On the diagnosis of coagulase-negative staphylococci with emphasis on Staphylococcus saprophyticus

This study concerns the diagnosis of coagulase-negative staphylococci, with special emphasis on novobiocin-resistant species, vis S. saprophyticus, S. cohnii and S. xylosus. Disc diffusion tests for novobiocin were found useful in the differential diagnosis of coagulase-negative staphylococci isolated from urine specimens, but not from pus and blood cultures. We report on the resistance of S. saprophyticus to nalidixic acid and the use of this characteristic in the diagnosis of coagulase-negative staphylococci known to be novobiocin-sensitive, but which have subsequently acquired resistance to novobiocin. The results of different tests for betalactamase production in S. saprophyticus are presented. "Clover leaf" tests suggested such a production in about half of the strains studied, while no strain produced betalactamase as indicated by tests using chromogenic cephalosporin or benzylpenicillin in capillary tube tests. -The failure of tests for nitrate reduction, glucose consumption and of cultrues of urine on MacConkey's agar in the diagnosis of urinary tract infections caused by S. saprophyticus, is documented. The concept "significant bacteriuria" in the diagnosis of S. saprophyticus infections of the urinary tract above the bladder neck is also considered.