Characterization of Acinetobacter baumannii genotypes recovered from patients with repeated colonization or infection.

Acinetobacter baumannii has become an important nosocomial pathogen associated with increasing prevalence of multidrug resistance. Effective strategies to prevent emerging and spreading multidrug-resistant A. baumannii have not been well developed because of limited understanding of the organism epidemiology. The aim of this study was to determine if infection/colonization with A. baumannii after the initial isolation of the organism was due to the persistence of identical strain in patients with repeated positive clinical cultures. Forty-one patients with two or more clinical isolations of A. baumannii separated by at least 30 days were identified. The genotype of the first isolate from each patient was compared with the pulsed-field gel electrophoresis types of subsequent isolates of the same patient. Persistence of a single strain was detected in 51% patients. In the remaining 49% patients, subsequent isolates were not identical to the first isolate. Patients with isolates initially identified as carbapenem (imipenem or meropenem) resistant were 5.2 times more likely to have closely related isolates obtained for all subsequent cultures than patients with initial carbapenem-intermediate or carbapenem-susceptible isolates.