beta-Lactamase substrate profiles of coagulase-negative skin staphylococci from orthopaedic inpatients and staff members.

Three different beta-lactamase substrate profiles were identified in 95 isolates of coagulase-negative staphylococci (CNS), of 57 different phenotypes, from 16 orthopaedic inpatients and staff members in one ward, by applying a bacterial whole-cell assay based on the hydrolysis of cefazolin, cephaloridine and nitrocefin. The typability of the assay was 93%, and 91% of the CNS isolates could be classified. To assess the discrimination between the beta-lactamase profiles obtained in the whole-cell assay, beta-lactamase extracts from 19 of the CNS isolates were used for estimation of their relative beta-lactamase substrate affinity index (RSAI). The RSAI assay was able to type previously unclassifiable or nontypable isolates. Two of the profiles obtained with the whole-cell assay were similar to those of the Staphylococcus aureus controls producing A or D and B or C beta-lactamases respectively. The distribution of beta-lactamase substrate profiles among the CNS isolates indicated an efficient spread of these drug resistance genes.