The use of plasmid profile analysis and ribotyping for typing Acinetobacter baumannii isolates

Plasmid profiles were used to analyse 39 Acinetobacter baumannii isolates from 36 patients at three hospitals. The isolates were previously classified by biotyping and rDNA fingerprinting. Ribotyping was useful to establish the lineage of isolates and to confirm genospecies identification. Thirty-seven isolates (94·9%) contained plasmids. The variable number of plasmids with different molecular weights in each isolate enabled the identification of 13 profiles without the need for endonuclease digestion. Fifteen A. baumannii biotype 2 isolates of similar ribotype and antibiotype contained identical plasmids over a two-month outbreak at one hospital. Plasmid typing discriminated these isolates from sporadic A. baumannii isolates of close ribotype obtained from different hospitals. A few isolates of different lineage, however, showed similar plasmid profile. Our results suggest that plasmid typing is a practical method to assist infection control of nosocomial A. baumannii. A combination of plasmid typing and ribotyping is suggested to confirm genospecies classification and to identify strains against reference band profiles.