Use of trehalose-mannitol-phosphatase agar to differentiate Staphylococcus epidermidis and Staphylococcus saprophyticus from other coagulase-negative staphylococci

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Abstract
Using a plate medium containing trehalose, mannitol and phenolphthalein diphosphate (TMPA), significant clinical isolates of S. epidermidis were differentiated by their lack of acid production in 18 h from other coagulase-negative staphylococci, with the results having a sensitivity of 100%, a specificity of 89.9% and a positive predictive value of 94.8%. With a Taxo A bacitracin disk, which differentiates Staphylococcus spp. from Micrococcus spp., no zone of inhibition was seen for 96% of all staphylococcal strains, with 5 of 26 strains of S. saprophyticus exhibiting zone diameters up to 10 mm. By using resistance to a 5-.mu.g novobiocin disk, S. saprophyticus were differentiated, with the results having a sensitivity of 100%, a specificity of 97.1% and a positive predictive value of 83.9% on TMPA. These 2 spp. represented 77.8% of coagulase-negative staphylococci isolated. Reference strains of Staphylococcus and Micrococcus spp. were differentiated by TMPA. The cost of TMPA was compared with that of another method. TMPA was found to offer an inexpensive, sensitive method for rapidly differentiating coagulase-negative Staphylococcus isolates.