Evaluation of loop-mediated isothermal amplification assay for rapid diagnosis of Acanthamoeba keratitis

Acanthamoeba keratitis - A review

This is a comprehensive review after a thorough literature search in PubMed-indexed journals, incorporating current information on the pathophysiology, clinical features, diagnosis, medical and surgical therapy, as well as outcomes of Acanthamoeba keratitis (AK). AK is a significant cause of ocular morbidity, and early diagnosis with timely institution of appropriate therapy is the key to obtaining good outcomes. The varied presentations result in frequent misdiagnosis, and co-infections can increase the morbidity of the disease. The first line of therapy continues to be biguanides and diamidines, with surgery as a last resort.

Ultrasensitive and rapid diagnostic tool for detection of Acanthamoeba castellanii

Acanthamoeba keratitis is a devastating infectious disease of the cornea caused by an opportunistic amoeba, Acanthamoeba castellanii. It is poorly recognized, and diagnostic delays can lead to irreversible damage to the vision. The gold standard for diagnosis has been a sample culture that lasts approximately 2 weeks. Nevertheless, the essence of time has led to the need for an accurate and fast technique to detect A. castellanii from a sample. We developed both traditional and quantitative real-time-PCR-based methods to detect A. castellanii in less than 3 hours and with the sensitivity of one amoeba. Diagnostic laboratories can select the best-suited method for their purposes from 2 comparable methods. The correct treatment can be initiated from the emergency room when the diagnosis has been made quickly within a few hours, hence saving the patient from long-term complications.

Diagnosis of Acanthamoeba Keratitis: Past, Present and Future

Acanthamoeba keratitis (AK) is a painful and sight-threatening parasitic corneal infection. In recent years, the incidence of AK has increased. Timely and accurate diagnosis is crucial during the management of AK, as delayed diagnosis often results in poor clinical outcomes. Currently, AK diagnosis is primarily achieved through a combination of clinical suspicion, microbiological investigations and corneal imaging. Historically, corneal scraping for microbiological culture has been considered to be the gold standard. Despite its technical ease, accessibility and cost-effectiveness, the long diagnostic turnaround time and variably low sensitivity of microbiological culture limit its use as a sole diagnostic test for AK in clinical practice. In this review, we aim to provide a comprehensive overview of the diagnostic modalities that are currently used to diagnose AK, including microscopy with staining, culture, corneal biopsy, in vivo confocal microscopy, polymerase chain reaction and anterior segment optical coherence tomography. We also highlight emerging techniques, such as next-generation sequencing and artificial intelligence-assisted models, which have the potential to transform the diagnostic landscape of AK.

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.

Diagnostic armamentarium of infectious keratitis: A comprehensive review

Infectious keratitis (IK) represents the leading cause of corneal blindness worldwide, particularly in developing countries. A good outcome of IK is contingent upon timely and accurate diagnosis followed by appropriate interventions. Currently, IK is primarily diagnosed on clinical grounds supplemented by microbiological investigations such as microscopic examination with stains, and culture and sensitivity testing. Although this is the most widely accepted practice adopted in most regions, such an approach is challenged by several factors, including indistinguishable clinical features shared among different causative organisms, polymicrobial infection, long diagnostic turnaround time, and variably low culture positivity rate. In this review, we aim to provide a comprehensive overview of the current diagnostic armamentarium of IK, encompassing conventional microbiological investigations, molecular diagnostics (including polymerase chain reaction and mass spectrometry), and imaging modalities (including anterior segment optical coherence tomography and in vivo confocal microscopy). We also highlight the potential roles of emerging technologies such as next-generation sequencing, artificial intelligence-assisted platforms. and tele-medicine in shaping the future diagnostic landscape of IK.

Efficient nested-PCR-based method development for detection and genotype identification of Acanthamoeba from a small volume of aquatic environmental sample

Acanthamoeba spp. are opportunistic human pathogens that cause granulomatous amoebic encephalitis and keratitis, and their accurate detection and enumeration in environmental samples is a challenge. In addition, information regarding the genotyping of Acanthamoeba spp. using various PCR methods is equally critical. Therefore, considering the diverse niches of habitats, it is necessary to develop an even more efficient genotyping method for Acanthamoeba spp. detection. This study improved the sensitivity of detection to avoid underestimation of Acanthamoeba spp. occurrence in aquatic environmental samples, and to accurately define the pathogenic risk by developing an efficient PCR method. In this study, a new nested genotyping method was established and compared with various PCR-based methods using in silico, lab, and empirical tests. The in silico test showed that many PCR-based methods could not successfully align specific genotypes of Acanthamoeba, except for the newly designed nested PCR and real-time PCR method. Furthermore, 52 water samples from rivers, reservoirs, and a river basin in Taiwan were analysed by six different PCR methods and compared for genotyping and detection efficiency of Acanthamoeba. The newly developed nested-PCR-based method of genotyping was found to be significantly sensitive as it could effectively detect the occurrence of Acanthamoeba spp., which was underestimated by the JDP-PCR method. Additionally, the present results are consistent with previous studies indicating that the high prevalence of Acanthamoeba in the aquatic environment of Taiwan is attributed to the commonly found T4 genotype. Ultimately, we report the development of a small volume procedure, which is a combination of recent genotyping PCR and conventional real-time PCR for enumeration of aquatic Acanthamoeba and acquirement of biologically meaningful genotyping information. We anticipate that the newly developed detection method will contribute to the precise estimation, evaluation, and reduction of the contamination risk of pathogenic Acanthamoeba spp., which is regularly found in the water resources utilised for domestic purposes.

Parasitic keratitis - An under-reported entity

Parasitic keratitis (PK) is unique entity among parasitic infections where corneal involvement could result from direct inoculation of the parasite via exogenous environment or spread via endogenous neighboring organs or as a result of immune-mediated damage secondary to a systemic parasitic infection. Most cases of PK are caused by Acanthamoeba spp. and Microsporidia spp. though few other parasitic agents can also lead to corneal involvement. Mimicking as other infectious and non-infectious causes of keratitis, PK often escapes detection. This review summarizes the predominant causes of PK along with the epidemiological, clinical and microbiological details of each. Though several gaps exist in our understanding of the prevalence of PK, the one thing for sure is that PK is on the rise. With advanced diagnostic modalities and enough literature on optimal management of cases of PK, it is now imperative that a strong clinical suspicion of PK is kept when examining a case of corneal pathology and adequate investigations are ordered.

Development of Visually Improved Loop Mediated Isothermal Amplification for the Diagnosis of Plasmodium vivax Malaria in a Tertiary Hospital in Chandigarh, North India

More than 80% of the global burden of the Plasmodium vivax is contributed by mainly three countries (India, Indonesia, and Pakistan). Reports from last decades have highlighted the occurrence of severe P. vivax malaria which was earlier considered to be benign. The recent trends of increasing P. vivax-associated morbidity and mortality emphasizes the need for early and accurate diagnosis of P. vivax malaria for the timely management of patients. Microscopy is considered a gold standard but needs experienced laboratory technologists. Over the last few years, Polymerase chain reaction (PCR) is being used as a highly sensitive and specific test but it requires expensive equipment which limits its use in the field. Therefore, in the present study, utility of visually improved loop-mediated isothermal amplification (LAMP) for the detection of P. vivax was evaluated targeting 18SrRNA gene in 145 microscopically confirmed P. vivax and 20 P. vivax negative patients. Sensitivity and specificity of LAMP was assessed with respect to microscopy and multiplex nested PCR (nPCR). Results of the LAMP assay was also correlated with rapid diagnostic test, multiplex nPCR and real-time PCR results. Overall, sensitivity and specificity of P. vivax-specific LAMP compared with microscopy were found to be 100% and 85%, respectively. Furthermore, detection limit for LAMP was found to be 0.8 copies/μL and it was also able to detect three complicated cases of P. vivax which were missed by microscopy. This study showed a LAMP assay to be a rapid and very sensitive method for the early diagnosis of both complicated and uncomplicated P. vivax malaria.

Evaluation of hibergene loop-mediated isothermal amplification assay for detection of group B streptococcus in recto-vaginal swabs: a prospective diagnostic accuracy study

OBJECTIVES

To prospectively evaluate HiberGene's loop-mediated isothermal amplification (LAMP) assay for detection of group B streptococcus (GBS) in maternal recto-vaginal swabs and compare it with enrichment culture.

METHODS

Following ethical approval and informed written consent, two low vaginal and rectal swabs were obtained from 400 pregnant women. One swab was tested for GBS using the rapid LAMP assay (index test), the second swab was tested using enrichment culture (reference standard). Antimicrobial susceptibility testing was performed according to EUCAST guidelines.

RESULTS

There were 376 concordant results, 20 discordant and four invalid LAMP results. Among discordant results, six were LAMP negative/culture positive and 14 were LAMP positive/culture negative. The sensitivity was 92.2%, specificity 95.6%, positive predictive value 83.5% and negative predictive value 98.1%. The prevalence of GBS carriage was 19.25% (77/400). Forty-eight of 77 GBS-positive women were colonized vaginally (62.3%) and 70 were colonized rectally (90.9%). Erythromycin resistance was 22.4% (17/76) and clindamycin resistance was 17.1% (13/76).

CONCLUSIONS

The LAMP assay is a rapid and simple test with results available in approximately 1 h compared with 48 h for culture. The test has good sensitivity and specificity compared with enrichment culture. This test can be used for rapid antenatal GBS screening.

Non-contact lens related Acanthamoeba keratitis

The purpose of the study is to describe epidemiology, clinical features, diagnosis, and treatment of Acanthamoeba keratitis (AK) with special focus on the disease in nonusers of contact lenses (CLs). This study was a perspective based on authors' experience and review of published literature. AK accounts for 2% of microbiology-proven cases of keratitis. Trauma and exposure to contaminated water are the main predisposing factors for the disease. Association with CLs is seen only in small fraction of cases. Contrary to classical description experience in India suggests that out of proportion pain, ring infiltrate, and radial keratoneuritis are seen in less than a third of cases. Majority of cases present with diffuse infiltrate, mimicking herpes simplex or fungal keratitis. The diagnosis can be confirmed by microscopic examination of corneal scraping material and culture on nonnutrient agar with an overlay of Escherichia coli. Confocal microscopy can help diagnosis in patients with deep infiltrate; however, experience with technique and interpretation of images influences its true value. Primary treatment of the infection is biguanides with or without diamidines. Most patients respond to medical treatment. Corticosteroids play an important role in the management and can be used when indicated after due consideration to established protocols. Surgery is rarely needed in patients where definitive management is initiated within 3 weeks of onset of symptoms. Lamellar keratoplasty has been shown to have good outcome in cases needing surgery. Since the clinical features of AK in nonusers of CL are different, it will be important for ophthalmologists to be aware of the scenario wherein to suspect this infection. Medical treatment is successful if the disease is diagnosed early and management is initiated soon.