Evaluation of five automated and one manual method for Toxoplasma and human DNA extraction from artificially spiked amniotic fluid

OBJECTIVES

Molecular detection of Toxoplasma gondii plays a crucial role in the prenatal and neonatal diagnosis of congenital toxoplasmosis (CT). Sensitivity of this diagnosis is partly related to the efficiency of parasite DNA extraction and amplification. DNA extraction methods with automated platforms have been developed. Therefore, it is essential to evaluate them in combination with adequate PCR amplification assays.

METHODS

In this multisite study, we investigated the suitability of two recent automated procedures for the isolation of Toxoplasma DNA from amniotic fluid (AF) (Magtration system 12GC, PSS and Freedom EVO VacS, Tecan), compared with three other automated procedures (MagNAPure Compact, Roche, BioRobot EZ1, Qiagen and modified NucliSens easyMAG, bioMérieux) and with the manual DNA extraction QIAamp DNA Mini kit (Qiagen). Two Toxoplasma PCR assays targeting the '529-bp' repeat DNA element were used, based upon dual hybridization (FRET) or hydrolysis (TaqMan) probes. A total of 1296 PCRs were performed including 972 Toxoplasma PCRs.

RESULTS

We showed variable efficacy (4.2%-100% positive results) among the DNA extraction procedures in isolating up to five T. gondii cells/mL in AF samples. Moreover, for a given DNA extraction method, variable results were obtained among the two Toxoplasma PCR assays for detecting up to five T. gondii cells/mL: when using TaqMan PCR, all the automated systems yielded more than 60% positive results. Nevertheless, when testing the DNA extracts in triplicate, four out of six extraction methods allowed a satisfactory detection of low amounts of T. gondii DNA (≥33% of positive results) independently of the PCR assay used.

CONCLUSIONS

Despite the influence of the subsequent PCR method used, this study should help microbiologists in the choice of DNA extraction methods for the detection of T. gondii in amniotic fluid. The extraction method should be checked as adequate for the PCR assay used.

Pneumocystosis: a network survey in the Paris area 2003-2008

The aims of this network group were to collect epidemiological data of PcP cases in 14 hospitals in the Paris area and to determine the Di-Hydro Pteroate Synthase (DHPS) genotypes, genetic markers for possible sulfamide resistance. From January 1, 2003 to December 31, 2008, 993 (mean 166/year) PcP cases have been reported. Sixty-five percent of patients were HIV-positive. The median count of CD4 lymphocytes was 32/mm(3) (30 in HIV-positive patients, 152 in HIV-negative patients). In HIV-positive patients, PcP revealed the HIV infection in 39%. Among 304 PcP occurring in HIV known infected patients, no prophylaxis was prescribed for 64%; cotrimoxazole prophylaxis had been prescribed to 47 patients but only one of them had the right compliance. In HIV-negative patients (264), corticosteroids were prescribed in 59% and cytotoxic chemotherapies in 34%; 78% did not receive prophylaxis. One hundred sixty nine tumoral pathologies and 116 transplantations were notified. The mortality rate was 16% at day 14 (13% in HIV-positive patients, 26% in HIV-negative patients). Mutations in DHPS genes were detected in 18.5% of samples; 12.5% of patients were infected with several strains. The total annual number of cases has been stable for five years but the proportion of HIV-negative patients increased from 25% to 43%.

Factors of occurrence of ocular toxoplasmosis. A review

Acquired and congenital toxoplasmosis are frequently complicated by ocular toxoplasmosis. The diagnosis relies on clinical aspects, response to specific treatment and results of biological assays. The incidence and the prevalence of this complication are difficult to establish precisely and depend on the prevalence of the parasite infection in the general population, and are affected by factors such as type of exposure to the parasite, genetic backgrounds of the parasite and the host, and type of immune response elicited by the parasite.

[How can the cost of screening for toxoplasmosis during pregnancy be reduced?]

BACKGROUND

A program of systematic serology screening for toxoplasmosis during pregnancy has been running in France since 1978. The program involves monthly follow-ups for all non-immune pregnant women. Due to the steady decline in the seroprevalence of toxoplasmosis, the cost of the program is steadily increasing. Current screening is based on the detection of IgG and IgM isotypes. The aim of this work was to estimate the benefit of replacing combined dosage of two isotypes, by an alternative strategy that detects total anti-Toxoplasma immunoglobulins.

METHODS

The rate of decreasing seroprevalence and the increasing burden on serological examinations was measured in a study population of pregnant women who were checked for toxoplasmosis by the parasitology laboratory of the Cochin Hospital, Paris. The increase in screening costs was estimated for the all-pregnant women and the expected benefits stemming from simply measuring total anti-Toxoplasma immunoglobulins compared to the double IgG-IgM assay were estimated.

RESULTS

Between 1987 and 2008, the seroprevalence of toxoplasmosis measured at the Cochin hospital dropped from 70.8% to 48.6% with a 1.77% annual rate of decline. This downward trend is similar to that observed by the national perinatal surveys performed in 1995 and in 2003. As the number of non-immune women to follow-up each month is constantly increasing, the proportion of negative tests issued reached 87.6% in 2008. Extrapolating these results to the whole of France, we estimated that the number of required screening tests perform was increasing by 93,000 units per year with an additional associated cost of one million euros. Various alternative scenarios of antibody detection are proposed that could save between 40.2% and 48.4% of current screening costs.

CONCLUSION

Replacement of combined dosage of IgG and IgM isotypes by determination of just total Ig would significantly reduce costs of toxoplasmosis screening for pregnant women, without effecting either the general strategy, or proven efficiency of the national program.

Use of nuclear and mitochondrial DNA PCR and sequencing for molecular identification of Diphyllobothrium isolates potentially infective for humans

Tapeworms of the genus Diphyllobothrium (Cobold, 1858) are widely distributed all around the world and some of them are agents of human diphyllobothriasis. Approximately 50 species have been described within the Diphyllobothrium genus but only 13 are human pathogens. Species identification by using morphological criteria is very difficult. We determined the value of 18S ribosomal RNA gene, internal transcribed spacer (ITS) and cytochrome c oxidase subunit 1 gene (COI) sequences to differentiate between Diphyllobothrium isolates. Sequences from 18 isolates (larvae or adults) of D. latum, D. nihonkaiense, D. ditremum, D. dentriticum and D. stemmacephalum species were obtained. COI region sequences analysis was clearly more discriminative than those of the ITS1 and 18S rRNA and was a useful tool for identifying specimens.

Comparison of PCR, microscopic examination and culture for the early diagnosis and characterization of Acanthamoeba isolates from ocular infections

In the study presented here, PCR, microscopic examination and culture of corneal samples were compared as methods of confirming the clinical diagnosis of Acanthamoeba keratitis, a serious ocular infection that is difficult to diagnose and threatens eyesight. The three methods were applied to isolates obtained from 513 patients with clinical signs or risk factors suggesting Acanthamoeba infection. Acanthamoeba keratitis was diagnosed in 12 of these patients. Combined PCR assays were more sensitive (94%) than either microscopic examination (33%) or culture (7%). The Acanthamoeba isolates were characterized using DNA sequence analysis of the nuclear small-subunit rRNA gene, and T4 was the predominant genotype found.

Diagnostic par PCR des kératites à Acanthamoeba spp

AIM

Evaluation of a PCR assay as a diagnostic tool for detection of Acanthamoeba spp. in patients presenting infectious keratitis.

METHODS

Between August 2001 and November 2002, 342 clinical specimens consisting in corneal scrapings from 334 patients were tested for Acanthamoeba using direct microscopy, culture, and PCR. A fragment of Acanthamoeba 18S rRNA gene was amplified using a set of primers referred to as Nelson's primers.

RESULTS

A diagnosis of Acanthamoeba keratitis was considered for nine patients. Amoeba growth in culture was unfruitful for all of these cases. Eight patients had corneal scrapings that tested positive with PCR; in two cases direct microscopy observations confirmed PCR results. For one patient, a negative PCR result was obtained; however, a second corneal sample and cysts staining on May-Grünwald-Giemsa were positive. A false-positive PCR result was noted related to another amebic genus. A risk factor was found in all Acanthamoeba keratitis cases (contact lenses, trauma). Topical treatment was successful, and keratoplasty was necessary afterwards for optical rehabilitation in five patients.

CONCLUSION

This study suggests that PCR is a sensitive diagnostic tool, superior to conventional techniques for detecting Acanthamoeba in corneal lesions.

Polymicrobial candidaemia revealed by peripheral blood smear and chromogenic medium

Candida spp are the fourth most common group of nosocomial pathogens isolated from patients on medical, surgical, and intensive care wards. Polymicrobial candidaemia has rarely been described. The diagnosis of candidaemia from peripheral blood smears has not been widely reported. This report describes the case of a young woman suffering from Ewing's sarcoma who developed a syndrome of septic shock. Deep fungal infection was diagnosed from a systematic peripheral blood smear and yeasts were isolated within 24 hours. A subculture on CHROMagar Candida allowed the differentiation and presumptive identification of Candida tropicalis and Candida krusei. Species identification was confirmed by the ID 32C system. This report underlines the usefulness of peripheral blood smears in the diagnosis of fulminant deep fungal infections, and of a differential isolation medium in the rapid presumptive identification of clinically important yeast species from clinical samples. This medium is particularly useful for the detection of mixed fungal infections, allowing early and better adapted antifungal treatment.

Usefulness of immunoblotting and Goldmann-Witmer coefficient for biological diagnosis of toxoplasmic retinochoroiditis

Toxoplasmosis is a frequent cause of retinochoroiditis. Although the diagnosis relies mainly on ophthalmological examination, biological approaches are particularly useful in patients with atypical lesions. In a prospective study to determine the value of immunoblotting and immune load calculation in the diagnosis of active toxoplasmic retinochoroiditis, aqueous humor samples from 21 patients with retinochoroiditis and 5 control patients with cataracts were tested. Immune load was calculated on the basis of intraocular antibody production. The immune load ratio between aqueous humor and serum (Goldmann-Witmer coefficient) was significant (i.e. >2) in 9 of the 17 (53%) patients with retrospectively documented toxoplasmic retinochoroiditis. Immunoblotting suggested local antibody production in 10 of 17 (59%) patients. The combination of the two techniques gave a sensitivity of 71% (12/17). Both techniques were negative in the four patients in whom the final diagnosis of toxoplasmic retinochoroiditis was negative and in the five patients with cataracts. These results confirm the value of combining these two techniques. Moreover, immunoblotting has the advantages of being easy to perform and of requiring a very small sample.

Utilisation de 1' ivermectine en médecine tropicale

Ivermectin is a major breakthrough for the treatment of onchocerciasis, strongyloidosis, scabies and cutaneous larva migrans. Combined with albendazole, ivermectin is highly efficient for treating lymphatic filariasis and intestinal worms. Ivermectin shows very few side-effects but its use in children below 5 and during pregnancy is discussed. Ivermectin tolerance could be related to mdr1 gene expression. Additional studies are needed to assess its efficiency for pediculosis.

Mycetoma of the foot caused by Fusarium solani: identification of the etiologic agent by DNA sequencing

We report a case of Fusarium solani mycetoma of the foot that could not be diagnosed by culture, but was correctly identified after amplification and sequence analysis of fungal internal transcribed spacers 1 and 2 and 5.8S ribosomal DNA regions.

[Comparative evaluation of a latex agglutination test, two Elisa tests and a Western blot test for the serodiagnosis of human trichinellosis]

Serology is a helpful test for the diagnosis of human trichinellosis because clinical signs of this disease (fever and myalgias) are non specific. A lot of techniques have been studied but very few are commercialized and have been comparatively evaluated. We report here the performances of 4 commercially available kits: two Elisa tests, one western blot test & one latex agglutination test. The specificity and sensitivity of the different tests were assayed on 60 sera from patients with a proven trichinellosis and on 70 controls. The four tests had a 100% sensitivity. The specificity was of 98.6% for the western blot, of 93% for the latex agglutination test and of 87 & 77% for the two Elisa tests. Cross reactions are mainly observed in patients with other helminthic infections.

Contribution of serological tests and blood culture to the early diagnosis of systemic candidiasis

The isolation of Candida species from a single blood culture is considered sufficient evidence for the initiation of systemic antifungal therapy. However, blood cultures still lack sensitivity. Previous reports have suggested that the combined serological detection of mannanemia and anti-mannan antibodies may be useful for the diagnosis of systemic candidiasis caused by Candida albicans (specificity and sensitivity 93% and 80%, respectively). In this study, serological tests to detect Candida albicans mannan and Candida albicans antibodies (Platelia Candida Antigen and Antibody tests; Bio-Rad, France) were applied retrospectively to a series of patients with at least one Candida-positive blood culture and from whom at least one serum sample, taken before or on the day of blood culture, was available. Forty-five patients were selected, including 23 infected by Candida albicans, 4 by Candida glabrata, 9 by Candida tropicalis, 5 by Candida parapsilosis, and 4 by Candida krusei. Serological tests were positive in 73% of patients at least 2 days, and in some patients, up to 15 days before blood cultures became positive. These data suggest that serological surveillance of at-risk patients using the Platelia Candida tests could result in earlier initiation of antifungal therapy, especially when used in conjunction with blood cultures. In this way, more efficient management of nosocomial infections caused by Candida species can be achieved.