PHENOTYPICAL AND GENOTYPIC CHARACTERIZATION OF EPIDEMIC CLUMPING FACTOR-NEGATIVE, OXACILLIN-RESISTANT STAPHYLOCOCCUS-AUREUS

A total of 50 oxacillin-resistant Staphylococcus aureus (ORSA) strains that were clumping factor negative (CFN) and protein A negative by la tex agglutination were collected from patients in six different hospit als at different locations in Germany during 1991 and 1992. Antibiogra ms, bacteriophage typing, and plasmid analysis were performed. The ant ibiograms showed that, besides oxacillin, all CFN ORSA strains were re sistant to gentamicin, clindamycin, erythromycin, ciprofloxacin, and f osfomycin. All these isolates were nontypeable with an international s et of phages, and an additional experimental phage set indicated that the strains were phage type 16, 192. Moreover, all isolates possessed a single plasmid of 30 kb, and restriction analysis of those plasmids revealed identical patterns. For genotyping, these 50 isolates were al so analyzed by pulsed-field gel electrophoresis (PFGE) and polymerase chain reaction (PCR) of the coagulase and protein A genes and then by restriction enzyme digestion and analysis of restriction fragment leng th polymorphisms (RFLPs). With 49 strains, electrophoresis of SmaI-dig ested chromosomal DNA revealed identical PFGE patterns regarding the n umber and size of the DNA fragments, which could be differentiated fro m those of clumping factor-positive ORSA strains. Typing for the coagu lase gene by PCR revealed PCR products of identical sizes. The AluI re striction digestion patterns of the PCR products were identical. PCR w ith primers derived from the region of that part of the protein A gene that encodes the immunoglobulin G-binding domains showed a PCR produc t that was about 170 bp smaller than that of the protein A gene from s trains that were positive in the protein A latex agglutination test. S ince it is precisely this size that is required in order to encode one immunoglobulin G-binding region, we assume that this is not present i n the CFN ORSA strains. The phenotypical and genotypical features iden tify these very unusual CFN ORSA strains as being of clonal origin.