Comparison of axenic and monoxenic media for isolation of Acanthamoeba

Epidemiology of and Genetic Factors Associated with Acanthamoeba Keratitis

Acanthamoeba keratitis (AK) is a severe, rare protozoal infection of the cornea. Acanthamoeba can survive in diverse habitats and at extreme temperatures. AK is mostly seen in contact lens wearers whose lenses have become contaminated or who have a history of water exposure, and in those without contact lens wear who have experienced recent eye trauma involving contaminated soil or water. Infection usually results in severe eye pain, photophobia, inflammation, and corneal epithelial defects. The pathophysiology of this infection is multifactorial, including the production of cytotoxic proteases by Acanthamoeba that degrades the corneal epithelial basement membrane and induces the death of ocular surface cells, resulting in degradation of the collagen-rich corneal stroma. AK can be prevented by avoiding risk factors, which includes avoiding water contact, such as swimming or showering in contact lenses, and wearing protective goggles when working on the land. AK is mostly treated with an antimicrobial therapy of biguanides alone or in combination with diaminidines, although the commercial availability of these medicines is variable. Other than anti-amoeba therapies, targeting host immune pathways in Acanthamoeba disease may lead to the development of vaccines or antibody therapeutics which could transform the management of AK.

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.

Intracellular Microbiome Profiling of the Acanthamoeba Clinical Isolates from Lens Associated Keratitis

Acanthamoeba act as hosts for various microorganisms and pathogens, causing Acanthamoeba Keratitis (AK). To investigate the association between endosymbionts and AK progression, we performed a metagenomics study to characterize the intracellular microbiome from five lenses associated with AK isolates and standard strains to characterize the role of ocular flora in AK progression. The used clinical isolates were axenic cultured from lenses associated with AK patients. AK isolates and standard controls such as 16S ribosomal RNA sequencing techniques were used for analysis. The microbiome compositions and relative abundance values were compared. The orders of Clostridiales and Bacteroidales presented major populations of intracellular microbes belonging to all isolates. Comparison of the different source isolates showed that most of the abundance in keratitis isolates came from Ruminococcus gnavus (121.0 folds), Eubacterium dolichum (54.15 folds), Roseburia faecis (24.51 folds), and Blautia producta (3.15 folds). Further analysis of the relative abundance data from keratitis isolates showed that Blautia producta was positively correlated with the disease course. In contrast, Bacteroides ovatus was found to be abundant in early-stage keratitis isolates. This study reveals the abundant anaerobic Gram-positive rods present in severe keratitis isolate and characterize the association between Acanthamoeba and ocular flora in AK progression.

Development of an immunochromatographic assay kit using fluorescent silica nanoparticles for rapid diagnosis of Acanthamoeba keratitis

We developed an immunochromatographic assay kit that uses fluorescent silica nanoparticles bound to anti-Acanthamoeba antibodies (fluorescent immunochromatographic assay [FICGA]) and evaluated its efficacy for the detection of Acanthamoeba and diagnosis of Acanthamoeba keratitis (AK). The sensitivity of the FICGA kit was evaluated using samples of Acanthamoeba trophozoites and cysts diluted to various concentrations. A conventional immunochromatographic assay kit with latex labels (LICGA) was also evaluated to determine its sensitivity in detecting Acanthamoeba trophozoites. To check for cross-reactivity, the FICGA was performed by using samples of other common causative pathogens of infectious keratitis, such as Pseudomonas aeruginosa, Staphylococcus aureus, Staphylococcus epidermidis, and Candida albicans. Corneal scrapings from patients with suspected AK were tested with the FICGA kit to detect the presence of Acanthamoeba, and the results were compared with those of real-time PCR. The FICGA kit detected organisms at concentrations as low as 5 trophozoites or 40 cysts per sample. There were no cross-reactivities with other pathogens. The FICGA was approximately 20 times more sensitive than the LICGA for the detection of Acanthamoeba trophozoites. The FICGA kit yielded positive results for all 10 patients, which corresponded well with the real-time PCR results. The FICGA kit demonstrated high sensitivity for the detection of Acanthamoeba and may be useful for the diagnosis of AK.

A highly sensitive method for molecular diagnosis of fungal keratitis: a dot hybridization assay

PURPOSE

Fungal keratitis (FK) is an important cause of ocular morbidity, especially for people living in the agricultural communities of the developing world. Current diagnostic methods may lack sensitivity (direct microscopy) or are time consuming (culture). The aim of this study was to develop a dot hybridization assay for sensitive and rapid diagnosis of FK.

DESIGN

Evaluation of diagnostic test or technology.

PARTICIPANTS AND CONTROLS

Fifty corneal scrapes (49 patients) from consecutive cases of clinically suspected microbial keratitis were analyzed prospectively.

METHODS

Molecular detection of fungi in the scrapes was performed by amplification of the internal transcribed spacer region (ITS) that contained the target gene (5.8S rRNA gene) by polymerase chain reaction (PCR), followed by hybridization of the PCR product to a fungus-specific oligonucleotide probe immobilized on a nylon membrane. The results were compared with those obtained by gram-stain microscopy, culture, and gel electrophoresis of the PCR products. Discrepant results were resolved by cloning and resequencing of the amplified ITS fragments.

MAIN OUTCOME MEASURES

Performance of the dot hybridization assay, including sensitivity, specificity, and positive and negative predictive values, was evaluated.

RESULTS

Ten scrapes demonstrated positive results by both the dot hybridization assay and culture. However, 11 scrapes demonstrated positive results by the dot hybridization assay, but demonstrated negative results by culture, and 10 of the 11 samples were considered to be positive for FK by cloning and resequencing of the amplified ITS fragment and by a pathologic examination or clinical course review. The sensitivities for diagnosis of FK by the dot hybridization assay and culture were 100% and 50%, respectively, whereas the specificities were 96.7% and 100%, respectively.

CONCLUSIONS

The dot hybridization assay is a highly sensitive and specific diagnostic tool for FK. The method provides a much higher sensitivity than that of culture (100% vs. 50%; P<0.001). The hybridization procedure can be finished within a working day. It is expected that the method can have an impact on the diagnosis and treatment of FK in the future.

FINANCIAL DISCLOSURE(S)

The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Microsporidia and Acanthamoeba: the role of emerging corneal pathogens

Parasitic organisms are increasingly recognized as human corneal pathogens. A notable increase in both well-defined Acanthamoeba keratitis and a more dramatic increase in reported cases of Microsporidia keratitis have suggested significant outbreaks of parasitic keratitis around the world. Historical and contemporary baselines as well as a familiar associated clinical presentation reinforce the significant outbreak of Acanthamoeba keratitis in the United States. The remarkable rise in cases of Microsporidia keratitis, however, lacks these established baselines and, further, describes a disease that is inconsistent with previous definitions of disease. While a well-defined, abrupt increase strongly suggests temporally related risk factors, most likely environmental, involved in the Acanthamoeba outbreak, the rise in Microsporidia keratitis suggests that increased awareness and improved diagnostic acumen are a significant factor in case ascertainment. Regardless, recent evidence indicates that both parasitic diseases are likely underreported in various forms of infectious keratitis, which may have unrecognized but significant implications in the pathogenesis of both primary protozoal and polymicrobial keratitis. Further understanding of the incidence and interaction of these organisms with current therapeutic regimens and more commonly recognized pathogens should significantly improve diagnosis and alter clinical outcomes.

Acanthamoeba castellanii: in vitro UAH-T17c3 trophozoite growth study in different culture media

Acanthamoeba is one of the most common free-living amoebae. It is widespread in the environment and can infect humans, causing diseases such as keratitis and encephalitis. In this study, we used a strain of Acanthamoeba castellanii (UAH-T17c3) isolated from cooling towers, and we evaluated the efficiency of three different culture media in its growth, with the aim of selecting one which allowed better growth, was easier to prepare, and was able to keep the trophozoites by long periods of time. We compared the growth of A. castellanii in peptone-yeast extract-glucose (PYG, the most commonly used medium to grow this strain) to the growth in PYG-Bactocasitone (PYG with 2% Bactocasitone) and brain-heart infusion broth (BHI is a standard microbiological medium rarely used in the culture of amoebae). Flow cytometry and cell count results showed all three media allowed the growth of trophozoites. PYG-Bactocasitone was shown to be the best for long-term culture. The BHI and PYG-Bactocasitone media have not been used for Acanthamoeba spp. trophozoite growth. In view of the results, we can affirm that these media are adequate to grow the above-mentioned strain for in vitro screening assays.

Potentially pathogenic acanthamoeba isolated from a hospital in Brazil

Studies on free-living amoebae (FLA), has been increased in recent years, especially related to the genus Acanthamoeba, because these organisms are widely found in the environment. The present work isolated and characterized this organism from biofilms and dust in hospital environment. 135 samples were collected in 15 different environments in a hospital at the south of Brazil. Thirty-one (23%) isolates were identified as morphologically belonging to the Acanthamoeba genus and 10 of these were submitted to temperature and osmotolerance tests as criterion for evaluation of the viability and pathogenicity. The tests indicate that four (40%) of these isolates could be potentially pathogenic because grew at high temperature (40 degrees C) and osmolarity (mannitol 1 M). Some isolates genotypes were determined after ribosomal DNA sequencing. These data revealed that three dust isolates belong to T4, two biofilm isolates to T5 and one dust isolate to T3 genotype. Therefore, Acanthamoeba found in the hospital environment represents a risk for people that circulate there.

Laboratory diagnosis of amoebic keratitis: comparison of four diagnostic methods for different types of clinical specimens

Amoebic keratitis causes significant ocular morbidity in contact lens wearers. Current diagnostic methods for amoebic keratitis are insensitive and labor-intensive and have poor turnaround time. We evaluated four laboratory methods for detection of acanthamoebae in clinical specimens. Deidentified, delinked consecutive specimens from patients with suspected amoebic keratitis were assayed for acanthamoebae by direct smear analysis, culture, and PCR using two different primer sets specific for Acanthamoeba ribosomal DNA. The consensus reference standard was considered fulfilled when the results for any two of the four tests were positive, and the outcome measures were sensitivity and specificity. Of 107 specimens assayed over an 18-month period, 20 were positive for acanthamoebae. The sensitivity and specificity of each assay were as follows, respectively: for smear analysis, 55% (95% confidence interval [CI], 33.2 to 76.8%) and 100%; for culture, 73.7% (95% CI, 54.4 to 93.0%) and 100%; for PCR using Nelson primers, 90% (95% CI, 76.9 to 100%) and 90.8% (95% CI, 84.7 to 96.9%); and for PCR using JDP primers, 65% (95% CI, 44.1 to 85.9%) and 100%. Nelson primer PCR demonstrated a single-organism level of analytic sensitivity. The performance characteristics of the assays varied by specimen type, with contact lenses and casings showing the highest rates of detectable acanthamoebae and the highest diagnostic sensitivities for direct smear analysis, culture, and JDP primer PCR, though these results are based on small numbers and should be interpreted cautiously. These findings have important implications for clinicians collecting diagnostic specimens and for diagnostic laboratories, especially in outbreak situations.

[Keratitis due to Acanthamoeba]

Free-living amebae appertaining to the genus Acanthamoeba, Naegleria and Balamuthia are the most prevalent protozoa found in the environment. These amebae have a cosmopolitan distribution in soil, air and water, providing multiple opportunities for contacts with humans and animals, although they only occasionally cause disease. Acanthamoeba spp. are the causative agent of granulomatous amebic encephalitis, a rare and often fatal disease of the central nervous system, and amebic keratitis, a painful disease of the eyes. Keratitis usually follows a chronic course due to the delay in diagnosis and subsequent treatment. The clear increase in Acanthamoeba keratitis in the last 20 years is related to the use and deficient maintenance of contact lenses, and to swimming while wearing them. The expected incidence is one case per 30,000 contact lens wearers per year, with 88% of cases occurring in persons wearing hydrogel lenses. This review presents information on the morphology, life-cycle and epidemiology of Acanthamoeba, as well as on diagnostic procedures (culture), appropriate antimicrobial therapy, and prevention measures.

Microorganisms resistant to free-living amoebae

Free-living amoebae feed on bacteria, fungi, and algae. However, some microorganisms have evolved to become resistant to these protists. These amoeba-resistant microorganisms include established pathogens, such as Cryptococcus neoformans, Legionella spp., Chlamydophila pneumoniae, Mycobacterium avium, Listeria monocytogenes, Pseudomonas aeruginosa, and Francisella tularensis, and emerging pathogens, such as Bosea spp., Simkania negevensis, Parachlamydia acanthamoebae, and Legionella-like amoebal pathogens. Some of these amoeba-resistant bacteria (ARB) are lytic for their amoebal host, while others are considered endosymbionts, since a stable host-parasite ratio is maintained. Free-living amoebae represent an important reservoir of ARB and may, while encysted, protect the internalized bacteria from chlorine and other biocides. Free-living amoebae may act as a Trojan horse, bringing hidden ARB within the human "Troy," and may produce vesicles filled with ARB, increasing their transmission potential. Free-living amoebae may also play a role in the selection of virulence traits and in adaptation to survival in macrophages. Thus, intra-amoebal growth was found to enhance virulence, and similar mechanisms seem to be implicated in the survival of ARB in response to both amoebae and macrophages. Moreover, free-living amoebae represent a useful tool for the culture of some intracellular bacteria and new bacterial species that might be potential emerging pathogens.

Acanthamoeba spp. as agents of disease in humans

Acanthamoeba spp. are free-living amebae that inhabit a variety of air, soil, and water environments. However, these amebae can also act as opportunistic as well as nonopportunistic pathogens. They are the causative agents of granulomatous amebic encephalitis and amebic keratitis and have been associated with cutaneous lesions and sinusitis. Immuno compromised individuals, including AIDS patients, are particularly susceptible to infections with Acanthamoeba. The immune defense mechanisms that operate against Acanthamoeba have not been well characterized, but it has been proposed that both innate and acquired immunity play a role. The ameba's life cycle includes an active feeding trophozoite stage and a dormant cyst stage. Trophozoites feed on bacteria, yeast, and algae. However, both trophozoites and cysts can retain viable bacteria and may serve as reservoirs for bacteria with human pathogenic potential. Diagnosis of infection includes direct microscopy of wet mounts of cerebrospinal fluid or stained smears of cerebrospinal fluid sediment, light or electron microscopy of tissues, in vitro cultivation of Acanthamoeba, and histological assessment of frozen or paraffin-embedded sections of brain or cutaneous lesion biopsy material. Immunocytochemistry, chemifluorescent dye staining, PCR, and analysis of DNA sequence variation also have been employed for laboratory diagnosis. Treatment of Acanthamoeba infections has met with mixed results. However, chlorhexidine gluconate, alone or in combination with propamidene isethionate, is effective in some patients. Furthermore, effective treatment is complicated since patients may present with underlying disease and Acanthamoeba infection may not be recognized. Since an increase in the number of cases of Acanthamoeba infections has occurred worldwide, these protozoa have become increasingly important as agents of human disease.

Laboratory diagnosis of Acanthamoeba keratitis using buffered charcoal-yeast extract agar

PURPOSE

To evaluate the use of buffered charcoal-yeast extract agar for the isolation of Acanthamoeba from clinical specimens.

METHODS

We retrospectively reviewed laboratory records of patients with ocular acanthamebic infection from October 1993 to September 1997 to compare the recovery of Acanthamoeba from clinical specimens inoculated onto various media. We then compared the experimental recovery of 10 corneal isolates of Acanthamoeba on buffered charcoal-yeast extract and blood agars.

RESULTS

Paired data for buffered charcoal-yeast extract and blood agars were available from 24 cultures performed in 13 cases of ocular acanthamebic infection. Acanthamebic trails were detected on both buffered charcoal-yeast extract and blood agars in nine cultures, only on buffered charcoal-yeast extract agar in nine cultures, and only on blood agar in one culture (P = .027). In the experimental study, all 10 clinical isolates produced trails on buffered charcoal-yeast extract agar, and the mean recovery after 10 days of incubation ranged from 38% to 95% of the original inoculum number. For seven of the 10 isolates, more than 70% of the original inoculum was recovered on buffered charcoal-yeast extract agar. Only two of the 10 strains produced persistent trails on the blood agar, and the mean recoveries after 10 days of incubation were 0.67% and 1.17%. Recovery was significantly better on buffered charcoal-yeast extract agar than blood agar (P < or = .0003).

CONCLUSION

Buffered charcoal-yeast extract agar is an excellent commercially available culture medium for the recovery of Acanthamoeba.