Liliane Alves Scheid

Candida dubliniensis: Epidemiology and Phenotypic Methods for Identification

Candida dubliniensis is an emerging pathogen first described in 1995, which shares many phenotypic features with Candida albicans and therefore may be misidentified in microbial laboratories. Despite various phenotypic techniques described in the literature to differentiate the two species, the correct identification of C. dubliniensis remains problematic due to phenotypic similarities between these species. Thus, as the differences between both are best characterized at genetic levels, several molecular methods have been proposed to provide a specific and rapid identification of this species. Epidemiological studies have shown that C. dubliniensis is prevalent throughout the world and it is primarily associated with oral carriage and oropharyngeal infections in patients infected with human immunodeficiency virus (HIV). However, data acquired from its isolation from other healthy and immunocompromised patients are variable, and there is still no real consensus on the epidemiological relevance of this species. In this article, we review the various phenotypic methods used in the identification of C. dubliniensis and the epidemiological impact of this new species.

Enzymatic and hemolytic activities of Candida dubliniensis strains

Candida dubliniensis is an opportunistic yeast that has been recovered from several body sites in many populations; it is most often recovered from the oral cavities of human immunodeficiency virus-infected patients. Although extensive studies on epidemiology and phylogeny of C. dubliniensis have been performed, little is known about virulence factors such as exoenzymatic and hemolytic activities. In this study we compared proteinase, hyaluronidase, chondroitin sulphatase and hemolytic activities in 18 C. dubliniensis and 30 C. albicans strains isolated from AIDS patients. C. albicans isolates produced higher amounts of proteinase than C. dubliniensis (p < 0.05). All the tested C. dubliniensis strains expressed hyaluronidase and chondroitin sulphatase activities, but none of them were significantly different from those observed with C. albicans (p > 0.05). Hemolytic activity was affected by CaCl2; when this component was absent, we did not notice any significant difference between C. albicans and C. dubliniensis hemolytic activities. On the contrary, when we added 2.5 g% CaCl2, the hemolytic activity was reduced on C. dubliniensis and stimulated on C. albicans tested strains (p < 0.05).

In vitro activities of antifungal agents alone and in combination against fluconazole-susceptible and -resistant strains of Candida dubliniensis

In the present study we used two groups of Candida dubliniensis strains: one containing fluconazole-susceptible clinical isolates and another containing fluconazole-resistant laboratory derivative from the former to examine the changes on susceptibility accompanying the development of resistance to fluconazole. Our findings confirmed the ability of C. dubliniensis isolates to become resistant to fluconazole and indicated that this resistance was crossed with ketoconazole, itraconazole, ravuconazole and terbinafine. We also tested combinations of terbinafine, amphotericin B, itraconazole and voriconazole against both groups of isolates in a checkerboard assay. Surprisingly, most combinations evidenced indifferent interactions, and the best synergism appeared when terbinafine and itraconazole were combined against the fluconazole-resistant group.

Comparison among tomato juice agar with other three media for differentiation of Candida dubliniensis from Candida albicans

The purpose of the present study is to compare the tomato juice agar, a well known medium employed to observe ascospore formation, with niger seed agar, casein agar and sunflower seed agar, applied to a differentiation between C. dubliniensis and C. albicans. After 48 hours of incubation at 30 degrees C all 26 (100%) C. dubliniensis isolates tested produced chlamydospores on tomato juice agar as well as in the other three media evaluated. However, when we inoculated all media with C. albicans, the absence of chlamydospores became resulting in the following percents: tomato juice agar (92.47%), niger seed agar (96.7%), casein agar (91.39%), and sunflower seed agar (96.7%). These results indicate that tomato juice agar is another medium which can also be used in the first phenotypic differentiation between C. dubliniensis and C. albicans.

Differentiation of Candida dubliniensis from Candida albicans on rosemary extract agar and oregano extract agar

Candida dubliniensis is a recently described pathogenic species which shares many phenotypic features with Candida albicans and therefore, may be misidentified in microbiological laboratories. Because molecular methods can be onerous and unfeasible in routine mycological laboratories with restricted budgets such as those in developing countries, phenotypic techniques have been encouraged in the development of differential media for the presumptive identification of these species. We examined the colony morphology and chlamydospore production of 30 C. dubliniensis isolates and 100 C. albicans isolates on two new proposed media: rosemary (Rosmarinus officinalis) extract agar (REA) and oregano (Origanum vulgare) extract agar (OEA). These substrates are traditionally used as spices and medicinal herbs. In both of these media, all C. dubliniensis isolates (100%) showed rough colonies with peripheral hyphal fringes and abundant chlamydospores after 24 to 48 hr of incubation at 25°C. In contrast, under the same conditions, all isolates of C. albicans (100%) showed smooth colonies without hyphal fringes or chlamydospores. In conclusion, REA and OEA offer a simple, rapid, and inexpensive screening media for the differentiation of C. albicans and C. dubliniensis. J. Clin. Lab. Anal. 22:172–177, 2008.

Carbohydrate assimilation profiles of Brazilian Candida dubliniensis isolates based on ID 32C system

The purpose of the present study was to evaluate the identification of 19 Brazilian C. dubliniensis based on the biochemical profile exhibited when tested by the commercial identification kit ID 32C (bioMerieux). Thirteen of the isolates were rigorously identified as C. dubliniensis and the remaining isolates (six) were considered as having a doubtful profile but the software also suggested that there was 83.6% of chances for them to be C. dubliniensis. As well as pointed by the literature the identification obtained by phenotypic tests should be considered presumptive for C. dubliniensis due to variability of this new species.

Reavaliação da suscetibilidade de candida a anfotericina B : estudo comparativo com isolados de três hospitais do estado do Rio Grande do Sul

Susceptibility to amphotericin B was compared between isolates of Candida spp that were obtained from candidemia cases as follows: 41 from Hospital Universitario de Santa Maria, 56 from Hospital de Clinicas, Porto Alegre, and 47 from the Santa Casa hospital complex, Porto Alegre. The tests were based on the document M27-A2 from the Clinical Laboratory Standards Institute, but with 20 concentrations of amphotericin B ranging from 0.1 to 2mg/ml. The tests were carried out using RPMI 1640 medium with glucose, antibiotic medium 3 and yeast nitrogen base-dextrose. The antibiotic medium 3 broth generated wide ranges of minimum inhibitory concentrations and minimum fungicidal concentrations in relation to the other agents. The variations in susceptibility between the hospitals were best detected in antibiotic medium 3. The isolates from Hospital Universitario de Santa Maria showed lower susceptibility than did those from the Santa Casa hospital complex, Porto Alegre (p < 0.05). The causes of the susceptibility variations were not assessed but they indicate the need for surveillance regarding the susceptibility to amphotericin B.

Differentiation of Candida dubliniensis from Candida albicans with the use of killer toxins

The aim of this study was to report the ability of killer toxins, previously used as biotyping techniques, as a new tool to differentiate C. albicans from C. dubliniensis. The susceptibility of C. albicans and C. dubliniensis to killer toxins ranged from 33.9 to 93.3% and from 6.67 to 93.3%, respectively.

Novo meio seletivo-indicador para detecção de Aeromonas e Plesiomonas: ágar UNISC

We evaluated a new selective indicator medium (UNISC Agar) for isolation of classical enteropathogens, Aeromonas spp and Plesiomonas shigelloides. The xylose fermentation capacity is indicated by a yellow color (fermenting agents) or blue (no fermenting agent). This, together with the oxidase test, establishes it as an indicator for detecting Aeromonas and Plesiomonas shigelloides. Its productivity and selectivity, as assessed using the absolute count index and relative count index, indicate it as an alternative to the classical feces culturing media. This is because, in a single medium, it enables isolation of Escherichia coli, Shigella spp and Salmonella spp, in addition to Aeromonas and Plesiomonas shigelloides, thereby favoring the laboratory diagnosis of gastroenteritis.

ESTUDO EPIDEMIOLÓGICO E PERFIL DA SUSCETIBILIDADE DE AMOSTRAS DE CANDIDA ISOLADAS DE MULHERES COM CANDIDIASE VULVOVAGINAL EM FREDERICO WESTPHALEN – RS

As infeccoes causadas por Candida sao micoses oportunistas reconhecidas desde o seculo V a.C.O genero Candida e caracterizado como fungo leveduriforme, saprofita e oportunista, que sob determinadas condicoes multiplica-se, tornando-se patogenico. Celulas de Candida sao encontradas navagina em 20% de mulheres sadias e assintomaticas. A candidiase vaginal ocorre, principalmente,nas mulheres que estao entre a puberdade e a menopausa, sugerindo dependencia hormonal nainfeccao. No periodo de agosto de 2004 a junho de 2005 foram realizadas coletas de amostras desecrecoes vaginais de mulheres com sintomatologia de infeccao vulvovaginal atendidas em tresestabelecimentos de saude de Frederico Westphalen – RS. As amostras positivas foram identificadase a sensibilidade frente os antifungicos fluconazol e anfotericina B foi avaliada. Os resultados obtidos demonstram que Candida spp. ocupou o quarto lugar dentre todas as especies isoladas causando infeccoes vulvovaginais, sendo que a identificacao apontou Candida albicans como especiemais prevalentemente isolada. Os testes de suscetibilidade revelaram que Candida glabrata foimais sensivel do que Candida albicans e Candida tropicalis a anfotericina B. Frente ao fluconazolCandida albicans e Candida tropicalis foram consideradas sensiveis. De acordo com as normas doNCCLS os isolados foram considerados sensiveis a anfotericina B e fluconazol.