Background: A. baumannii outbreaks are difficult to control because of the relative ease with which this microorganism spreads and persists in hospital settings. Successive papers reported increased resistance in clinical isolates of A. baumannii, currently resistant to most antibiotics. The purpose of this study was to characterize the epidemiological relationship and the mechanisms of resistance to several antimicrobial agents of a collection of A. baumannii strains. Material/Methods: Twenty A. baumannii isolated from two intensive care units (ICUs) at the Instituto Autónomo Universitario de Los Andes, Mérida, Venezuela, were analyzed by PFGE. Characterization of resistance determinants to various antimicrobial agents was also carried out. Results: PFGE typing revealed five different patterns. Pattern 1, susceptible to ciprofloxacin and cefepime, was found to be spread among the patients of both ICUs and was also cultured from a humidifier in the neonatal ICU. All the strains were resistant to gentamicin and tetracycline, 90% to amikacin and cefotaxime, and 85% to ciprofloxacin. The resistance of the strains to ceftazidime, cefepime, and imipenem was 40, 50, and 10%, respectively. All the strains showed β-lactamases with Ips equal to 5.4 (TEM-1) and greater than 9. Furthermore, two of them, both exhibiting resistance to imipenem, presented a β-lactamase with an Ip of 7.2 (OXA-58). Three of seven amikacin-resistant A. baumannii strains (PFGE-2) carried the gene encoding the APH(3′)-VIa enzyme and two strains (PFGE-5) had the TET(B) determinant. Conclusions: This study shows the dissemination of A. baumannii clinical isolates, a humidifier being the source of the strain. © Med Sci Monit, 2007.