Plasmid DNA profiles of Acinetobacter baumannii: clinical application in a complex endemic setting

Abstract

Objective: To study the epidemiological, microbiological, and clinical features of infections due to Acinetobacter baumannii in a complex endemic situation over an 18-month period and to determine the clinical usefulness of plasmid DNA analysis of A baumannii in epidemiological investigations.

Design: Review of medical and laboratory records. Antibiotic resistance patterns, biotyping, and plasmid profile analysis were used to characterize clinical and environmental isolates. Pulsed-field gel electrophoresis (PFGE) of chromosomal DNA was performed to verify results obtained with the other typing methods.

Setting: Four different intensive care units of an 800-bed tertiary care center in Cologne, Germany.

Results: 240 patients were colonized or infected with A baumannii during the study period. No seasonal variations were observed. The majority of isolates (53%) were recovered from the respiratory tract. Major infections occurred in 61 patients; these included 48 bacteremias and eight pulmonary infections. Five different epidemic strains were identified: one each was A baumannii biotype 2 and 6, and three were biotype 9. A baumannii biotype 9 accounted for the vast majority of isolates (88%), which were clustered into three epidemic strains demonstrating distinct plasmid profiles. Two of these were considered genetically related as shown by PFGE. Epidemic strains were multidrug resistant, being uniformly susceptible to imipenem only. An epidemiological investigation failed to identify any point source of infection. Barrier precautions and improved handwashing was instituted in three of the four units and significantly reduced the incidence of colonization and infection in these units. Attack rates remained unchanged, however, in the burns unit where control measures were not implemented.

Conclusion: Acinetobacter strains representing multiple biotypes and plasmid types were present in this endemic setting. Multidrug resistance in A baumannii is an important concern. Plasmid DNA analysis proved to be useful in epidemiological typing of A baumannii strains and may serve as a complementary typing system to traditional epidemiological methods.