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j.m. miranda, c.m. franco, b.i. vázquez, c.a. fente, j. barros-velázquez and a. cepeda. 2005. To investigate the productivity and specificity of a new chromogenic enterococci selective medium (Chromocult® enterococci agar) recently developed by Merck. The study was carried out comparing Chromocult® enterococci agar with MRS agar (Merck), a basal lactic acid bacteria medium in current use. A total of 216 faecal samples from poultry were collected and enterococci populations were counted. Likewise, 100 randomly selected strains were identified for each medium. The differences found between the two media were analysed and discussed. A good sensitivity of 98% was obtained for Chromocult® agar and all false-positive isolates obtained were identified as Leuconostoc spp. However significant differences ( P < 0·01) were obtained between the enterococci species isolation rates identified from these two media, suggesting the poor growth of some species in Chromocult® enterococci agar. Viable counts of Enterococcus spp. obtained with MRS agar were significantly higher than those obtained with Chromocult® enterococci agar. The use of chromogenic media for microbiological analysis is increasing. Independent studies are important to evaluate newly developed chromogenic media. [ABSTRACT FROM AUTHOR]