Diagnosis of Fusarium keratitis in an animal model using the polymerase chain reaction

Innate Immune System Activation, Inflammation and Corneal Wound Healing

Corneal wounds resulting from injury, surgeries, or other intrusions not only cause pain, but also can predispose an individual to infection. While some inflammation may be beneficial to protect against microbial infection of wounds, the inflammatory process, if excessive, may delay corneal wound healing. An examination of the literature on the effect of inflammation on corneal wound healing suggests that manipulations that result in reductions in severe or chronic inflammation lead to better outcomes in terms of corneal clarity, thickness, and healing. However, some acute inflammation is necessary to allow efficient bacterial and fungal clearance and prevent corneal infection. This inflammation can be triggered by microbial components that activate the innate immune system through toll-like receptor (TLR) pathways. In particular, TLR2 and TLR4 activation leads to pro-inflammatory nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB) activation. Similarly, endogenous molecules released from disrupted cells, known as damage-associated molecular patterns (DAMPs), can also activate TLR2, TLR4 and NFκB, with the resultant inflammation worsening the outcome of corneal wound healing. In sterile keratitis without infection, inflammation can occur though TLRs to impact corneal wound healing and reduce corneal transparency. This review demonstrates the need for acute inflammation to prevent pathogenic infiltration, while supporting the idea that a reduction in chronic and/or excessive inflammation will allow for improved wound healing.

PR-1-Like Protein as a Potential Target for the Identification of Fusarium oxysporum: An In Silico Approach

Fusarium oxysporum remains one of the leading causes of economic losses and poor crop yields; its detection is strained due to its presentation in various morphological and physiological forms. This research work sought to identify novel biomarkers for the detection of Fusarium oxysporum using in silico approaches. Experimentally validated anti-Fusarium oxysporum antimicrobial peptides (AMPs) were used to construct a profile against Fusarium oxysporum. The performance and physicochemical parameters of these peptides were predicted. The gene for the Fusarium oxysporum receptor protein PR-1-like Protein, Fpr1, was identified and translated. The resulting protein model from the translation was then validated. The anti-Fusarium oxysporum AMPs and Fusarium oxysporum receptor protein 3-D structures were characterized, and their docking interaction analyses were carried out. The HMMER in silico tool identified novel anti-Fusarium oxysporum antimicrobial peptides with good performance in terms of accuracy, sensitivity, and specificity. These AMPs also displayed good physicochemical properties and bound with greater affinity to Fusarium oxysporum protein receptor PR-1-like Protein. The tendency of these AMPs to precisely detect Fusarium oxysporum PR-1-like Protein, Fpr1, would justify their use for the identification of the fungus. This study would enhance and facilitate the identification of Fusarium oxysporum to reduce problems associated with poor crop yield, economic losses, and decreased nutritional values of plants to keep up with the growing population.

Animal models of invasive mycoses

Animal models of invasive fungal infections have been developed and are applied in a huge number of different animal species for a number of research purposes, for example, the study of pathogenesis, defense mechanisms, and therapeutic strategies. From the different models, which in most cases are based on the same fungal species and often the same strain, as in spontaneous human infections, fundamental results and knowledge of the diagnosis, progression, prophylaxis, and therapy have been achieved. However, in all models, one should be critical with respect to mimicking the disease entity of humans, which is often the focus of the research. In many of the models for instance, the time course is different to the one of humans, and in others, the propensity for localization and containment in specific organs does not parallel the situation in humans. Nevertheless, many animal models of invasive mycoses have proven valuable in a number of research areas. With regard to new generations of anti-mycotic drugs, the models play an essential role in demonstrating antifungal activity, as well as in demonstrating the absence of toxic side effects, a critical step which cannot be accomplished by in vitro studies.

Filamentous fungal infections of the cornea: a global overview of epidemiology and drug sensitivity

Fungal keratitis is a serious suppurative, usually ulcerative corneal infection which may result in blindness or reduced vision. Epidemiological studies indicate that the occurrence of fungal keratitis is higher in warm, humid regions with agricultural economy. The most frequent filamentous fungal genera among the causal agents are Fusarium, Aspergillus and Curvularia. A more successful therapy of fungal keratitis relies on precise identification of the pathogen to the species level using molecular tools. As the sequence analysis of the internal transcribed spacer (ITS) region of the ribosomal RNA gene cluster (rDNA) is not discriminative enough to reveal a species-level diagnosis for several filamentous fungal species highly relevant in keratitis infections, analysis of other loci is also required for an exact diagnosis. Molecular identifications may also reveal the involvement of fungal species which were not previously reported from corneal infections. The routinely applied chemotherapy of fungal keratitis is based on the topical and systemic administration of polyenes and azole compounds. Antifungal susceptibility testing of the causal agents is of special importance due to the emergence and spread of resistance. Testing the applicability of further available antifungals and screening for new, potential compounds for the therapy of fungal keratitis are of highlighted interest.

A novel rat contact lens model for Fusarium keratitis

PURPOSE

The aim of this study was to develop and characterize a new contact lens-associated fungal keratitis rat model and to assess the ability of non-invasive spectral-domain optical coherence tomography (SD-OCT) to detect pathological changes in vivo in fungal keratitis.

METHODS

We used SD-OCT to image and measure the cornea of Sprague Dawley rats. Fusarium infection was initiated in the rat eye by fitting Fusarium solani-soaked contact lenses on the experimental eye, while the control animals received contact lenses soaked in sterile saline. The fungal infection was monitored with periodic slit-lamp examination and in vivo SD-OCT imaging of the rat eye, and confirmed by histology, counting of viable fungi in the infected rat cornea, and PCR with specific primers for Fusarium sp.

RESULTS

We imaged and measured the rat cornea with SD-OCT. Custom-made contact lenses were developed based on the OCT measurements. Incubation of contact lenses in a F. solani suspension resulted in biofilm formation. We induced contact lens-associated Fusarium keratitis by fitting the rat eyes for 4 h with the Fusarium-contaminated contact lenses. The SD-OCT images of the cornea correlated well with the slit-lamp and histopathological results and clearly defined clinical signs of infection, namely, increased corneal thickening, loss of epithelial continuity, hyper-reflective areas representing infiltrates, and endothelial plaques characteristic of fungal infection. Moreover, in three cases, SD-OCT detected the infection without any clear findings on slit-lamp examination. Infection was confirmed with histological fungal staining, PCR, and microbiological culture positivity.

CONCLUSIONS

We developed a highly reproducible rat contact lens model and successfully induced contact lens-associated Fusarium keratitis in this model. The clinical presentation of contact lens-associated Fusarium keratitis in the rat model is similar to the human condition. SD-OCT is a valuable tool that non-invasively revealed characteristic signs of the fungal infection and could provide sensitive, objective monitoring in fungal keratitis.

PCR for the molecular diagnosis of mycotic keratitis

Mycotic keratitis, an infection of the cornea caused by fungi, is a medical emergency, with patients presenting with considerable pain and distress. For effective management of the condition, a specific diagnosis must be made rapidly to permit early initiation of antifungal therapy. Currently, direct microscopic examination and culture of corneal material constitute the 'gold standard' for diagnosis. However, rapid, sensitive yet specific tests are needed to detect a small number of, or nonviable, fungi. PCR has many potential advantages when used as a diagnostic aid for mycotic keratitis; the present review covers these advantages, and possible limitations. An expert assessment is also made of studies that have used PCR for the diagnosis of mycotic keratitis. The review concludes with a Five-year view of the potential impact of PCR in management of mycotic keratitis.

Treatment of fungal keratitis from Fusarium infection by corneal cross-linking

PURPOSE

To evaluate the efficacy of corneal cross-linking (CXL) (riboflavin-UV-A) as a simple therapy in Fusarium keratitis.

METHODS

Twenty-four rabbits were systemically anesthetized, and the stromata of their right corneas were inoculated with Fusarium solani [10(5) colony-forming units (CFU) per milliliter]. Rabbits were divided into 2 groups: one was treated with CXL 72 hours after infection and the other did not receive any treatment (control). All eyes in both the groups were examined before (days 0 and 3) and after (day 7) CXL treatment. The eyes were enucleated, and corneal buttons were sent for microbiological and histological examinations.

RESULTS

All animals developed Fusarium keratitis; there was no statistically significant difference between groups before treatment (day 0, P = 0.397 and day 3, P = 0.702). After CXL treatment, the difference in clinical scores on day 7 between groups was statistically significant (P = 0.00); the CXL group showed significant lower clinical score. The CXL group had 22.45 ± 5.09 CFU/g compared with 42.5 ± 3.12 CFU/g in the control group; this difference was statistically significant (P = 0.01). In the 3 buttons of the control group, similar amounts of Fusarium hyphae and inflammatory cells were observed. In 2 of the 3 buttons analyzed from the CXL group, fewer Fusarium hyphae, inflammatory cells, and nonspecific stromal changes were observed compared with the control group.

CONCLUSIONS

Treatment of fungal keratitis with CXL seems to be effective in decreasing the intensity and severity of infectious keratitis by F. solani. This therapy may be useful as a coadjuvant in the medical treatment of resistant infections.

Evaluation of molecular diagnosis in fungal keratitis. Ten years of experience

Purpose

The aims of this study were to assess the utility of polymerase chain reaction (PCR) in diagnosing fungal keratitis in the last decade in our center and to review the molecular diagnosis of mycotic keratitis.

Methods

A retrospective nonrandomized investigation was undertaken at Vissum Corporación Instituto Oftalmologico de Alicante to evaluate 27 corneal samples of 20 patients with proven fungal keratitis from January 2000 to December 2009. Corneal samples (21 corneal scrapings, 5 biopsies, and 1 cornea) were evaluated by Gram stain or calcofluor stain, culture, and PCR. The detection and molecular identification were carried out by DNA amplification and sequencing of the internal transcribed spacer and 5.8S rRNA region from the corneal samples.

Results

PCR detected all the samples that were positive by conventional methods. Four samples were positive by PCR and showed negative results by culture and stain. Combination of microscopy and culture gave positive results in 21 of the 27 samples of patients with mycotic keratitis. Stains showed a 66.7% of positive results, culture showed 59.3%, and PCR showed 92.6%. The time taken for PCR assay was 4 to 8 h whereas positive fungal cultures took 1 to 35 days. Identification at species level by molecular methods was possible in all cases except one. Identification at species level by conventional methods only was possible in eight cases.

Conclusions

PCR not only proved to be an effective rapid method for the diagnosis of fungal keratitis but was also more sensitive than stain and culture methods. Fungal PCR must be added as the screening diagnosis test when an early mycotic keratitis is suspected. Molecular identification is the gold standard technique for the identification of corneal fungal pathogens.

Rapid polymerase chain reaction diagnosis of white-nose syndrome in bats

A newly developed polymerase chain reaction (PCR)-based method to rapidly and specifically detect Geomyces destructans on the wings of infected bats from small quantities (1-2 mg) of tissue is described in the current study (methods for culturing and isolating G. destructans from bat skin are also described). The lower limits of detection for PCR were 5 fg of purified fungal DNA or 100 conidia per 2 mg of wing tissue. By using histology as the standard, the PCR had a diagnostic specificity of 100% and a diagnostic sensitivity of 96%, whereas the diagnostic sensitivity of culture techniques was only 54%. The accuracy and fast turnaround time of PCR provides field biologists with valuable information on infection status more rapidly than traditional methods, and the small amount of tissue required for the test would allow diagnosis of white-nose syndrome in live animals.

Activation of Toll-like receptors 2 and 4 in Aspergillus fumigatus keratitis

Toll-like receptor (TLR) 2 and TLR4 are major receptors of Aspergillus fumigatus. Aspergillus fumigatus signaling in cornea induces the production of many pro-inflammatory molecules. In this study, we have shown that exposure of telomerase-immortalized human corneal epithelial cells (HCECs) to A. fumigatus antigens resulted in up-regulation of TLR2 and TLR4, and release of IL-1beta and IL-10 in HCECs, effects that could be inhibited by treatment with TLR2, and TLR4 antibodies. In addition, the A. fumigatus antigens-induced production of IL-1beta and IL-10 in supernatants of corneal epithelial cells was also attenuated by NF-kappaB inhibitor. Aspergillus fumigatus keratitis developed in Wistar rats, as evidenced by high SLE scores, influx of polymorphonuclear leukocytes (PMNs), activation of TLR2 and TLR4, and production of IL-1beta and IL-10 over controls. These findings indicate that the cornea has functional TLR2 and TLR4, and activation of TLR2 and TLR4 through NF-kappaB may contribute to pathogenesis of keratomycosis.

Specific detection of fungal pathogens by 18S rRNA gene PCR in microbial keratitis

Background

The sensitivity and specificity of 18S rRNA polymerase chain reaction (PCR) in the detection of fungal aetiology of microbial keratitis was determined in thirty patients with clinical diagnosis of microbial keratitis.

Methods

Corneal scrapings from patients were used for Gram stain, culture and PCR analysis. PCR was performed with primer pairs targeted to the 18S rRNA gene. The result of the PCR was compared with conventional culture and Gram staining method. The PCR positive samples were identified by DNA sequencing of the internal transcribed spacer (ITS) region of the rRNA gene. Main outcome measures were sensitivity and specificity of PCR in the detection of fungus in corneal keratitis.

Results

Combination of microscopy and culture gave a positive result in 11 of 30 samples of microbial keratitis. PCR detected 10 of 11 samples that were positive by conventional method. One of the 19 samples that was negative by conventional method was positive by PCR. Statistical analysis revealed that the PCR to have a sensitivity of 90.9% and specificity of 94.7% in the detection of a fungal aetiology in microbial keratitis.

Conclusion

PCR is a rapid, sensitive and useful method to detect fungal aetiology in microbial keratitis.

PCR-based diagnosis and quantification of mycotoxin-producing fungi

Mycotoxins are secondary metabolites produced by filamentous fungi which have toxicologically relevant effects on vertebrates if administered in small doses via a natural route. In order to improve food safety and to protect consumers from harmful contaminants, the presence of fungi with the potential to produce such compounds must be checked at critical control points during the production of agricultural commodities as well as during the process of food and feed preparation. Polymerase chain reaction (PCR)-based diagnosis has been applied as an alternative assay replacing cumbersome and time-consuming microbiological and chemical methods for the detection and identification of the most serious toxin producers in the fungal genera Fusarium, Aspergillus, and Penicillium. The current chapter covers the numerous PCR-based assays which have been published since the first description of the use of this technology to detect Aspergillus flavus biosynthesis genes in 1996.

Evaluation of polymerase chain reaction-based ribosomal DNA sequencing technique for the diagnosis of mycotic keratitis

PURPOSE

To evaluate the polymerase chain reaction (PCR) and sequencing-based ribosomal deoxyribonucleic acid (rDNA) typing technique for rapid and sensitive diagnosis of fungal keratitis.

DESIGN

Laboratory investigation.

METHODS

The present study included culture-based methods along with PCR and ITS2/5.8S rDNA sequencing to evaluate fungal infections in 32 corneal scrapings from patients with suspected mycotic keratitis.

RESULTS

Good correlation was found between the culture and PCR rDNA sequencing-based methods. We also identified fungal strains that were noncultivable in routine culture medium and fungal strains, which have been reported scarcely in previous reports from eastern Indian studies.

CONCLUSIONS

The PCR and rDNA sequencing-based approaches may be useful alternatives to culture-based techniques for the rapid and sensitive diagnosis of fungal keratitis. We found that clinically significant pathogenic fungal strains can be detected and differentiated by this method in a short period. This method therefore is useful for the early treatment of fungal infection.

Efficacy of Topical Caspofungin in Experimental Fusarium Keratitis

PURPOSE

To evaluate the efficacy of caspofungin in an experimental rabbit model of Fusarium keratitis and to compare it with amphotericin B.

METHODS

Eighteen New Zealand white rabbits were randomly divided into 2 treatment groups and 1 control group. One cornea of each rabbit was inoculated with Fusarium solani spores. The first group received topical amphotericin B 0.15%, the second group received topical caspofungin 1%, and the control group received topical balanced salt solution hourly for 2 days and then 4 times daily for 3 additional days. Treatment effects were evaluated by clinical assessment at days 3 and 5 and by fungal culture after 5 days of treatment.

RESULTS

In the treatment groups, progression of keratitis was inhibited, and cultures were sterile at the end of the study. In the control group, keratitis progressed, and cultures were positive for F. solani.

CONCLUSIONS

Topical caspofungin is effective in Fusarium keratitis, and clinical efficacy studies seem justified.

Structural differences between Fusarium strains investigated by FT-IR spectroscopy

The structural characteristics of Fusarium have received attention from both pure and applied scientists. Because many genes and physiological mechanisms are involved in the development of a particular structure type, this research is complicated. For revealing the structure of macromolecule in these fungal cells, FT-IR spectroscopy combined with multivariate statistical analysis was performed to characterize the structure of protein and polysaccharide of spores and mycelia obtained from different culture medium. The second derivative FT-IR spectra exhibited strain-specific infrared characteristics in the protein secondary structure sensitive amide I region. The region between 750 and 950 cm(-1) assigned to alpha- and beta-glucans was investigated for studied samples. Principal components analysis (PCA) allowed us to separate mycelia into two clusters according to different growth medium, indicating that spectra of strains may have been greatly affected by cultivation conditions.

Sensitive and rapid polymerase chain reaction based diagnosis of mycotic keratitis through single stranded conformation polymorphism

PURPOSE

To report a method for early and correct diagnosis of mycotic keratitis.

DESIGN

Clinical laboratory diagnostic study.

METHODS

Corneal scraping of all the four patients were processed for DNA extraction which were amplified by fungal specific primers of internal transcribed spacer region I (ITS1). These products were sequenced and analyzed by single stranded conformation polymorphism (SSCP) for species identification.

RESULTS

The DNA samples from corneal scrapings of all the four patients were successfully amplified by the primer pair ITS1 and ITS2 and similarity/dissimilarity were established by Jaccard's coefficient. Patient isolate 1 was identified as Nectria hematococca, isolate 2 as Candida albicans, and isolates 3 and 4 were identified as Bipolaris papendorfii. This led to prompt initiation of antifungal therapy in all the four cases where useful vision could be restored.

CONCLUSIONS

Early and correct diagnosis of mycotic keratitis by polymerase chain reaction could be obtained in all the four cases compared with conventional methods, which helped in the prompt initiation of antifungal therapy in patients.

Fungal keratitis

PURPOSE OF REVIEW

Throughout the world, fungal keratitis is a leading cause of ocular morbidity. The purpose of this review is to discuss the recently published literature in relation to the epidemiology, etiology, diagnosis, and therapy of fungal keratitis.

RECENT FINDINGS

Globally, the incidence of keratomycoses and systemic mycoses is rising. Current therapies are often ineffective. Ongoing research toward rapid diagnosis and specific drug therapy could minimize the morbidity caused by this preventable disease. New antifungal drugs, including voriconazole, have been applied recently for the treatment of keratomycosis.

SUMMARY

The incidence of fungal keratitis is on the rise in the densely populated continents of Asia and Africa. Filamentous fungi are the most frequently reported pathogens. Polyene antifungal antibiotics, the first-line therapy in fungal keratitis, are not effective in severe keratomycosis. Imidazole derivatives such as voriconazole and echinocandin may be the better choice in the future.

Fungal infections of the cornea

PURPOSE

To describe key aspects of fungal infections of the cornea, which constitute an important eye problem in outdoor workers in tropical and subtropical regions.

METHODS

Review of published studies and personal observations.

OBSERVATIONS

Fungal infections of the cornea are frequently caused by species of Fusarium, Aspergillus, Curvularia, and Candida. Trauma is the most important predisposing cause; ocular and systemic defects and prior application of corticosteroids are also important risk factors. Culture remains the cornerstone of diagnosis; direct microscopic detection of fungal structures in corneal scrapes or biopsies permits a rapid presumptive diagnosis. A variety of antifungals have been evaluated in therapy of this condition. Natamycin can only be given topically, while amphotericin B, miconazole, ketoconazole, itraconazole, and fluconazole can be administered by various routes. Topical amphotericin B (0.1-0.3%) is frequently the treatment of choice for infections due to Candida and related fungi, while topical natamycin (5%) is the choice for keratitis due to filamentous fungi. Medical therapy may fail, necessitating surgical intervention.

CONCLUSIONS

Fungal infections of the cornea continue to be an important cause of ocular morbidity, particularly in the agricultural communities of the developing world. A proper understanding of agent and host factors involved in these infections will improve the outcome of this condition.

Current perspectives on ophthalmic mycoses

Fungi may infect the cornea, orbit and other ocular structures. Species of Fusarium, Aspergillus, Candida, dematiaceous fungi, and Scedosporium predominate. Diagnosis is aided by recognition of typical clinical features and by direct microscopic detection of fungi in scrapes, biopsy specimens, and other samples. Culture confirms the diagnosis. Histopathological, immunohistochemical, or DNA-based tests may also be needed. Pathogenesis involves agent (invasiveness, toxigenicity) and host factors. Specific antifungal therapy is instituted as soon as the diagnosis is made. Amphotericin B by various routes is the mainstay of treatment for life-threatening and severe ophthalmic mycoses. Topical natamycin is usually the first choice for filamentous fungal keratitis, and topical amphotericin B is the first choice for yeast keratitis. Increasingly, the triazoles itraconazole and fluconazole are being evaluated as therapeutic options in ophthalmic mycoses. Medical therapy alone does not usually suffice for invasive fungal orbital infections, scleritis, and keratitis due to Fusarium spp., Lasiodiplodia theobromae, and Pythium insidiosum. Surgical debridement is essential in orbital infections, while various surgical procedures may be required for other infections not responding to medical therapy. Corticosteroids are contraindicated in most ophthalmic mycoses; therefore, other methods are being sought to control inflammatory tissue damage. Fungal infections following ophthalmic surgical procedures, in patients with AIDS, and due to use of various ocular biomaterials are unique subsets of ophthalmic mycoses. Future research needs to focus on the development of rapid, species-specific diagnostic aids, broad-spectrum fungicidal compounds that are active by various routes, and therapeutic modalities which curtail the harmful effects of fungus- and host tissue-derived factors.

Confocal microscopy of Aspergillus fumigatus keratitis

AIM

To use a confocal microscope to characterise the treated and untreated courses of fungal keratitis.

METHODS

In the first experiment, Aspergillus fumigatus stromal keratitis was produced in both eyes of seven New Zealand white rabbits. In the second experiment, keratitis was induced in right eyes of 20 rabbits. Group 1 rabbits were treated with topical fluconazole, group 2 rabbits received oral fluconazole, and group 3 rabbits were used as controls. The rabbits were examined with a slit lamp and confocal microscope 2, 6, 10, 14, and 20 days after inoculation. The corneal cultures were taken on days 2, 14, and 20 and biopsies were taken on days 2 and 22.

RESULTS

On days 14 and 22 confocal microscopy was more sensitive than culture technique in both treated and untreated animals, since not all cases of fungal keratitis can be cultured.

CONCLUSION

This study indicates that confocal microscopy is a rapid and sensitive diagnostic tool for both the early diagnosis and non-invasive follow up of fungal keratitis

Polymerase chain reaction based detection of fungi in infected corneas

AIMS

To evaluate a polymerase chain reaction (PCR) based assay to detect fungi in scrapings from infected corneas.

METHODS

A PCR assay was developed to amplify a portion of the fungal 18S ribosome gene. Corneal scrapings from 30 patients with presumed infectious keratitis were evaluated using this assay, as well as by standard microbiological techniques, and the results were compared. Conjunctival swabs from each patient's healthy, fellow eye were also evaluated by PCR.

RESULTS

PCR and fungal culture results matched (were both positive or both negative for fungi) in 22 (74%) of 30 scrapings from infected corneas. Three (10%) of 30 samples were PCR positive but fungal culture negative; two of these appeared clinically to represent fungal infections, and the third was clinically indeterminate. Four (13%) scrapings were positive by PCR but also by bacterial and not fungal culture. One specimen (3%) was PCR negative but fungal culture positive. Of the conjunctival swabs from each patient's healthy fellow eye, five (17%) of 30 were positive by PCR, and the opposite, infected eye of all five of these harboured a fungal infection.

CONCLUSIONS

PCR is promising as a means to diagnose fungal keratitis and offers some advantages over culture methods, including rapid analysis and the ability to analyse specimens far from where they are collected.

Polymerase chain reaction diagnosis in fungal keratitis caused by Alternaria alternata

PURPOSE

To contribute toward assessing the effectiveness of polymerase chain reaction as a rapid method in diagnosis of torpid keratitis caused by opportunistic fungi.

METHODS

Interventional case report. A 50-year-old man with a corneal abscess in the right eye treated for a period of 6 months with different combinations of broad-spectrum antibiotics and steroids was referred to our center. Corneal scraping was taken for microbiological study, including classic cultures and polymerase chain reaction. Amplified DNA was sequenced to identify the pathogen.

RESULTS

Polymerase chain reaction amplification was negative for Acanthamoeba species and positive for fungi. The sequence analysis showed Alternaria alternata as the causal agent in 24 hours. Cultures confirmed the identification in 10 days.

CONCLUSION

Polymerase chain reaction amplification with subsequent DNA-typing was revealed to be a useful method for detection of ocular pathogens such as A. alternata involved in cases of torpid keratitis, even in the presence of broad-spectrum antimicrobial therapy.

Detection and identification of fungal pathogens by PCR and by ITS2 and 5.8S ribosomal DNA typing in ocular infections

The goal of this study was to determine whether sequence analysis of internal transcribed spacer/5.8S ribosomal DNA (rDNA) can be used to detect fungal pathogens in patients with ocular infections (endophthalmitis and keratitis). Internal transcribed spacer 1 (ITS1) and ITS2 and 5.8S rDNA were amplified by PCR and seminested PCR to detect fungal DNA. Fifty strains of 12 fungal species (yeasts and molds) were used to test the selected primers and conditions of the PCR. PCR and seminested PCR of this region were carried out to evaluate the sensitivity and specificity of the method. It proved possible to amplify the ITS2/5.8S region of all the fungal strains by this PCR method. All negative controls (human and bacterial DNA) were PCR negative. The sensitivity of the seminested PCR amplification reaction by DNA dilutions was 1 organism per PCR, and the sensitivity by cell dilutions was fewer than 10 organisms per PCR. Intraocular sampling or corneal scraping was undertaken for all patients with suspected infectious endophthalmitis or keratitis (nonherpetic), respectively, between November 1999 and February 2001. PCRs were subsequently performed with 11 ocular samples. The amplified DNA was sequenced, and aligned against sequences in GenBank at the National Institutes of Health. The results were PCR positive for fungal primers for three corneal scrapings, one aqueous sample, and one vitreous sample; one of them was negative by culture. Molecular fungal identification was successful in all cases. Bacterial detection by PCR was positive for three aqueous samples and one vitreous sample; one of these was negative by culture. Amplification of ITS2/5.8S rDNA and molecular typing shows potential as a rapid technique for identifying fungi in ocular samples.