Delhi Infectious Keratitis Study: Update on Clinico-Microbiological Profile and Outcomes of Infectious Keratitis

Immune Mechanisms of Filamentous Fungal Keratitis

Filamentous fungal keratitis is a particularly serious eye infection that often results in ulceration, corneal perforation, and blindness. The cornea acts as a natural barrier against harmful agents due to the close connection of its epithelial cells. In addition, on its surface, there is a large number of substances with anti-inflammatory and bactericidal properties, such as secretory IgA and mucin glycoproteins, and antimicrobial peptides (AMPs), such as human β-defensin 2 (HBD-2) and LL-37, which are especially increased in filamentous fungal keratitis. The interaction between pathogenic fungi and the host's immune mechanisms is a complex process: pathogen-associated molecular pattern (PAMP) molecules (chitin, β-glucan, and mannan) found in the fungal cell wall are recognized by pattern recognition receptors (PRRs) (toll-like receptors {TLRs}, C-type lectin receptors {CLRs}, nucleotide-binding oligomerization domain-like receptors {NLRs}, and scavenger receptors {SR}) found in host defense cells, triggering the secretion of various types of cytokines, such as interleukins (IL), tumor necrosis factors (TNFs), and chemokines, which recruit macrophages and neutrophils to migrate to the site of infection and activate inflammatory responses. In addition, the interaction of hyphae and corneal epithelial cells can activate cluster of differentiation (CD) 4+ T cells, CD8+ T cells, and B cells and induce secretion of T-helper (Th)-type cytokines 2 (IL-4 and IL-13) and IgG.

Spectrum and antibiotic sensitivity of bacterial keratitis: a retrospective analysis of eight years in a Tertiary Referral Hospital in Southwest China

Purpose

The objective of this study was to investigate the epidemiological characteristics, distribution of isolates, prevailing patterns, and antibiotic susceptibility of bacterial keratitis (BK) in a Tertiary Referral Hospital located in Southwest China.

Methods

A retrospective analysis was conducted on 660 cases of bacterial keratitis occurring between January 2015 and December 2022. The demographic data, predisposing factors, microbial findings, and antibiotic sensitivity profiles were examined.

Results

Corneal trauma emerged as the most prevalent predisposing factor, accounting for 37.1% of cases. Among these cases, bacterial culture results were positive in 318 cases, 68 species of bacteria were identified. The most common Gram-Positive bacteria isolated overall was the staphylococcus epidermis and the most common Gram-Negative bacteria isolated was Pseudomonas aeruginosa. Methicillin-Resistant Staphylococci accounted for 18.1% of all Gram-Positive bacteria. The detection rate of P. aeruginosa showed an increasing trend over time (Rs=0.738, P=0.037). There was a significant decrease in the percentage of Gram-Negative microorganisms over time (Rs=0.743, P=0.035). The sensitivity of Gram-Positive bacteria to linezolid, vancomycin, tigecycline, quinupristin/dalfopristin, and rifampicin was over 98%. The sensitivity rates of Gram-Negative bacteria to amikacin, meropenem, piperacillin/tazobactam, cefoperazone sodium/sulbactam, ceftazidime, and cefepime were all above 85%. In patients with a history of vegetative trauma, the possibility of BK should be taken into account in addition to the focus on fungal keratitis.

Conclusion

The microbial composition primarily consists of Gram-Positive cocci and Gram-Negative bacilli. Among the Gram-Positive bacteria, S. epidermidis and Streptococcus pneumoniae are the most frequently encountered, while P. aeruginosa is the predominant Gram-Negative bacteria. To combat Gram-Positive bacteria, vancomycin, linezolid, and rifampicin are considered excellent antimicrobial agents. When targeting Gram-Negative pathogens, third-generation cephalosporins exhibit superior sensitivity compared to first and second-generation counterparts. As an initial empirical treatment for severe cases of bacterial keratitis and those unresponsive to fourth-generation fluoroquinolones in community settings, the combination therapy of vancomycin and tobramycin is a justifiable approach. Bacterial keratitis can be better managed by understanding the local etiology and antibacterial drug susceptibility patterns.

Debulking corneal biopsy with tectonic amniotic membrane transplantation in refractory clinically presumed fungal keratitis

The treatment of fungal keratitis (FK) is challenging due to the subacute indolent course, and initial misdiagnosis. In this retrospective case series, we highlight both the diagnostic and therapeutic roles of corneal biopsy together with amniotic membrane transplantation (AMT) in patients with refractory clinically presumed FK. Debulking biopsy and tectonic AMT were performed during the initial presentation. Biopsy specimens were sent for KOH smears and cultures. After KOH smears confirmed the presence of fungal elements, topical voriconazole 1% was prescribed for the first 72 h then tailored according to the clinical response and the culture results. The outcome measures were complete resolution of infection and restoration of corneal integrity. Cases associated with culture proven bacterial keratitis were excluded. Twelve cases were included in the study. KOH smears confirmed the presence of fungal growth in all specimens. Cultures grew Aspergillus in 6/12 cases, sensitive to voriconazole (5/6) and amphotericin (3/6); Fusarium (4/12), sensitive to both voriconazole and amphotericin; and no growth in 2/12 cases. Amphotericin 0.15% eye drops were added to the 7 cases with proven sensitivity and to the remaining 2 culture negative cases. Gradual resolution of infection was seen in all cases after 35.6 ± 7.8 days. In FK, a debulking biopsy simultaneously with AMT help decrease the microbial load, suppress the inflammatory process, support the corneal integrity, confirm the presence of fungal pathogen.

Microbial keratitis and antibiotic sensitivity patterns: A retrospective analysis at a tertiary center in Central India

Purpose

To report on the microbiological profile and antibiotic sensitivity patterns of infectious keratitis at a tertiary center in central India.

Methods

The suspected case of severe keratitis underwent microbiological culture and identification using the VITEK 2 technique. Antibiotic susceptibility for different sensitivity and resistance patterns was analyzed. Demographics, clinical profile, and socioeconomic history was also documented.

Results

Culture was positive in 233/455 (51.2%) patients. Pure bacterial growth was present in 83 (35.62%) patients and pure fungus was present in 146 (62.66%) patients. The most common bacterial cause of infectious keratitis was Pseudomonas followed by Staphylococcus and Bacillus. Pseudomonas showed 65%-75% resistance against levofloxacin, ceftazidime, imipenem, gentamycin, ciprofloxacin, and amikacin. Staphylococcus showed 65%-70% resistance against levofloxacin, erythromycin, and ciprofloxacin, with Streptococcus being 100% resistant to erythromycin.

Conclusion

This study highlights the current trend of microbiological profiles of infectious keratitis and their antibiotic susceptibility at a rural setup in central India. Fungal predominance and increased resistance against the commonly used antibiotics were noted.

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.

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.

Ciprofloxacin resistance and tolerance of Pseudomonas aeruginosa ocular isolates

PURPOSE

Tolerance to antibiotics may occur due to changes in bacterial growth patterns and can be a precursor to development of resistance. However, there is a lack of information on the ability of ocular bacteria isolates to develop tolerance. This paper explores the tolerance to 8 different antibiotics of 61 microbial keratitis isolates of Pseudomonas aeruginosa from Australia and India using the MBC/MIC ratio, with tolerance defined by a ratio ≥ 32, and tolerance to ciprofloxacin by an agar diffusion assay.

METHODS

Antibiotics used were ciprofloxacin, levofloxacin, gentamicin, tobramycin, piperacillin, imipenem, ceftazidime and polymyxin B. Isolates were sourced from microbial keratitis infections in Australia and India. Minimum bactericidal and minimum inhibitory concentration (MBC and MIC) were obtained using broth microdilution and compared to breakpoints from the Clinical Laboratory Standards Institute (CLSI) and European Committee on Antimicrobial Susceptibility Testing (EUCAST) to determine bacterial susceptibility. Tolerance was assessed as MBC/MIC ≥ 32. An alternative method for tolerance detection (TD) was assessed with 13P. aeruginosa sensitive isolates by agar disk diffusion assay of ciprofloxacin followed by application of glucose to the agar and observation of re-growth of colonies.

RESULTS

Thirty-three isolates were resistant to imipenem, 20 to ciprofloxacin, 14 to tobramycin and piperacillin, 12 to levofloxacin and ceftazidime, 8 to gentamicin, and 5 to polymyxin B. The percentage of strains resistant to levofloxacin (7 vs 30 %; p = 0.023), gentamicin (0 vs 24 %; p = 0.005) and tobramycin (4 vs 33 %; p = 0.004) was significantly greater in isolates from India.On average, strains from India exhibited notably greater MIC and MBC values compared to strains obtained from Australia. Out of 61 isolates, none displayed an MBC/MIC ratio ≥ 32. However, three sensitive isolates had low tolerance, nine had medium tolerance and one had high tolerance to ciprofloxacin with the TDtest.

CONCLUSIONS

This study used two methods to determine whether P. aeruginosa strains could show tolerance to antibiotics. Using the MBC/MIC criteria no strain was considered tolerant to any of the eight antibiotics used. When 13 strains were tested for tolerance against ciprofloxacin, the most commonly used monotherapy for keratitis, one had high tolerance and nine had medium tolerance. This demonstrates the capacity of P. aeruginosa to develop tolerance which may result in therapeutic failures if inappropriate dosing regimens are used to treat keratitis.

Spectrum of bacterial keratitis in North India: A retrospective analysis of six years at a tertiary care eye center

Purpose

To analyze the pattern of bacterial pathogens causing infective keratitis and their resistance to the recommended antibiotics over six years.

Methods

It was a retrospective study of 9,357 cases of bacterial keratitis from January 2015 to December 2020, at a tertiary care ophthalmic center. A total of 9,547 corneal specimens were obtained from the study subjects. Demographic details of the patients, pathogenic bacteria isolated, and their antimicrobial susceptibility were noted and analyzed.

Results

Bacterial pathogens were identified in 23.52% of the specimens. The most common isolates were coagulase-negative Staphylococci (60.75%), followed by Pseudomonas aeruginosa (14.23%), Staphylococcus aureus (13.92%), gram negative bacilli of the family Enterobacterales (8.64%), Streptococcus spp. (1.72%), Acinetobacter spp. (0.13%), and other non-fermenting gram-negative bacilli (0.57%). In Staphylococci, 55-80% of isolates were resistant to erythromycin, and 40-70% to fluoroquinolones, while no resistance was observed against vancomycin. 40-60% of isolates of P. aeruginosa were resistant to cephalosporins, 40-55% to fluoroquinolones, and 30-60% to aminoglycosides. Also, 40-80% of isolates of Enterobacterales were resistant to cephalosporins, and 50-60% to fluoroquinolones. Most gram-negative isolates were susceptible to carbapenems and polymyxin B.

Conclusion

To the best of our knowledge, our study is the largest compilation of microbiological profile of bacterial keratitis from North India. It highlights the current trend of the bacterial pathogens that cause infectious keratitis. Staphylococci and Pseudomonas were found to be the most common pathogens. Increased resistance was seen against some of the commonly prescribed empirical antibiotics. Such evidence is useful for restructuring the empirical prescription practices from time to time.

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.

Infectious Keratitis: An Update on Role of Epigenetics

Epigenetic mechanisms modulate gene expression and function without altering the base sequence of DNA. These reversible, heritable, and environment-influenced mechanisms generate various cell types during development and orchestrate the cellular responses to external stimuli by regulating the expression of genome. Also, the epigenetic modifications influence common pathological and physiological responses including inflammation, ischemia, neoplasia, aging and neurodegeneration etc. In recent past, the field of epigenetics has gained momentum and become an increasingly important area of biomedical research As far as eye is concerned, epigenetic mechanisms may play an important role in many complex diseases such as corneal dystrophy, cataract, glaucoma, diabetic retinopathy, ocular neoplasia, uveitis, and age-related macular degeneration. Focusing on the epigenetic mechanisms in ocular diseases may provide new understanding and insights into the pathogenesis of complex eye diseases and thus can aid in the development of novel treatments for these diseases. In the present review, we summarize the clinical perspective of infectious keratitis, role of epigenetics in infectious keratitis, therapeutic potential of epigenetic modifiers and the future perspective.

Fungal Endophthalmitis: A Comprehensive Review

Endophthalmitis is a serious ophthalmologic condition involving purulent inflammation of the intraocular spaces. The underlying etiology of infectious endophthalmitis is typically bacterial or fungal. The mechanism of entry into the eye is either exogenous, involving seeding of an infectious source from outside the eye (e.g., trauma or surgical complications), or endogenous, involving transit of an infectious source to the eye via the bloodstream. The most common organism for fungal endophthalmitis is Candida albicans. The most common clinical manifestation of fungal endophthalmitis is vision loss, but other signs of inflammation and infection are frequently present. Fungal endophthalmitis is a clinical diagnosis, which can be supported by vitreous, aqueous, or blood cultures. Treatment involves systemic and intravitreal antifungal medications as well as possible pars plana vitrectomy. In this review, we examine these essential elements of understanding fungal endophthalmitis as a clinically relevant entity, which threatens patients’ vision.

Impact of COVID-19 Pandemic on Infectious Keratitis Outcomes: A Retrospective Multicenter Study in Tertiary Eye Hospitals of South India

PURPOSE

The purpose of this study was to report the adverse effects of the COVID-19 pandemic on the clinical outcomes of infectious keratitis in South India.

METHODS

Two hundred fifty-eight patients presented with infectious keratitis at 6 tertiary care centers when strict travel restrictions were in place from March 24 to May 31, 2020. Case records were collected retrospectively and analyzed for demographics, type of initial treatment, length of delay in presentation, microbiological diagnosis, clinical course, and final treatment outcome.

RESULTS

The mean age of the patients was 49.2 years, with most of them (61.2%) being male. Forty-one patients (15.9%) did not receive any treatment for at least a week after the onset of symptoms. One hundred eight patients (41.9%) presented with severe ulcer (32 had a frank perforation). Resolution of the infection was achieved only in 103 patients (45.6%). A total of 90 patients (39.8%) with ulcers had a perforation, yet only 29 patients (32.2%) could receive keratoplasty because of the unavailability of donor tissues. At the end of 6-month follow-up, 47 patients had anatomical failure (loss of globe) and 12 additional patients had functional failure (total permanent vision loss).

CONCLUSIONS

Delay in presentation and acute shortage of donor corneal tissues for emergency keratoplasty because of the COVID-19 pandemic had a grave impact, resulting in irreversible blindness in a significant number of patients.