Comparative Evaluation of Two Commercial Chromogenic Media for Detection and Presumptive Identification of Urinary Tract Pathogens

Abstract.

The performance of two commercial chromogenic media for the isolation and presumptive identification of urinary tract pathogens, the CPS ID2 (bioMérieux, France) and the CHROMagar Orientation (BBL Becton Dickinson, USA), was evaluated and compared with that of cystine-lactose-electrolyte-deficient agar and tryptic soy agar with 5% sheep blood. The detection, determination of bacterial counts, and presumptive identification of bacteria causing urinary tract infections were evaluated in 3,000 urine specimens. The two chromogenic media showed excellent correlation with the standard media for the detection and the bacterial count of urinary pathogens. The Escherichia coli strains produced the expected colour on the CHROMagar Orientation and the CPS ID2 media in 99% and 90% of the cases, respectively. The Klebsiella-Enterobacter-Citrobacter and the Proteus-Morganella-Providencia groups were easily identified on both chromogenic media, but further biochemical tests were needed to differentiate them to a species level. Both media enabled the differentiation, with varying degrees of difficulty, of Pseudomonas spp. strains from members of the family Enterobacteriaceae. All isolates of Enterococcus spp. were correctly identified and were easily distinguished from the Streptococcus agalactiae isolates. Staphylococcus saprophyticus isolates were easy to identify only on the CHROMagar Orientation medium. No substantial difference was observed when comparing the results of the susceptibility tests, which were performed according to the standardized disk diffusion method as described by the National Committee for Clinical Laboratory Standards, for colonies recovered from the blood agar versus those recovered from the chromogenic media. In conclusion, the CPS ID2 and CHROMagar Orientation media enabled excellent detection, count determination, and presumptive identification of urinary pathogens, both in pure and mixed cultures, and reliable and accurate antimicrobial susceptibility testing directly from primary isolates. Moreover, these media allowed a remarkable reduction in the workload and a significant savings of time. On the basis of their performance, these media can replace the standard primary plating media used in the routine diagnosis of urinary tract infections.