Comparative evaluation of five chromogenic media for detection, enumeration and identification of urinary tract pathogens

Five chromogenic agar plates - CPS ID2 medium (bioMerieux, France), CHROMagar Orientation medium (Becton Dickinson, France), UriSelect3 medium (Sanofi Diagnostics Pasteur, France), Rainbow Agar UTI medium (Biolog, USA) and Chromogenic UTI medium (Oxoid, Germany) - for the detection, enumeration and direct identification of urinary tract pathogens were compared using 443 urine specimens at two hospital laboratories. The enumeration of microorganisms was consistent on the five media for 403 of the 477 (84.5%) microorganisms. Chromogenic UTI, CPS ID2, UriSelect3, CHROMagar Orientation and Rainbow UTI gave detection rates of 98.3%, 97.9%, 97.3%, 96.9% and 94.1%, respectively, with some problems in yeast growth occurring on Rainbow UTI agar and problems in Staphylococcus spp, growth occurring on UriSelect3. For the direct identification of Escherichia coli, sensitivities were 93.8%, 88.5%, 86.1% and 82.2% for CHROMagar Orientation, CPS ID2, UriSelect3 and Rainbow UTI, respectively. Chromogenic UTI medium did not allow the accurate identification of Escherichia coli, since the indole reaction cannot be applied to this medium. Depending on the media, Enterococcus spp. could be identified at the genus or the species level. Slight differences were detected in the presumptive identification of the Proteus-Morganella-Providencia group and the Klebsiella-Enterobacter-Serratia group. Additionally, on Rainbow UTI agar, 12 of 20 Klebsiella Pneumoniae strains and two of nine Pseudomonas aeruginosa strains were correctly identified. In conclusion, CPS ID2 medium and CHROMagar Orientation medium showed similar performance overall, while the UriSelect3, Rainbow UTI and Chromogenic UTI media require some improvement.