Rapid detection and simultaneous molecular profile characterization of Acanthamoeba infections

PCR and culture for diagnosis of Acanthamoeba keratitis

Background/Aims

Acanthamoeba keratitis (AK) is a rare but sight-threatening infection. Molecular diagnosis of corneal scraping has improved the diagnosis of AK. Different molecular targets and conditions have been used in diagnosis thus far. In this study, we prospectively compared the performance of five PCR assays on corneal samples for the diagnosis of AK.

Methods

1217 corneal scraping samples were obtained from patients, for whom an AK was suspected. Sample processing involved both molecular diagnostics and culture. Acanthamoeba PCR assays detected different regions of the Acanthamoeba nuclear small-subunit rRNA gene: three final point PCR assays using Nelson, ACARNA and JDP1–JDP2 pairs of primers, and two real-time PCR assays using Acant primer-probe. Human DNA and internal control were co-amplified in the real-time PCR assay to ensure scraping quality and the absence of inhibitors. In the absence of a gold standard, the performance of each test was evaluated using latent class analysis. Genotypes of Acanthamoeba isolates were also characterised.

Results

Estimated prevalence of AK was 1.32%. The sensitivity of Acanthamoeba diagnostic PCRs (73.3% to 86.7%) did not differ significantly from that of culture (66.7%), or according to the target sequence or the technology. Sensitivity could be increased to 93.8% or 100% by combining two or three assays, respectively. PCR specificity (99.3% to 100%) differed between the assays. T4 was the predominant Acanthamoeba genotype (84.6%).

Conclusions

Culture and a single PCR assay could lead to misdiagnosing AK. A combination of different PCR assays and improved sample quality could increase diagnosis sensitivity.

Acanthamoeba Keratitis: Current Status and Urgent Research Priorities

Background:

First discovered in the early 1970s, Acanthamoeba keratitis has remained a major eye infection and presents a significant threat to the public health, especially in developing countries. The aim is to present a timely review of our current understanding of the advances made in this field in a comprehensible manner and includes novel concepts and provides clear directions for immediate research priorities.

Methods:

We undertook a search of bibliographic databases for peer-reviewed research literature and also summarized our published results in this field.

Results:

The present review focuses on novel diagnostic and therapeutic strategies in details which can provide access to management and treatment of Acanthamoeba keratitis. This coupled with the recently available genome sequence information together with high throughput genomics technology and innovative approaches should stimulate interest in the rational design of preventative and therapeutic measures. Current treatment of Acanthamoeba keratitis is problematic and often leads to infection recurrence. Better understanding of diagnosis, pathogenesis, pathophysiology and therapeutic regimens, would lead to novel strategies in treatment and prophylaxis.

Assessment of Confocal Microscopy for the Diagnosis of Polymerase Chain Reaction-Positive Acanthamoeba Keratitis: A Case-Control Study

PURPOSE

To determine in vivo confocal microscopy diagnostic criteria to diagnose Acanthamoeba keratitis (AK) using polymerase chain reaction (PCR) as the reference diagnostic technique.

DESIGN

Retrospective case-control study. Data were recorded prospectively and analyzed retrospectively.

PARTICIPANTS

Fifty patients with PCR-positive AK (study group) and 50 patients with bacterial, fungal, viral, or immune keratitis featuring negative Acanthamoeba PCR results (control group).

METHODS

In vivo confocal microscopy performed at the acute stage of keratitis.

MAIN OUTCOME MEASURES

Presence of in vivo confocal microscopy images suggestive of AK. Multivariate logistic regression was used to determine the relationship between types of images and presence of PCR-positive AK.

RESULTS

The following 4 types of images were associated significantly with PCR-positive AK (P < 0.05): bright spots (round or ovoid hyperreflective objects with no double wall; diameter, <30 μm); target images (hyperreflective objects with hyporeflective halo; diameter, <30 μm); clusters of hyperreflective objects (diameter, <30 μm); and trophozoite-like objects (diameter, >30 μm). Specificity of both target and trophozoite images was 100%. This figure was 98.2% for clusters and 48.2% for bright spots. If the diagnosis of AK was made on presence of target images, clusters or trophozoite images (at least 1 of the 3 features), the positive predictive value of confocal microscopy was 87.5% and the negative predictive value was 58.5%.

CONCLUSIONS

Acanthamoeba keratitis is a serious vision-threatening disease. In vivo confocal microscopy can help in this challenging diagnosis, especially when PCR is delayed, shows negative results, or is not available. Target images and trophozoite-like images are pathognomonic of AK. Clusters of hyperreflective objects are highly specific of AK. However, the overall sensitivity of in vivo confocal microscopy features of AK is low. In addition to the clinical features, microbiological tests (direct examination and cultures of corneal scrapings), and PCR, in vivo confocal microscopy allows for more rapid diagnosis and treatment initiation, potentially leading to an improved outcome.

Genotypic, physiological, and biochemical characterization of potentially pathogenic Acanthamoeba isolated from the environment in Cairo, Egypt

Acanthamoebae are the most common opportunistic amphizoic protozoa that cause life-threatening granulomatous amoebic encephalitis in immunocompromised individuals and sight-threatening amoebic keratitis (AK) in contact lens wearers. The present work aimed to determine the presence of Acanthamoeba isolates in different environmental sources: water, soil, and dust in Cairo, Egypt and to characterize the pathogenic potential of the isolated Acanthamoeba using physiological and biochemical assays as well as determination of the genotypes in an attempt to correlate pathogenicity with certain genotypes. The study included the collection of 22 corneal scrapings from patients complaining of symptoms and signs indicative of acanthamoeba keratitis (AK) and 75 environmental samples followed by cultivation on non-nutrient agar plates preseeded with E. coli. Positive samples for Acanthamoeba were subjected to osmo- and thermo-tolerance assays and zymography analysis. Potentially pathogenic isolates were subjected to PCR amplification using genus-specific primer pair. Isolates were classified at the genotype level based on the sequence analysis of Acanthamoeba 18S rRNA gene (diagnostic fragment 3). The total detection rate for Acanthamoeba in environmental samples was 33.3 %, 31.4 % in water, 40 % in soil, and 20 % in dust samples. Three and two Acanthamoeba isolates from water and soil sources, respectively, had the potential for pathogenicity as they exhibited full range of pathogenic traits. Other 12 isolates were designated as weak potential pathogens. Only ten of the environmental isolates were positive in PCR and were classified by genotype analysis into T4 genotype (70 %), T3 (10 %) and T5 (20 %). Potential pathogens belonged to genotypes T4 (from water) and T5 (from soil) while weak potential pathogens belonged to genotypes T3 (from water) and T4 (from water and soil). Additionally, T7 genotype was isolated from keratitis patients. There is a considerable variation in the response of Acanthamoeba members of the same genotype to pathogenicity indicator assays making correlation of pathogenicity with certain genotypes difficult. Presence of potentially pathogenic Acanthamoeba isolates in habitats related directly to human populations represent a risk for human health. Isolation of Acanthamoeba genotype T7 from AK cases, which is commonly considered as nonpathogenic, might draw the attention to other Acanthamoeba genotypes considered as non pathogenic and reevaluate their role in production of human infections. To our knowledge, this is the first study on the presence and distribution of Acanthamoeba genotypes in the environment, Cairo, Egypt.

How to use... eye swabs

Conjunctivitis is a very common presentation to general practitioners and general paediatricians. The investigation of conjunctivitis can be a significant cost to microbiology laboratories due to the high volume of samples that can be submitted, particularly from patients in the community. The key issue is to send eye swabs in clinical situations where it can make a difference to management, and limiting the use of eye swabs in routine cases of conjunctivitis which are likely to be due to viruses. For investigation of neonatal conjunctivitis we recommend sending a bacterial swab for routine culture, and also a swab for molecular detection of Chlamydia trachomatis and Neisseria gonorrhoeae. In older children with mild conjunctivitis no swab is necessary unless there is marked conjunctival injection. In this article we also highlight patient populations that require specialist tests to be sent as part of their assessment such as contact lens wearers and sexually active teenagers.

Genotypic characterization of amoeba isolated from Acanthamoeba keratitis in Poland

Free-living amoebae belonging to the genus Acanthamoeba are the causative factor of many diseases. Among others, they cause Acanthamoeba keratitis (AK), a condition that usually occurs in contact lens wearers, though it is also observed in non-wearers. The number of diagnosed cases of AK increased more than eightfold during 8 years in the USA, and a proportional increase in frequency also occurred in Poland and Europe. Cases of AK are usually diagnosed late, and their therapy is difficult and rarely successful. AK is an uncommon diagnosis in Poland. The increased number of positive cases observed in our laboratory may reflect the growing at-risk population of contact lens wearers. Acanthamoeba as a genus of facultative human parasites is currently classified into 17 genotypes. Isolates belonging to seven genotypes were found to be associated with AK. One genotype in particular, T4, was found to be overrepresented in human disease. The main finding of our study is that in Poland, AK is almost always associated with the T4 genotype.

Imaging angiogenesis, inflammation, and metastasis in the tumor microenvironment with magnetic resonance imaging

With the development of new imaging techniques, the potential for probing the molecular, cellular, and structural components of the tumor microenvironment in situ has increased dramatically. A multitude of imaging modalities have been successfully employed to probe different aspects of the tumor microenvironment, including expression of molecules, cell motion, cellularity, vessel permeability, vascular perfusion, metabolic and physiological changes, apoptosis, and inflammation. This chapter focuses on the most recent advances in magnetic resonance imaging methods, which offer a number of advantages over other methodologies, including high spatial resolution and the use of nonionizing radiation, as well as the use of such methods in the context of primary and secondary brain tumors. It also highlights how they can be used to assess the molecular and cellular changes in the tumor microenvironment in response to therapy.

Detection of microorganisms in granulomas that have been formalin-fixed: review of the literature regarding use of molecular methods

Granuloma is an organized aggregate of immune cells that under the microscope appear as epithelioid macrophages. A granuloma can only be diagnosed when a pathologist observes this type of inflammation under the microscope. If a foreign body or a parasite is not observed inside the granuloma, stains for acid-fast bacilli and fungi are ordered since mycobacteria and fungi are frequently the cause of this type of inflammation. It is calculated that 12 to 36% of granulomas do not have a specific etiology and many have wondered if with new molecular methods we could reduce this number. This paper will summarize the frequently known causes of granulomas and will present the recent literature regarding the use of molecular techniques on tissue specimens and how these have helped in defining causative agents. We will also briefly describe new research regarding formation and function of granulomas and how this impacts our ability to find an etiologic agent.