Single-step Polymerase Chain Reaction Research Articles

Novel molecular diagnostic technique for detecting the different species of Plasmodium

BackgroundSensitive diagnostic techniques are needed for timely detection of malaria parasite and disease control. Molecular diagnostic techniques involving Polymerase chain reaction (PCR) with 18 s rRNA as a known diagnostic target with an overall sensitivity of 10 parasites per microliter is used as a gold standard. Till date, no attempt has been undertaken to develop a technique for the identification of four Plasmodium species in a single step PCR combined with restriction digestion with enzymes. MethodPlasmodium species-specific polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assays have been developed, based on RFLP of amplified PCR product of mitochondrial gene as a target. This approach identifies Plasmodium species in two steps involving amplification of mitochondrial (Mt) gene by PCR followed by digestion with restriction enzymes. ResultA total of 36 clinical samples were subjected to PCR-RFLP for the diagnosis and detection of malaria parasites targeting mitochondrial gene (Mt). The findings of the method were compared with gold standard methods (Microscopy, RDTs and Nested PCR) and was able to detect mixed infection with a sensitivity of 100% and specificity of 93.8% with respect to nested PCR. The results obtained by PCR-RFLP were validated with Sanger sequencing (n = 32) and were found to be consistent with the method. ConclusionThis method identifies and distinguishes four species of human malaria parasite namely P. falciparum (Pf), P. vivax (Pv), P. malariae (Pm) and P. ovale (Po) in approximately 4 h. To overcome and address PCR difficulties, continuous efforts are needed for the development of newer diagnostic techniques.

A new method to quantify atmospheric Poaceae pollen DNA based on the trnT-F cpDNA region

Abstract Background Pollen, mold spores, bacteria and viruses are the main biological substances in the atmosphere causing allergic symptoms and disease. Distinguishing pollen and spores is quite time consuming and requires a trained expert. There is a different approach to identification of these substances such as microscopic analysis. However, DNA based identification of these is becoming popular recently. Objective We evaluated the correlation between the quantity of DNA, which was amplified using trnT-F cpDNA specific primers in samples obtained from a high volume air sampler (HVAS), and concentration of Poaceae pollen collected with a Burkard trap. Materials and methods Here, we present a method for identifying and quantifying airborne Poaceae pollen using a single step polymerase chain reaction (PCR) technique. Forty daily air samples were collected by HVAS. The method was optimised using two different methods (M1 and M2) and the trnT-F cpDNA region was amplified using a Poaceae specific primer pair. The correlation between the quantity of DNA and pollen concentration was tested using R statistical programming language. Results Although a significant correlation was obtained between the M1 and M2 methods (R2=0.655, p<0.01), the M2 method was more correlated with pollen concentration. The correlation between pollen and DNA content changed due to episodes that were observed during the pollen season. DNA concentrations from the PCR data were significantly correlated with pollen concentrations determined by light microscopy (R2=0.767, p<0.01) in episode II using the M2 method and during the entire season (R2=0.469, p<0.01) using M2. Conclusions The M2 method correctly identified Poaceae pollen in mixed air samples from Zonguldak Province. The non-coding trnT-F cpDNA region was used for the first time in aerobiological samples to identify Poaceae pollen. Use of this method that does not require DNA extraction may be a crucial step for real-time pollen monitoring devices to be developed in the future. The correlation strength between pollen and amplified DNA content could be improved using a sampler that has a lower absorption rate, and a more sensitive technique, such as qPCR.

Possible association between Helicobacter pylori infection and vocal fold leukoplakia.

Several studies have indicated the larynx as possible Helicobacter pylori (H. pylori) reservoirs. This study explored the association between H. pylori and vocal fold leukoplakia. The case-control study involved 51 patients with vocal fold leukoplakia and 35 control patients with vocal polyps. Helicobacter pylori was detected in tissues by the rapid urease test, nested polymerase chain reaction (PCR), and single-step PCR. The H. pylori-specific immunoglobulin antibodies were detected in plasma by enzyme-linked immunosorbent assay (ELISA). Helicobacter pylori-positive rate of vocal fold leukoplakia and vocal polyps was 23.5% versus 11.4% (P = .157), 37.2% versus 14.3% (P = .020), 27.5% versus 8.6% (P = .031), and 70.6% versus 68.6% (P = .841) detected by rapid urease test, nested PCR, single-step PCR, and ELISA, respectively. Regression analysis indicated that H. pylori infection (P = .044) was the independent risk factor for vocal fold leukoplakia. Helicobacter pylori infection exists in the larynx and may be associated with vocal fold leukoplakia.

Single-step blood direct PCR: A robust and rapid method to diagnose triplet repeat disorders

ObjectiveDNA extraction prior to polymerase chain reaction (PCR) amplification in genetic diagnoses of triplet repeat disorders (TRDs) is tedious and labour-intensive and has the limitations of sample contamination with foreign DNA, including that from preceding samples. Therefore, we aimed to develop a rapid, robust, and cost-effective method for expeditious genetic investigation of TRDs from whole blood as a DNA template. MethodsPeripheral blood samples were collected from 70 clinically suspected patients of progressive ataxia. The conventional method using genomic DNA and single-step Blood-Direct PCR (BD-PCR) method with just 2μl of whole blood sample were tested to amplify triplet repeat expansion in genes related to spinocerebellar ataxia (SCA) types 1, 2, 3, 12 and Friedreich's ataxia (FRDA). Post-PCR, the allele sizes were mapped and repeat numbers were calculated using GeneMapper and macros run in Microsoft Excel programmes. ResultsSuccessful amplification of target regions was achieved in all samples by both methods. The frequency of the normal and mutated allele was concordant between both methods, diagnosing 37% positive for a mutation in either of the candidate genes. The BD-PCR resulted in higher intensities of product peaks of normal and pathogenic alleles. ConclusionsThe nearly-accurate sizing of the normal and expanded allele was achieved in a shorter time (4–5h), without DNA extraction and any risk of cross contamination, which suggests the BD-PCR to be a reliable, inexpensive, and rapid method to confirm TRDs. This technique can be introduced in routine diagnostic procedures of other tandem repeat disorders.

Simplified Method of Detection of Dialister invisus and Olsenella uli in Oral Cavity Samples by Polymerase Chain Reaction

Aims and Objectives: The oral microbial flora is highly complex and diverse with obligate anaerobic bacteria as the predominant component. Most of these are not yet cultivated/difficult to cultivate due to technical limitations. In this study, we aim to detect two novel oral bacterial species Dialister invisus and Olsenella uli by simplified and economical procedure of polymerase chain reaction (PCR) and study their association with primary and persistent endodontic infections. Material and Methods: The study involved 60 patients that included 30 patients of primary endodontic infections and 30 with persistent endodontic infections. The sample collection from the root canal was performed by universally accepted protocol by using sterile paper points. The deoxyribonucleic acid (DNA) extraction was done, followed by PCR with species specific primers. We made several changes to the protocol mentioned by original authors. We adopted a one-step protocol for amplification of bacterial DNA, omitting the 16SrDNA amplification step with universal primers. Results: It was seen that 7 (23.3 %) samples in primary endodontic infection group and 24 (80 %) samples in persistent endodontic infection group were positive for D. invisus. On the other hand, 11 (36.6 %) patients of primary endodontic infection showed positivity for O. uli in comparison to 9 (30 %) of persistent endodontic infection. Conclusion: The results from the present study showed efficient amplification of both O. uli and D. invisus in a single-step PCR. Hence, we conclude that the modified protocol used here with taq polymerase enzyme offers a faster and cheaper alternative to nested PCR without compromising the quality of amplification process.

The presence of Helicobacter pylori in oral cavities of patients with leukoplakia and oral lichen planus.

ABSTRACTObjective Helicobacter pylori infection is one of the most common bacterial infections in men. This gastrointestinal pathogen is closely related to gastritis, peptic ulcers, and the increased risk of gastric cancer. Numerous studies have indicated oral cavities as possible Helicobacter pylori reservoirs. Helicobacter pylori has been detected both in supragingival and subgingival plaques, and also in saliva. In addition, the relationship between lesions of oral mucosa and the presence of H. pylori has been evaluated and described in some studies. The aim of this study was to assess the presence of Helicobacter pylori DNA in the oral cavity of patients with oral leukoplakia and oral lichen planus.Material and Methods The study included 54 patients with oral leukoplakia, 72 with oral lichen planus lesions, and 40 healthy controls. The presence of Helicobacter pylori in oral cavity samples was analyzed using a single-step Polymerase Chain Reaction (PCR) method. All patients underwent a periodontal examination and the following clinical parameters were collected: pocket depth, bleeding, and plaque indexes. The periodontal status was assessed using the Offenbacher classification.Results In most patients, pathological lesions were in typical sites on the buccal mucosa (leukoplakia in 88%, and oral lichen planus in 93% of patients). The DNA of the Helicobacter pylori was present in 20% of patients with leukoplakia and 23% of patients with lichen planus. We did not find the DNA of H. pylori in healthy controls. The periodontal status described by periodontal indices was worse in the investigated group than in the control group.Conclusion These findings suggest that the H. pylori presence in oral cavities may be related with leukoplakia and lichen planus oral lesions.

A Newly Developed Nested PCR Assay for the Detection of Helicobacter pylori in the Oral Cavity.

To develop a new nested polymerase chain reaction (PCR) assay for identifying Helicobacter pylori DNA from dental plaque. H. pylori is one of the most common chronic bacterial pathogens in humans. The accurate detection of this organism is essential for proper patient management and for the eradication of the bacteria following treatment. Forty-nine patients (24 males and 25 females; mean age: 51; range, 19 to 94 y) were investigated for the presence of H. pylori in dental plaque by single-step PCR and nested PCR and in the stomach by single-step PCR, nested PCR, and histologic examination. The newly developed nested PCR assay identified H. pylori DNA in gastric biopsies of 18 patients who were histologically classified as H. pylori-positive and 2 additional biopsies of patients who were H. pylori-negative by histologic examination (20/49; 40.8%). Dental plaque samples collected before and after endoscopy from the 49 patients revealed that single-step PCR did not detect H. pylori but nested PCR was able to detect H. pylori DNA in 40.8% (20/49) patients. Nested PCR gave a higher detection rate (40.8%, 20/49) than that of histology (36.7%, 18/49) and single-step PCR. When nested PCR results were compared with histology results there was no significant difference between the 2 methods. Our newly developed nested PCR assay is at least as sensitive as histology and may be useful for H. pylori detection in patients unfit for endoscopic examination.

Comparative evaluation of the GP5 +/6 +, MY09/11 and PGMY09/11 primer sets for HPV detection by PCR in oral squamous cell carcinomas

The aim of this study was to evaluate the use of GP5+/6+, MY09/11 and PGMY09/11 primer sets for the detection of human papillomavirus (HPV) DNA by single step polymerase chain reaction (PCR) and nested PCR in formalin-fixed and paraffin-embedded (FFPE) tissues from oral squamous cell carcinomas (OSCCs). DNA extracted from FFPE tissues were tested for amplification of the human beta globin gene with PCO3/4 primers. Positive samples for this gene were tested for HPV DNA using single step PCR with GP5+/6+, MY09/11 and PGMY09/11 primer sets. All negative samples at single step PCR with MY09/11 and PGMY09/11 were subjected to a further PCR with GP5+/6+ primers using the non-amplified product in the previously reactions (nested PCR) as samples. Among 26 samples, 23 were positive for the human beta globin gene and were considered viable for HPV DNA detection by PCR. Single step PCR with GP5+/6+ and MY09/11 primers and MY/GP+ nested PCR did not amplify HPV DNA in any samples. PGMY09/11 primers detected HPV DNA in 13.0% of OSCC cases and this rate was raise to 17.4% with the use of PGMY/GP+ nested PCR. According to our results the PGMY/GP+ nested PCR is the most appropriate primer set for the detection of HPV DNA using FFPE samples from OSCC.

Authentication of goat (Capra hircus) meat using PCR amplification of mitochondrial cytochrome b gene

A highly specific single step polymerase chain reaction (PCR) is described for the detection of goat (Capra hircus) meat. A PCR assay was successfully optimized for amplification of 617-bp DNA fragment extracted from goat meat using designed species-specific primer pairs based on mitochondrial cytochrome b gene. The optimized PCR assay was subsequently validated for its specificity with DNA extracted from cattle, buffalo, sheep, goat and pig. PCR amplification of target DNA with goat-specific primers was repeated 10 times, with consistent results observed. The specificity of goat-specific PCR provides a valuable tool for identification of goat meat and to avoid its fraudulent substitution and adulteration.

Diagnosis and treatment of Clostridium difficile in adults: a systematic review.

Since 2000, the incidence and severity of Clostridium difficile infection (CDI) have increased. To review current evidence regarding best practices for the diagnosis and treatment of CDI in adults (age ≥ 18 years). Ovid MEDLINE and Cochrane databases were searched using keywords relevant to the diagnosis and treatment of CDI in adults. Articles published between January 1978 and October 31, 2014, were selected for inclusion based on targeted keyword searches, manual review of bibliographies, and whether the article was a guideline, systematic review, or meta-analysis published within the past 10 years. Of 4682 articles initially identified, 196 were selected for full review. Of these, the most pertinent 116 articles were included. Clinical trials, large observational studies, and more recently published articles were prioritized in the selection process. Laboratory testing cannot distinguish between asymptomatic colonization and symptomatic infection with C difficile. Diagnostic approaches are complex due to the availability of multiple testing strategies. Multistep algorithms using polymerase chain reaction (PCR) for the toxin gene(s) or single-step PCR on liquid stool samples have the best test performance characteristics (for multistep: sensitivity was 0.68-1.00 and specificity was 0.92-1.00; and for single step: sensitivity was 0.86-0.92 and specificity was 0.94-0.97). Vancomycin and metronidazole are first-line therapies for most patients, although treatment failures have been associated with metronidazole in severe or complicated cases of CDI. Recent data demonstrate clinical success rates of 66.3% for metronidazole vs 78.5% for vancomycin for severe CDI. Newer therapies show promising results, including fidaxomicin (similar clinical cure rates to vancomycin, with lower recurrence rates for fidaxomicin, 15.4% vs vancomycin, 25.3%; P = .005) and fecal microbiota transplantation (response rates of 83%-94% for recurrent CDI). Diagnostic testing for CDI should be performed only in symptomatic patients. Treatment strategies should be based on disease severity, history of prior CDI, and the individual patient's risk of recurrence. Vancomycin is the treatment of choice for severe or complicated CDI, with or without adjunctive therapies. Metronidazole is appropriate for mild disease. Fidaxomicin is a therapeutic option for patients with recurrent CDI or a high risk of recurrence. Fecal microbiota transplantation is associated with symptom resolution of recurrent CDI but its role in primary and severe CDI is not established.

Molecular diagnosis of eosinophilic meningitis due to Angiostrongylus cantonensis (Nematoda: Metastrongyloidea) by polymerase chain reaction-DNA sequencing of cerebrospinal fluids of patients

Cerebrospinal fluid (CSF) samples from clinically diagnosed patients with detectable Angiostrongylus canto-nensis-specific antibodies (n = 10), patients with clinically suspected cases that tested negative for A. cantonensis-an-tibodies (n = 5) and patients with cerebral gnathostomiasis (n = 2) and neurocysticercosis (n = 2) were examined by a single-step polymerase chain reaction (PCR) method using the AC primers for the 66-kDa native protein gene. The PCR method detected A. cantonensis DNA in CSF samples from four of 10 serologically confirmed angiostrongyliasis cases. The PCR results were negative for the remaining CSF samples. The nucleotide sequences of three positive CSF-PCR samples shared 98.8-99.2% similarity with the reference sequence of A. cantonensis. These results indicate the potential application of this PCR assay with clinical CSF samples for additional support in the confirmation of eosinophilic meningitis due to A. cantonensis.

A single-step polymerase chain reaction for simultaneous detection and differentiation of nontypeable and serotypeable Haemophilus influenzae, Moraxella catarrhalis and Streptococcus pneumoniae

ObjectiveThe critically high prevalence of bacterial otitis media worldwide has prompted a proper disease management. While vaccine development for otitis media is promising, the reliable and effective methods for diagnosis of such etiologic agents are of importance. MethodsWe developed a multiplex polymerase chain reaction assay for simultaneous detection and differentiation of nontypeable and serotypeable Haemophilus influenzae, Moraxella catarrhalis and Streptococcus pneumoniae. Five primer pairs targeting genes fumarate reductase (H. influenzae), outer membrane protein B (M. catarrhalis), major autolysin (S. pneumoniae), capsulation-associated BexA protein (all encapsulated H. influenzae) and 16S rRNA were incorporated in this single-step PCR. Validation of the multiplex PCR was also performed on clinical isolates. ResultsThe developed multiplex PCR was highly specific, enabling the detection of the target pathogens in a specific manner, either individually or as a mixture of all target organisms. The assay was also found to be sensitive with the lowest detection limit of 1ng of bacterial DNA. When applied to clinical isolates from diverse specimen sources, the multiplex PCR developed in this study correctly identified each microorganism individually or in a combination of two or more target organisms. All results matched with conventional culture identification. In addition, the ability of such assay to differentiate H. influenzae encapsulation from the study clinical isolates was 100%. ConclusionOur multiplex PCR provides a rapid and accurate diagnostic tool for detection of the 4 target organisms. Such assay would serve as a useful tool for clinicians and epidemiologists in their efforts to the proper treatment and disease management caused by these organisms.

English

  A highly specific single step polymerase chain reaction (PCR) is described for the detection of pig (Sus domesticus) meat. A PCR assay was successfully optimized for amplification of 629 and 322-bp DNA fragment extracted from pig meat using designed species-specific primer pairs based on mitochondrial D-loop and 12Sribosomal ribonucleic acid (rRNA) gene, respectively. The optimized PCR assay was subsequently validated for its specificity with deoxyribonucleic acid (DNA) extracted from cattle, buffalo, sheep, goat and pig. PCR amplification of target DNA with pig-specific primers was repeated 15 times, with consistent results observed. The specificity of pig-specific PCR provides a valuable tool for identification of pig meat and to avoid its fraudulent substitution and adulteration.   Key words: Pig meat, adulteration, polymerase chain reaction (PCR), mitochondrialD-Loop, 12S ribosomal ribonucleic acid (rRNA) gene

English

  Brucellosis is an important disease affecting mainly sheep and goats. Diagnosis based on isolation of Brucella organisms from the suspected animals is the golden standard but has a limited sensitivity, expensive and unpractical to apply on a large scale in control campaigns. Accordingly, the indirect diagnosis of disease based on serological tests is the method of choice in the eradication programs. In this study, a single step polymerase chain reaction (PCR) was used to diagnose brucellosis using sheep whole blood and compared its sensitivity and specificity against some of the most commonly used serological techniques and modified ones. Three hundred apparently healthy ewes were randomly chosen from different governorates of Egypt. Sera were tested against Rose Bengal test (RBT), Serum Agglutination test (SAT), ELISA using both the whole Brucellaantigen (W-ELISA) and the periplasmic protein antigen (P-ELISA). Results showed that 39% of the blood samples were positive to the PCR test, Meanwhile 29.3, 27.0, 28.7 and 28.3% were positive to the previous serological tests respectively. We recommend the use of this blood PCR assay for accurate diagnosis of ovine brucellosis especially in the early stage of infection, which is difficult to achieve by the applied serological tests.   Key words: Ovine brucellosis, Blood PCR, RBT, SAT, ELISA.

Effect of processing treatments on the white spot syndrome virus DNA in farmed shrimps (Penaeus monodon)

To investigate the effect of processing treatments on the destruction of white spot syndrome virus (WSSV) DNA in WSSV-infected farmed shrimps (Penaeus monodon). The presence of WSSV was tested by single step and nested polymerase chain reaction (PCR). The primers 1s5 & 1a16 and IK1 & IK2 were used for the single step PCR and primers IK1 & IK2-IK3 & IK4 were used for the nested PCR. Various processing treatments such as icing, freezing, cooking, cooking followed by slow freezing, cooking followed by quick freezing, canning, and cold storage were employed to destroy the WSSV DNA. Of the processing treatments given, cooking followed by quick freezing was efficient in destroying WSSV DNA in WSSV-infected shrimp products. Canning, and cooking followed by slow freezing process had some destructive effect on the WSSV DNA, as WSSV DNA in such processed shrimp products was detected only by nested PCR. Icing, slow freezing, quick freezing, and cooking processes had no effect on the destruction of WSSV DNA. A gradual increase in the destruction of WSSV DNA was observed as the cold storage period increased. The results indicated that cooking followed by quick freezing process destroy the WSSV DNA. WSSV can be destroyed by cooking followed by quick freezing and this combined process can reduce the disease transmission risks from commodity shrimps to native shrimps.

A highly specific PCR assay for identification of goat (Capra hircus) meat

A highly specific single step polymerase chain reaction (PCR) is described for the detection of goat ( Capra hircus) meat. Goat-specific primers (DAF-01 and DGR-04) were designed against a conserved region of mitochondrial d-loop gene that yielded a 294 bp PCR product. Specificity of the primers was confirmed by testing them with DNA from other commonly used meat animal species, i.e., cattle, buffalo, sheep, swine and poultry. PCR amplification of target DNA with goat-specific primers was repeated 15 times, with consistent results observed. The specificity of goat-specific PCR provides a valuable tool for identification of goat meat and to avoid its fraudulent substitution and adulteration.

High occurrence of cyclosporiasis in Istanbul, Turkey, during a dry and warm summer

We evaluated the incidence of Cyclospora cayetanensis in immunocompetent, diarrheic patients during the summers of 2006-2009 in Istanbul. Stools from 1876 patients were examined using microscopic techniques. Cyclospora oocysts were observed in wet preparations by light and epifluorescence microscopy and in fecal smears that were stained by Kinyoun's modified acid-fast stain. Characteristic Cyclospora oocysts were observed in 2 patients in 2006, 17 in 2007, and one in 2009. Samples positive for Cyclospora were further analyzed by a single step polymerase chain reaction (PCR) with Cyclospora-specific primers from the ITS-1 region of the genome.The majority of the Cyclospora positive cases (15) were clustered during about 15 days in June 2007, indicating an unusual incidence of cyclosporiasis in this time period. The climatic characteristics of 2007 could have played a role in this high occurrence rate.

Infectious Salmon Anaemia Virus (ISAV) Ringtest: Validation of the ISAV Diagnositic Process using Virus-spiked Fish Tissues and ISAV TaqMan® Real-time RT-PCR

The incidence of white spot syndrome virus (WSSV) in the Indian farmed frozen shrimp products viz., whole, headless (HL) and peeled and undeveined (PUD) by polymerase chain reaction (PCR) was studied. The viability of WSSV in farmed frozen shrimps was investigated by conducting bio-inoculation studies. The products were screened for WSSV by both the single step (for the primer sets 1s5 & 1a16 and IK1 & IK2) and nested PCR (for the primers IK1 & IK2 - IK3 & IK4). Single step PCR detected WSSV in 18% of samples, while the nested PCR detected WSSV in 73% of samples. The frozen material, which gave positive results for WSSV by PCR, was further confirmed for the viability of WSSV by the bio-inoculation studies. Mortality (100%) was observed within the 45 h of intra-muscular post injection (P.I) into the healthy wild live WSSV-free shrimps (Penaeus monodon). These results show that the WSSV survived the freezing process and the cold storage and could cause infection in native shrimp farms if such products are reprocessed in the importing countries.

Rapid Detection of Fungal Keratitis with DNA-Stabilizing FTA Filter Paper

Purpose. Polymerase chain reaction (PCR) is increasingly important for the rapid detection of fungal keratitis. However, techniques of specimen collection and DNA extraction before PCR may interfere with test sensitivity. The purpose of this study was to investigate the use of DNA-stabilizing FTA filter paper (Indicating FTA filter paper; Whatman International, Ltd., Maidstone, UK) for specimen collection without DNA extraction in a single-step, nonnested PCR for fungal keratitis. Methods. Specimens were collected from ocular surfaces with FTA filter discs, which automatically lyse collected cells and stabilize nucleic acids. Filter discs were directly used in single-step PCR reactions to detect fungal DNA. Test sensitivity was evaluated with serial dilutions of Candida albicans, Fusarium oxysporum, and Aspergillus fumigatus cultures. Test specificity was analyzed by comparing 196 and 155 healthy individuals from Switzerland and Egypt, respectively, with 15 patients with a diagnosis of microbial keratitis. Results. PCR with filter discs detected 3 C. albicans, 25 F. oxysporum, and 125 A. fumigatus organisms. In healthy volunteers, fungal PCR was positive in 1.0% and 8.4% of eyes from Switzerland and Egypt, respectively. Fungal PCR remained negative in 10 cases of culture-proven bacterial keratitis, became positive in 4 cases of fungal keratitis, but missed 1 case of culture-proven A. fumigatus keratitis. Conclusions. FTA filter paper for specimen collection together with direct PCR is a promising method of detecting fungal keratitis. The analytical sensitivity is high without the need for a semi-nested or nested second PCR, the clinical specificity is 91.7% to 99.0%, and the method is rapid and inexpensive.

Diagnostic significance of nested polymerase chain reaction for sensitive detection of Pneumocystis jirovecii in respiratory clinical specimens

A total of 327 clinical specimens, including both invasive and noninvasive samples, obtained from 275 patients with various types of underlying immunocompromised conditions and a clinical suspicion of Pneumocystis pneumonia (PCP) were subjected to 2 different nested polymerase chain reaction (PCR) assays. The target genes used for nested PCR were mitochondrial large subunit ribosomal RNA (mtLSU rRNA) and internal transcribed spacer (ITS) region. The results were compared with a single-round PCR targeting major surface glycoprotein (MSG) gene. Amplification was successful in 16% of cases by mtLSU rRNA nested PCR, in 14.5% by ITS nested PCR, and in 10.9% by MSG PCR. The nested mtLSU rRNA PCR was found to be more sensitive (100% sensitive and 98.7% specific) and useful in detecting PCP for its use in routine diagnosis in our settings. Thus, this assay may be quite useful in the identification of patients who are in the early stage of Pneumocystis jirovecii infection with an organism load that could not be easily detected by the single-step PCR.