Development, Optimization, and Validation of a Multiplex Real-Time PCR Assay on the BD MAX Platform for Routine Diagnosis of Acanthamoeba Keratitis

An International External Quality Assessment Scheme to Assess the Diagnostic Performance of Polymerase Chain Reaction Detection of Acanthamoeba Keratitis

PURPOSE

The purpose of this study was to assess the variation in methods and to determine whether an External Quality Assessment Scheme (EQAS) for polymerase chain reaction (PCR) detection of Acanthamoeba keratitis is valuable for the diagnostic process.

METHODS

A multicenter EQAS was introduced, covering 16 diagnostic laboratories. Using Acanthamoeba castellanii ATCC strain 30010, 3 sets of samples were prepared, containing different amounts of DNA, cysts, or trophozoites. Samples were masked and sent to the participants with instructions for use and a questionnaire concerning the applied methodologies. Special attention in this questionnaire was given to the used pretreatment methods to assess existing variations in these procedures.

RESULTS

A large variation in the methodologies and substantial differences in the diagnostic performance were found between participants. In contrast to the DNA samples where all participants had a perfect score, several false negative results were reported for the samples containing cysts or trophozoites. Only 9 participants had an optimal score, whereas one participant reported all samples as negative, one participant reported failures due to inhibition, and the other 5 reported in total 7 false negative results. A clear correlation was noticed between the PCR detection rate and the number of cysts or trophozoites in the sample.

CONCLUSIONS

The results indicate that a pretreatment procedure can be a risky step in PCR-based detections of Acanthamoeba , but it improves the sensitivity and reliability, especially of samples containing cysts. Therefore, participation in an EQAS is informative for routine diagnostic laboratories and can assist in improving the laboratory procedures used for the diagnosis of Acanthamoeba keratitis.

Acanthamoeba keratitis: Experience from a tertiary eye care center in North India

The free-living amebae of genus Acanthamoeba are an important cause of microbial keratitis. The clinical appearance of Acanthamoeba keratitis (AK) usually mimics viral or fungal keratitis. Thus, microbiological workup plays a significant role in the diagnosis and timely treatment of such cases. We report a retrospective case series of seven culture-confirmed AK cases from a tertiary eye care center in North India. Various risk factors and triggers of infection, clinical presentations, microbiological findings, and management of AK are elucidated.

Microbiological diagnosis of Acanthamoebic keratitis: experience from tertiary care center of North India

Acanthamoeba keratitis (AK) is a painful vision-threatening infection caused by pathogenic free-living Acanthamoeba. Due to the non-specific clinical presentation, this condition tends to be misdiagnosed by clinicians. A timely diagnosis is crucial for favorable visual outcome. Three hundred patients with suspected microbial keratitis presenting to the Advanced Eye Center at our tertiary care center in North India during the period from 2014 to 2018 were included. Patient's corneal scrapings, contact lens, lens solution, lens case, and tears were processed for microscopic examination by Giemsa and Calcofluor staining, non-nutrient agar (NNA) culture and molecular diagnosis by conventional PCR (cPCR) and Real-time PCR (qPCR). 18S rDNA gene sequencing was done to assess phylogenetic relationship. AK was found in 3.6% (11/300) of non-bacterial non-fungal keratitis patients. Among microbiological techniques, microscopy for Acanthamoeba was positive in 7 cases, NNA culture was positive in 9 cases and 11 cases were detected both by cPCR and qPCR. The sensitivity of microscopy, culture, cPCR and qPCR was 63.64%, 81.82 %, 100%, and 100% respectively whereas specificity was 100% for all the tests. 18S rDNA sequencing revealed that A. castellanii was the predominant species and isolates were genetically distinct. AK should be considered in the differential diagnosis of infectious keratitis. Molecular tests are useful for rapid, sensitive and specific diagnosis and must be included in workup of keratitis.