Comparison of ribotyping and pulsed-field gel electrophoresis for molecular typing of Acinetobacter isolates

Seventy-three isolates of the Acinetobacter calcoaceticus-Acinetobacter baumannii complex, including 26 isolates from 10 hospital outbreaks, were typed by ribotyping with EcoRI and ClaI and by pulsed-field gel electrophoresis (PFGE) of genomic DNA after digestion with ApaI. Ribotyping with EcoRI distinguished 31 ribopatterns. Digestion with ClaI generated another eight ribotypes. PFGE, in contrast, identified 49 distinct patterns with seven variants. Both methods detected all outbreak-related isolates. By ribotyping, nine epidemiologically unrelated strains could not be differentiated from outbreak strains, in contrast to only one isolate not identified by PFGE. Thus, PFGE was more discriminating than ribotyping. However, ribotyping is known to generate banding patterns specific to each DNA group in the A. calcoaceticus-A. baumannii complex that may be used for taxonomic identification of the strains. PFGE was shown to lack this property. Both methods are therefore useful for strain differentiation in epidemiological studies of Acinetobacter isolates.