Genotypic diversity of imipenem resistant isolates of Acinetobacter baumannii in Spain.

ABSTRACT

OBJECTIVES: To investigate relevant clinical and microbiological features of Acinetobacter baumannii in Spanish hospitals and to establish the genotypic diversity of imipenem resistant isolates. MATERIAL AND METHODS: Seven Spanish hospitals collected 354 consecutive isolates that were subjected to antimicrobial susceptibility testing by standard methods. Further genetic analysis was determined by PFGE in a subset of 135 isolates from three hospitals selected because each of them presented high-, medium-, and low imipenem resistance rates. RESULTS: Most isolates were from males (61.9%), age >65 years (52.3%), admitted to ICU (35.6%), and isolated from the respiratory tract (31.1%). Rates of carbapenem- and sulbactam resistance were 44.9% and 39.9%, respectively. Colistin was active against multiresistant isolates. Rates of imipenem resistance varied according to individual hospital (average 43.8%; range 13.5%-85.0%), medical department (more prevalent in ICU), and clinical sample (higher in isolates from the respiratory tract). Of the 135 isolates studied by PFGE (64 of them imipenem-resistant), 115 (85.1%) were distributed among 14 clusters and 20 were unrelated. Of the imipenem-resistant isolates, 45 (70.3%) belonged to six clusters that also had imipenem- susceptible isolates; 14 constituted four exclusive clusters, and five were unrelated. CONCLUSIONS: Acquisition of imipenem resistance in A. baumannii is likely due to both clonal and non-clonal dissemination; resistance rates strongly vary between different hospitals and even between different hospital departments.