Recognition of Staphylococcus saprophyticus in urine cultures by screening colonies for production of phosphatase

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Abstract
Phenolphthalein diphosphate was incorporated into a primary blood agar medium for use in performing quantitative urine cultures. Phosphatase-negative staphylococci, such as S. saprophyticus, were differentiated from phosphatase-positive species, such as S. epidermidis, by spot testing colonies on filter paper saturated with 1 N NaOH. Phosphatase-positive colonies turned pink within seconds, and phosphatase-negative colonies showed no color. None of 55 S. saprophyticus isolates showed production of phosphatase on this medium. Of 193 consecutive coagulase-negative staphylococci isolated from the urine of 190 adolescent female patients, 84% were phosphatase positive, non-S. saprophyticus; 16% were phosphatase-negative and indicated S. saprophyticus (22), S. haemolyticus (4), S. simulans (2), S. warneri (1) and S. hominis (1). Phosphatase activity was variable in the other flora encountered in the urine cultures. Mixtures of phosphatase-positive and -negative organisms did not cause false-positive reactions.