Staphylococcus saprophyticus, a coagulase-negative staphylococcus (CNS), causes acute urinary tract infection predominantly in young women (15-30 years). In the clinical microbiology laboratory identification and differentiation of S. saprophyticus from other CNS usually depends solely upon the demonstration of resistance to the antimicrobial agent novobiocin. Phenotypic characteristics of 36 novobiocin-resistant CNS isolated from the urine of patients with acute urinary tract infections were further analysed and the homogeneity of the isolates assessed. The organisms were speciated by the API STAPH identification system. Twenty-one isolates were S. saprophyticus (p > 97%), and there was one strain each of S. epidermidis, S. hominis and S. simulans (p > 97%). Of the remainder, three isolates were unidentifiable and a further nine had the characteristics associated with more than one species of CNS. Additional tests, including carbohydrate fermentation, antibiotic sensitivity and fluorogenic substrate utilisation, were performed on all isolates. Computer analysis of the results confirmed that testing for resistance to novobiocin selects a heterogeneous group of CNS composed of several different species.
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