Use of a ribosomal RNA gene probe for the epidemiological study of methicillin and ciprofloxacin resistant Staphylococcus aureus

Conventional bacteriophage typing was combined with ribotyping in the analysis of methicillin and ciprofloxacin resistant Staphylococcus aureus strains isolated in increasing frequency since the introduction of the new 4-quinolones as therapeutic agents in the Tel-Aviv Medical Center. Whole-cell DNA was digested with EcoRI and HindIII restriction endonucleases. Agarose gel electrophoresis, Southern blotting, and hybridization by biotinylated probe DNA coding for ribosomal RNA revealed 7 to 14 bands. Analysis of the patterns established a single DNA type in EcoRI as well as in HindIII digests for all strains except one. Control strains from other sources differed in their band patterns. Bacteriophage typing confirmed the results of DNA typing. Thus, the frequent occurrence of staphylococcal isolates resistant to 4-quinolones in the hospital was not due to mutational development of resistance in many strains, but to the spread of a resistant strain.