A total of 255 cases met the inclusion criteria. Of these, 149 (58%) occurred in contact lens wearers. Corneal cultures, when performed, were positive in 51% of cases. For eyes which had received antibiotic treatment prior to corneal culture (n = 36), the proportion of positive cultures was 50%. Ulcers < 1 mm were less likely to yield a positive culture than those ≥ 1 mm. The most frequently isolated bacteria were coagulase-negative staphylococci (48%). Antibiotic resistance rates were lowest to levofloxacin (0%), ciprofloxacin (2%) and chloramphenicol (4%), and highest to fusidic acid (47%) and clindamycin (19%). The low proportion of positive cultures from small ulcers suggests that these warrant a different diagnostic approach. Furthermore, corneal cultures from eyes with ongoing antibiotic treatment were positive to the same extent as those from untreated eyes, suggesting that discontinuation of antibiotic treatment before re-culturing might not be necessary.

Vermamoeba vermiformis ( V. vermiformis ) is one of the most common free-living amoeba (FLA) and is frequently found in environments such as natural freshwater areas, surface waters, soil, and biofilms. V. vermiformis has been reported as a pathogen with pathogenic potential for humans and animals . The aim is to report a case of non- Acanthamoeba keratitis in which V. vermiformis was the etiological agent, identified by culture and molecular techniques. Our case was a 48-year-old male patient with a history of trauma to his eye 10 days ago. The patient complained of eye redness and purulent discharge. A slit-lamp examination of the eye revealed a central corneal ulcer with peripheral infiltration extending into the deep stroma. The corneal scraping sample taken from the patient was cultured on a non-nutritious agar plate (NNA). Amoebae were evaluated according to morphological evaluation criteria. It was investigated by PCR method and confirmed by DNA sequence analysis. Although no bacterial or fungal growth was detected in the routine microbiological evaluation of the corneal scraping sample that was cultured, amoeba growth was detected positively in the NNA culture. Meanwhile, Acanthamoeba was detected negative by real-time PCR. However, V. vermiformis was detected positive with the specific PCR assay. It was confirmed by DNA sequence analysis to be considered an etiological pathogenic agent. Thus, topical administration of chlorhexidine gluconate %0.02 (8 × 1) was initiated. Clinical regression was observed 72 h after chlorhexidine initiation, and complete resolution of keratitis with residual scarring was noticed in 5 weeks. In conclusion, corneal infections due to free-living amoebae can occur, especially in poor hygiene. Although Acanthamoeba is the most common keratitis due to amoeba, V. vermiformis is also assumed to associate keratitis in humans. Clinicians should also be aware of other amoebic agents, such as V. vermiformis , in keratitis patients.

Fungal keratitis is a severe corneal infection that often results in blindness and eye loss. The disease is most prevalent in tropical and subtropical climates, and infected individuals are frequently young agricultural workers of low socioeconomic status. Early diagnosis and treatment can preserve vision. Here, we discuss the fungal keratitis diagnostic literature and estimate the global burden through a complete systematic literature review from January, 1946 to July, 2019. An adapted GRADE score was used to evaluate incidence papers—116 studies provided the incidence of fungal keratitis as a proportion of microbial keratitis and 18 provided the incidence in a defined population. We calculated a minimum annual incidence estimate of 1 051 787 cases (736 251–1 367 323), with the highest rates in Asia and Africa. If all culture-negative cases are assumed to be fungal, the annual incidence would be 1 480 916 cases (1 036 641–1 925 191). In three case series, 8–11% of patients had to have the eye removed, which represents an annual loss of 84 143–115 697 eyes. As fungal keratitis probably affects over a million people annually, an inexpensive, simple diagnostic method and affordable treatment are needed in every country.

Infectious keratitis (IK) represents a significant global health concern, ranking as the fifth leading cause of blindness worldwide despite being largely preventable and treatable. Elderly populations are particularly susceptible due to age-related changes in immune response and corneal structure. However, research on IK in this demographic remains scarce. Age-related alterations such as increased permeability and reduced endothelial cell density further compound susceptibility to infection and hinder healing mechanisms. Additionally, inflammaging, characterized by chronic inflammation that develops with advanced age, disrupts the ocular immune balance, potentially exacerbating IK and other age-related eye diseases. Understanding these mechanisms is paramount for enhancing IK management, especially in elderly patients. This review comprehensively assesses risk factors, clinical characteristics, and management strategies for bacterial, viral, fungal, and acanthamoeba keratitis in the elderly population, offering crucial insights for effective intervention.

Fungal keratitis caused by Candida albicans (CA) is a common, disabling eye disease with a complex immune response system, affecting diagnosis, treatment, and prognosis. The specific regulatory roles and interactions of IL-36γ and pigment epithelium-derived factor (PEDF) in this disease remain largely unclarified. Additionally, the influence of miR-204-5p on the expression and anti-inflammatory functions of IL-36γ and PEDF in CA keratitis is insufficiently explored. Therefore, research focused on understanding the disease’s pathogenesis and immune regulation. Human corneal epithelial cells treated with heat-killed CA showed anti-inflammatory responses from IL36γ and PEDF, confirmed via western blot, PCR, and ELISA. Transfection of small interfering RNA and recombinant protein granules showed PEDF exerts immunoprotected regulatory mechanisms by inhibiting NF-κB via PPARγ. Analysis of multiple miRNA target gene prediction databases and literature revealed that miR-204-5p is differentially expressed in fungal keratitis. PCR and dual luciferase reporter assays confirmed that miR-204-5p directly binds to PEDF mRNA, negatively regulating IL36γ and PEDF expression. Consequently, both PEDF and IL-36 γ exhibit anti-inflammatory effects in CA keratitis. PEDF may inhibit the NF-κB signaling pathway through the PPAR γ pathway. In addition, miR-204-5p inhibits the mRNA expression of IL-36 γ and PEDF, exacerbating inflammation. This provides a theoretical basis for new methods and drug targets for the prevention and treatment of CA keratitis, and promotes the clinical application of IL-36 γ/PEDF.

Contact lens wear is a common predisposing factor in microbial keratitis and is one of the two preventable risk factors for corneal infection in a working age population. Our understanding of the prevention and prophylaxis of contact lens-related corneal infection is informed by recent epidemiological studies describing the incidence of and risk factors for the disease, the effect of causative organism on disease severity, and an appreciation of individual immune profiles in susceptibility to and severity of the disease. Although contemporary contact lenses have not reduced the overall incidence of keratitis, a reduction in morbidity may be achievable through recognition of appropriate risk factors in severe disease, including avoiding delays in presenting for appropriate treatment, and attention to storage case hygiene practise. Severe keratitis is most commonly associated with an environmental causative organism, and daily disposable lenses are associated with less severe disease. Pseudomonas aeruginosa remains the commonest cause of contact lens-related corneal infection probably because of its unique virulence characteristics and ability to survive in the contact lens/storage case/ocular environment. In two recent outbreaks of contact lens-related infections, there has been a strong association demonstrated with particular contact lens solutions. Since the recall of these specific contact lens solutions, the rate of Acanthamoeba keratitis has remained above the expected baseline, indicating unidentified risk factors that may include environmental exposures. Individual differences in susceptibility to microbial keratitis may be partly explained by differences in single-nucleotide polymorphisms in certain cytokine genes, particularly those with a proven protective role in corneal infection.

To evaluate the incidence of Acanthamoeba keratitis in the Netherlands between 2009 and 2015 and to analyse predicting factors for treatment outcome. Patient characteristics, diagnostic methods, diagnostic delay, therapy prior to and after diagnosis, and visual outcome were obtained from medical files of all patients diagnosed with Acanthamoeba keratitis in the Netherlands between 2009 and 2015. A logistic regression analysis on treatment failure, defined as a best corrected visual acuity of less than 20/40 Snellen decimals (i.e. >0.3 logMAR or an approximate loss of three lines of visual acuity) and/or the need for keratoplasty, was performed to determine predicting factors. Two hundred and twenty-four eyes of 224 patients were included. Ninety-five percent of the patients were contact lens wearers, of whom 74% wore soft contact lenses. The number of cases increased from 16 in 2009 to 49 in 2015. This resulted in an estimated incidence of 1 in 21,000 for soft contact lens wearers in 2015. Eighty-seven eyes (39%) met the criteria for treatment failure. In a multivariable regression analysis, higher age at presentation, a higher severity stage and corticosteroid use before diagnosis were positively correlated with treatment failure. Early referral to a cornea specialist was associated with better clinical outcomes. Although Acanthamoeba keratitis is still a relatively uncommon disease, the incidence in soft contact lens wearers has increased to reach 1 in 21,000 in 2015. Treatment failure occurred in 39% of cases, with age, higher severity stage, corticosteroid use before diagnosis and indirect referral to a cornea specialist as important risks factors.

Purpose: To compare the costs associated with medications and travel of patients with smear-proven bacterial keratitis and fungal keratitis in a tertiary care center in India. Methods: Retrospective analysis of case records of a cohort of patients who presented between April 2017 and March 2018 to a tertiary care center in India, with infectious keratitis who were smear-positive for bacteria or fungi, and whose costs of treatment and travel were supported by a philanthropic program. Results: In total, 672 case records of 177 smear-positive bacterial keratitis (BK) and 495 smear-positive fungal keratitis (FK) were included in the study. Further, 62% of BK and 75% of FK received more than one antimicrobial drug (P < 0.001). The mean total medication cost (INR) was significantly more in FK (959.1 ± 675.2) compared to BK (674.9 ± 463.7) (P < 0.0001). The mean medication cost (INR) per visit was also more for FK (201.1 ± 109.4) compared to BK (155.2 ± 84.1) (P < 0.0001). The mean total medication cost was significantly more for FK for both patients who healed with medical treatment (611.6 ± 395.6 for BK, 801.5 ± 599.9 for FK, P = 0.0005) and for patients who required TPK (953.7 ± 653.1 for BK, 1374.6 ± 701.5 for FK, P = 0.0023) compared to their respective counterparts in BK Conclusion: Patients with fungal keratitis incurred significantly more on medications compared to patients with bacterial keratitis irrespective of whether they had healed with successful medical treatment or required therapeutic keratoplasty. Prolonged duration of treatment and the high costs of antifungal medications account for the significant economic burden of fungal keratitis.