Diagnostic biologique des candidoses systémiques : difficultés et perspectives

A Real Time PCR strategy for the detection and quantification of Candida albicans in human blood

Candidemia is a significant cause of bloodstream infections (BSI) in nosocomial settings. The identification of species can potentially improve the quality of care and decrease human mortality. Quantitative PCR (qPCR) was evaluated for Candida albicans detection using culture suspensions containing C. albicans , spiked human blood, the cloned qPCR target fragment (ITS2 region) and the results of these assays were compared. The assays showed a good detection limit: C. albicans DNA extracted from yeast (sensitivity 0.2 CFU/µL), spiked human blood (sensitivity 10 CFU/mL), and cloned fragment of ITS2 region (sensitivity 20 target copies/μL). The efficiency of ITS2 fragment-qPCR ranged from 89.67 to 97.07, and the linearity (R²) of the standard curve ranged from 0.992 to 0.999. The results showed that this ITS2-qPCR has a great potential as a molecular prototype model for the development of a test to be applied in clinical practice, greatly reducing the time of candidemia diagnosis, which is extremely important in this clinical setting.

Mouse model of invasive fungal infection

The mouse intravenous (IV) challenge model of Candida albicans invasive fungal infection has been widely used to study the importance of the innate immune system in these infections. This chapter describes this well-characterized model, where fungal cells are administered directly into the mouse bloodstream to initiate a systemic infection. The preparation of tissue samples from infected mice to allow evaluation of disease progression and host responses is also described.

[Systemic candidiasis in medical intensive care unit: analysis of risk factors and the contribution of colonization index]

OBJECTIVES

Description of the epidemiological and clinical characteristics of the patients introducing risk factors of invasive candidiasis. Analysis of risk factors for candidiasis invasive and evaluation of the contribution of colonization index (CI) in the diagnosis of the systematic candidiasis in medical intensive care.

PATIENTS AND METHODS

Prospective observational study (October 2007 to October 2009). The selected patients present risk factors of system IC candidiasis with an infectious syndrome or clinical signs suggestive of Candida infection and hospitalized more than 48 hours in medical intensive care unit. Pittet's colonization index was calculated at admission and then once a week added to a blood culture. Patients were classified according to level of evidence of Candida infection and the degree of colonization (CI<0.5, CI ≥ 0.5).

RESULTS

The study included 100 patients. Mean age of our patients was 55.8 ± 18.2 years with male prevalence. Neurological disease was the most frequent pathology in admission (48%). The most common risk factors were broad-spectrum antibiotics and foreign material. In the various mycology IC specimens, Candida albicans was the most frequent, followed by C. tropicalis, then C. glabrata. The CI was greater than or equal to 0.5 at 53% of the patients, and less than 0.5 in 47% of the cases. Among the patients, 15% developed an invasive candidiasis. In multivariate analysis, the corticosteroid therapy was associated with a high colonisation (IC ≥ 0.5) and neutropenia with a high risk of systemic candidiasis. The positive predictive value of CI was 26%. The negative predictive value was 98%, the sensitivity and specificity was 93% and 48% respectively.

CONCLUSION

CI has the advantage to provide a quantified data of the patient's situation in relation to the colonization. But, it isn't helpful with patients having an invasive candidiasis in medical intensive care unit.

High-throughput identification and quantification of Candida species using high resolution derivative melt analysis of panfungal amplicons

Fungal infections pose unique challenges to molecular diagnostics; fungal molecular diagnostics consequently lags behind bacterial and viral counterparts. Nevertheless, fungal infections are often life-threatening, and early detection and identification of species is crucial to successful intervention. A high throughput PCR-based method is needed that is independent of culture, is sensitive to the level of one fungal cell per milliliter of blood or other tissue types, and is capable of detecting species and resistance mutations. We introduce the use of high resolution melt analysis, in combination with more sensitive, inclusive, and appropriately positioned panfungal primers, to address these needs. PCR-based amplification of the variable internal transcribed regions of the rDNA genes generates an amplicon whose sequence melts with a shape that is characteristic and therefore diagnostic of the species. Simple analysis of the differences between test and reference melt curves generates a single number that calls the species. Early indications suggest that high resolution melt analysis can distinguish all eight major species of Candida of clinical significance without interference from excess human DNA. Candida species, including mixed and novel species, can be identified directly in vaginal samples. This tool can potentially detect, count, and identify fungi in hundreds of samples per day without further manipulation, costs, or delays, offering a major step forward in fungal molecular diagnostics.

Use of recombinant antigens for the diagnosis of invasive candidiasis

Invasive candidiasis is a frequent and often fatal complication in immunocompromised and critically ill patients. Unfortunately, the diagnosis of invasive candidiasis remains difficult due to the lack of specific clinical symptoms and a definitive diagnostic method. The detection of antibodies against different Candida antigens may help in the diagnosis. However, the methods traditionally used for the detection of antibodies have been based on crude antigenic fungal extracts, which usually show low-reproducibility and cross-reactivity problems. The development of molecular biology techniques has allowed the production of recombinant antigens which may help to solve these problems. In this review we will discuss the usefulness of recombinant antigens in the diagnosis of invasive candidiasis.