Outbreak caused by two multi-resistant Acinetobacter baumannii clones in a burns unit: emergence of resistance to imipenem.

Since early 1992 an increased number of tobramycin- and imipenem-resistant Acinetobacter spp. were observed causing colonization, wound infections, and bacteraemias in a burns and plastic surgery unit. This raised the question of whether this outbreak was caused by a single or by multiple Acinetobacter spp. clones. To study this, 97 Acinetobacter spp. isolates from clinical samples from different hospital units as well as isolates from the environment and the hands of the staff were characterized by antibiogram, plasmid profile and ribotyping. Two dominant multi-resistant A. baumannii clones were identified; one of them was sensitive to polymyxin B only. There was a close correlation between the results obtained by plasmid profiling and ribotyping. No common environmental source or significant hand carriage, or spread of these strains outside the unit were detected. The burns patients were the most likely reservoir, and strain transmission occurred in spite of strict control measures.