Leticia Bernal-Martinez

Value of serial quantification of fungal DNA by a real-time PCR-based technique for early diagnosis of invasive aspergillosis in patients with febrile neutropenia.

ABSTRACT A study was designed to assess the reliability of the serial detection of Aspergillus sp. DNA to diagnose invasive aspergillosis (IA) in patients with febrile neutropenia. Two blood and two serum samples were taken weekly from 83 patients. A total of 2,244 samples were analyzed by real-time quantitative PCR. Twelve (14.4%) patients were diagnosed with IA. Taking two consecutive positive results as the diagnostic criterion, PCR detected 11 cases, with 4 false positives, giving sensitivity, specificity, positive, and negative predictive values of 91.6%, 94.4%, 73.3%, and 98.5%, respectively. On analyzing in conjunction with high-resolution chest tomography (HRCT) and galactomannan (GM) testing, the combination of serial PCR and GM detected 100% of aspergillosis cases, with a positive predictive value of 75.1%. This diagnostic strategy presented, according to CART analysis, a receiver-operator curve with an area under the curve of 0.97 (95% confidence interval, 0.895 to 1.032; P < 0.01), with a relative risk of IA 6.92 times higher than the control population and with predictive success of 95.2%. As regards early diagnosis, the serial detection of Aspergillus DNA took on average 21 days less than HRCT and 68 days less than GM. The serial detection of Aspergillus DNA using real-time quantitative PCR has great diagnostic applicability, which increases when combined with GM quantification.

The non-mammalian host Galleria mellonella can be used to study the virulence of the fungal pathogen Candida tropicalis and the efficacy of antifungal drugs during infection by this pathogenic yeast

Although Candida tropicalis is a frequent cause of invasive fungal diseases, its interaction with the host remains poorly studied. Galleria mellonella is a Lepidoptera model which offers a useful tool to study virulence of different microorganisms and drug efficacy. In this work we investigated the virulence of C. tropicalis in G. mellonella at different temperatures and the efficacy of antifungal drugs in this infection model. When larvae were infected with yeast inocula suspensions of different concentrations (4 × 10(6), 2 × 10(6), 10(6) and 5 × 10(5) cells/larva), we observed a dose-dependent effect on the killing of the insect (50% survival ranging from 1.4 ± 0.8 to 8.8 ± 1.2 days with the higher and lower inocula, respectively). Candida tropicalis killed G. mellonella larvae at both 30°C and 37°C, although at 37°C the virulence was more evident. Haemocytes phagocytosed C. tropicalis cells after 2 hours of infection, although the phagocytosis rate was lower when compared with other fungal pathogens, such as Cryptococcus neoformans. Moreover, the haemocyte density in the haemolymph decreased during infection and the yeast formed pseudohyphae in G. mellonella. The efficacy of amphotericin B, caspofungin, fluconazole and voriconazole was tested at different concentrations, and a protective effect was observed with all the drugs at concentrations equivalent to therapeutic dose. Fungal burden increased in infected larvae during time of infection and amphotericin B and fluconazole reduced the number of colony-forming units in the worms. Moreover, antifungal treatment was associated with the presence of cell aggregates around infected areas. We conclude that G. mellonella offers a simple and feasible model to study C. tropicalis virulence and drug efficacy.

In Vitro Activities of 35 Double Combinations of Antifungal Agents against Scedosporium apiospermum and Scedosporium prolificans

ABSTRACT Activities of 35 combinations of antifungal agents against Scedosporium spp. were analyzed by a checkerboard microdilution design and the summation of fractional concentration index. An average indifferent effect was detected apart from combinations of azole agents and echinocandins against Scedosporium apiospermum. Antagonism was absent for all antifungal combinations against both species.

Histoplasmosis and Paracoccidioidomycosis in a Non-Endemic Area: A Review of Cases and Diagnosis

BACKGROUND Histoplasmosis and paracoccidioidomycosis (PCM) have increased in Spain in recent years, due firstly to the migration from endemic regions and secondly to travelers returning from these regions. In non-endemic areas, diagnosis of both diseases is hampered by the lack of experience, long silent periods, and the resemblance to other diseases such as tuberculosis and sarcoidosis. METHODS A total of 39 cases of imported histoplasmosis and 6 cases of PCM diagnosed in the Spanish Mycology Reference Laboratory since 2006 were analyzed. Microbiological diagnosis was performed using classical methods and also a specific real-time polymerase chain reaction (RT-PCR) assay for each microorganism. RESULTS We had 9 cases of probable histoplasmosis in travelers and 30 cases in immigrants, 29 of whom were defined as proven. Paracoccidioidomycosis (PCM) cases were either immigrants or people who had lived for a long period of time in endemic regions, all of whom were classified as proven cases. Cultures showed a good sensitivity in detecting Histoplasma capsulatum in immigrants with proven histoplasmosis (73%); however, growth was very slow. The fungus was never recovered in traveler patients. Paracoccidioides brasiliensis was isolated in a culture only in one case of the proven PCM. Serological methods were not very reliable in immunocompromised patients with histoplasmosis (40%). A PCR-based technique for histoplasmosis detected 55.5% of the cases in travelers (probable cases) and 89% of the cases in immigrants (proven). The PCR method for PCM detected 100% of the cases. CONCLUSIONS These kinds of mycoses are increasingly frequent in non-endemic areas, and newer and faster techniques should be used to reach an early diagnosis. The RT-PCR techniques developed appear to be sensitive, specific, and fast and could be helpful to detect those mycoses. However, it is also essential that physicians perform differential diagnosis in individuals coming from endemic areas.

Update on the epidemiology and diagnosis of invasive fungal infection

In recent years, the most important advances in the treatment of transplant recipients, patients with haematological neoplasm and critically ill patients have been accompanied by an increase in the incidence of common fungal diseases and the emergence of some less common ones. Although new techniques (e.g. galactomannan detection) and new antifungals have appeared, these opportunistic infections remain difficult to diagnose and have a high mortality. New diagnostic techniques could improve this outlook, although they are far from becoming available in daily practice.

Development and Validation of a Quantitative PCR Assay for Diagnosis of Scedosporiosis

ABSTRACT Scedosporium apiospermum and Scedosporium prolificans are fungal pathogens that can cause severe human infections, including disseminated mycosis in immunocompromised patients. Two real-time PCR (RT-PCR) assays for the diagnosis of these species were developed and validated for the classification of clinical strains and for the detection of DNA in clinical samples by use of a murine model of invasive infection. A total of 14 clinical strains and 141 samples, including blood, serum, and lung samples from infected CD1 mice, were analyzed. Each RT-PCR methodology used a species-specific molecular beacon probe targeting a highly conserved region of the fungal ribosomal DNA gene. Results showed 100% specificity and a detection limit of 10 fg of DNA for both assays. The sensitivities for the S. prolificans-specific PCR assay were 100% for cultured clinical strains, 95.5% for lung tissues, 85% for serum, and 83.3% for blood. For S. apiospermum, the sensitivities were 100% for clinical strains and 97.2%, 81.8%, and 54.5% for lung tissues, serum, and blood, respectively. Both techniques can be useful for clinical diagnosis, and further studies are warranted.

Efficacy of DNA amplification in tissue biopsy samples to improve the detection of invasive fungal disease

The performance of a pan-fungal PCR-based technique was evaluated to assess the aetiology of invasive fungal diseases (IFDs). A total of 89 formalin-fixed paraffin-embedded biopsy samples from 84 patients with proven IFD were studied. Culture of tissue was performed in 68 (81%) patients. The sensitivities of the PCR-based technique and microbiological culture of tissues were 89% and 56%, respectively (p <0.01). According to PCR results, Aspergillus species accounted for 67%, Candida species for 13%, zygomycetes for 11%, and rare and emerging fungi for 9%. Aspergillus species were significantly associated with lung samples (79.6%, p <0.01), Mucorales were associated with skin/subcutaneous samples, and Candida species were associated with gastrointestinal samples. Regarding biopsy samples with Aspergillus species, Aspergillus fumigatus DNA was detected in 43 of 50 (86%), and Aspergillus flavus in six of 50 (12%). PCR was positive in 24 of 30 (80%) cases with negative culture. In nine of the 84 patients, the PCR technique failed to amplify the DNA. Six also had negative cultures, and in the remaining three cases culture was positive (Rhizopus microsporus, Rhizopus arrhizus, and Sakseneae vasiformis), suggesting that the PCR technique was not as effective in amplifying the DNA of some species of Zygomycetes. In five cases, there was no correlation between culture results and those obtained with DNA amplification, indicating the possibility of a mixed infection or the presence of colonizer/contaminant microorganisms. In summary, PCR-based techniques for DNA amplification should be implemented in histopathology and microbiology departments, as they appear to be complementary to conventional methods for IFD detection.

Candida tropicalis Antifungal Cross-Resistance Is Related to Different Azole Target (Erg11p) Modifications

ABSTRACT Candida tropicalis ranks between third and fourth among Candida species most commonly isolated from clinical specimens. Invasive candidiasis and candidemia are treated with amphotericin B or echinocandins as first-line therapy, with extended-spectrum triazoles as acceptable alternatives. Candida tropicalis is usually susceptible to all antifungal agents, although several azole drug-resistant clinical isolates are being reported. However, C. tropicalis resistant to amphotericin B is uncommon, and only a few strains have reliably demonstrated a high level of resistance to this agent. The resistance mechanisms operating in C. tropicalis strains isolated from clinical samples showing resistance to azole drugs alone or with amphotericin B cross-resistance were elucidated. Antifungal drug resistance was related to mutations of the azole target (Erg11p) with or without alterations of the ergosterol biosynthesis pathway. The antifungal drug resistance shown in vitro correlated very well with the results obtained in vivo using the model host Galleria mellonella. Using this panel of strains, the G. mellonella model system was validated as a simple, nonmammalian minihost model that can be used to study in vitro-in vivo correlation of antifungals in C. tropicalis. The development in C. tropicalis of antifungal drug resistance with different mechanisms during antifungal treatment has potential clinical impact and deserves specific prospective studies.

Susceptibility profile of clinical isolates of non-Cryptococcus neoformans/non-Cryptococcus gattii Cryptococcus species and literature review.

The in vitro susceptibility profile of 24 clinical isolates of non-Cryptococcus neoformans/non-Cryptococcus gattii Cryptococcus species was analysed. In addition, the susceptibility results of 98 other strains from seven different reports were reviewed. The latter included studies which used antifungal susceptibility testing reference procedures or commercial methods which exhibited high correlation rates with the reference procedures. A total of 122 isolates were analysed (57 Cryptococcus albidus, 39 Cryptococcus laurentii, ten Cryptococcus uniguttulatus, ten Cryptococcus humicola, four Cryptococcus curvatus, and two Cryptococcus luteolus). Amphotericin B was in vitro the most active compound against all species, while flucytosine and candins were inactive. Fluconazole exhibited a limited in vitro activity, particularly against C. albidus, C. uniguttulatus and C. laurentii. Voriconazole, itraconazole and posaconazole were active against most of isolates, but we found significant rates of decreased susceptibility. Identification and susceptibility testing of Cryptococcus spp. should be performed on a routine basis in view of their unpredictable susceptibility profiles.

Development of a single tube multiplex real-time PCR to detect the most clinically relevant Mucormycetes species

Mucormycetes infections are very difficult to treat and a delay in diagnosis could be fatal for the outcome of the patient. A molecular diagnostic technique based on Real Time PCR was developed for the simultaneous detection of Rhizopus oryzae, Rhizopus microsporus and the genus Mucor spp. in both culture and clinical samples. The methodology used was Molecular beacon species-specific probes with an internal control. This multiplex real-time PCR (MRT-PCR) was tested in 22 cultured strains and 12 clinical samples from patients suffering from a proven mucormycosis. Results showed 100% specificity and a detection limit of 1 fg of DNA per microlitre of sample. The sensitivity was 100% for clinical cultured strains and for clinical samples containing species detected by the PCR assay. Other mucormycetes species were not detected in clinical samples. This technique can be useful for clinical diagnosis and further studies are warranted.