Tehran University Medical Journal

Methods: The excretory-secretory and somatic antigens of two species were prepared from adult flukes collected from the bile ducts of sheep and stored at -20^oC. For the preparation of the antisera, the antigens were injected to laboratory-bred rabbits. Each rabbit received five injections at intervals of seven days, starting with 0.5 ml and ending with 2.5 ml. Ten days after the last injection, the rabbits were bled, and serum samples separated and stored at -20^oC. The reaction between homologous and heterologous antigens and antisera was tested by ELISA and optical densities were recorded.

Results: Excretory- secretory and somatic antigens of each species showed a strong positive reaction with the antisera of the other species. In a homologous combination of antigens and antisera, a stronger reaction was observed compared to the heterologous combination, therefore many antigenic materials of both species are the same.

Conclusion: The differences of these crude antigenic materials of F. hepatica and F. gigantica are insufficient to prevent cross reaction of two species by ELISA. Further investigations are recommended for the identification, detection and purification of antigenic material of each species to improve the specificity of this assay.

Background: The clinical importance of yeast infections has increased in recent decades. There are 10-15 pathogenic Candida species. The current morphological and physiological methods for identification of Candida species are generally not easy to interpret and may be expensive or time-consuming. In the present study, we introduce and use a new approach for the identification and differentiation of medically important yeast species of Candida. In this method, size polymorphism of the internal transcribed spacer regions, ITS1 and ITS2, of the ribosomal DNA in various Candida species is used as the basis of species recognition.

Methods: The genomic DNA of 31 standard strains and 60 clinical isolates was extracted and PCR-amplified using two primer pairs (ITS1-ITS2 and ITS3-ITS4) separately. Both PCR products were mixed and analyzed after standard agarose gel electrophoresis. The species of the tested yeasts were identified by the electrophoretic patterns of the mixed PCR products of each sample, comparing the data obtained from the sequence analyses of ITS1 and ITS2 molecules.

Results: By this method, with the exception of C. albicans and C. dubliniensis, we were able to clearly differentiate nearly all common pathogenic Candida species, including C. albicans, C. glabrata, C. gulliermondii, C. parapsilosis, C. tropicalis,      C. krusei, C. kefyr, C. lusinaniae and C. rugosa. All standard and clinical strains were identified correctly, without expensive methods such as sequencing and capillary electrophoresis.

Conclusion: It seems that the PCR-FSP method introduced in this study is the easiest molecular approach for the identification of a wide range of pathogenic Candida species and is applicable for diagnostic and epidemiological purposes in reference laboratories.