The use of CHROMagar Orientation as a primary isolation medium with presumptive identification for the routine...

The aim of the study was to compare the use of a novel differential culture medium CHROMagar, for both primary isolation and presumptive identificaton, with the method currently used in our laboratory for screening mid-stream-urine samples (MSU). Routine methods (RM) included blotting paper imprinting of all specimens and additional quantitative culture on cysteine lactose electrolyte-deficient agar (CLED) for selected samples together with Microbact 12E for further identification. The CHROMagar method (CH) relied on the use of blotting paper imprints, colonial colour and morphology on CHROMagar only. With respect to the 3390 MSU specimens examined, both methods yielded similar results in 3240, including > or = 87% of Escherichia coli, Pseudomonas spp., Staphylococcus spp., Proteus mirabilis/Morganella morganii and Enterobacter/Serratia/Klebsiella/Citrobacter spp. Of the 52 discordant identifications, yeasts were reported as staphylococci on CHROMagar in 10. The overall cost of materials per specimen was US$ 0.30 by RM and $ 0.24 by CH. It took about 3 min to perform each Microbact test. Thus, CHROMagar plus Gram stain and other simple bench tests gave results similar to those using our current method, but had the advantage of saving time and materials.