Mycopathologia 157: 29–36, 2004. © 2004 Kluwer Academic Publishers. Printed in the Netherlands. 29 Performance of selective and differential media in the primary isolation of yeasts from different biological samples Jaqueline Otero Silva 1,2 , Silvio Antônio Franceschini 3 , Marco Aur´ elio Sicchiroli Lavrador 4 & Regina C´ elia Candido 5 1 Instituto Adolfo Lutz, Laborat´ orio I de Ribeirão Preto, São Paulo, Brasil; 2 Departamento de Microbiologia- Faculdade de Ciências Agr´ arias e Veterin´ arias de Jaboticabal, Universidade do Estado de São Paulo, SP, Brasil; 3 Sistema Integrado de Sa´ ude da Universidade de São Paulo, Ribeirão Preto, SP, Brasil; 4 Departamento de F´ ısica e Qu´ ımica da Faculdade de Ciências Farmacêuticas de Ribeirão Preto, Universidade de São Paulo, SP, Brasil; 5 Departamento de An´ alises Cl´ ınicas, Toxicol´ ogicas e Bromatol´ ogicas da Faculdade de Ciências Farmacêuticas de Ribeirão Preto, Universidade de São Paulo, SP, Brasil Received 25 September 2002; accepted 26 March 2003 Abstract In view of the increase in yeast infections, especially polymicrobial ones, differential culture media have acquired increasing importance. The present study evaluated the Sabouraud chloramphenicol, Biggy agar, Pagano Levin agar and CHROMagar Candida media in terms of isolation, number of yeast colony forming units per plate, and inhibition of bacteria and filamentous fungi. To this end, we used 223 biological samples, including feces, and oral, vaginal and anal mucosae from 86 patients presenting or not symptoms of fungal infections. The four media did not differ significantly in terms of detection of yeast-positive cultures. The number of colony forming units per plate ranged from zero to 2.380, with a predominance of counts of 1 to 9 colonies per plate. No significant differences were observed among the four culture media in terms of number of colonies counted, for each kind of biological material. Fifteen species belonging to the genera Candida, Saccharomyces, Cryptococcus, Trichosporon and Rhodotorula were isolated, with C. albicans being the predominant species, followed by C. parapsilosis and R. rubra. CHROMagar Candida and Biggy agar were complementary in the isolation of the different species and favored a greater recovery of polymicrobial cultures. Pagano Levin agar isolated the smallest variety of species. Sabouraud chloramphenicol agar was the least effective in terms of bacterial inhibition and favored a greater development of filamentous fungi. The results suggest that more than one culture medium should be used for an adequate primary isolation. Keywords: Biggy agar, Candida, CHROMagar Candida, yeasts, culture media, Pagano Levin agar Introduction The incidence of mixed infections with multiple yeast species has been increasing, mainly due to the in- creased numbers of immunocompromised patients and to the use of broad-spectrum antibiotics [1, 2]. Al- though Candida albicans continues to be the yeast most frequently involved in pathological processes, the emergence of other species has been clearly demonstrated [3–6]. Yeasts grow in different culture media but their development is suppressed when they are present in cultures with a mixed bacterial population [7]. Sabouraud dextrose agar, proposed in 1894, still is the medium most frequently employed in the primary isolation of pathogenic fungi [7]. Although its low pH inhibits the development of many bacteria, en- terobacteria and Pseudomonas sp. proliferate rapidly, impairing the isolation of pathogenic fungi from bio- logical materials [8]. Antibiotics, stains and some salts