In-vitro effect of various antimicrobials in combination against multidrug-resistant acinetobacter baumannii

In recent years, Acinetobacter spp. have emerged as one of the most important nosocomial pathogens, especially in patients admitted to an intensive care unit (ICU). The progressively increasing resistance of A. baumannii to widely used antibiotics is now a major problem in our country like worldwide. Due to antibiotic resistance with Acinetobacter baumannii has increased and leads clinicians to find alternativeantibiotics.In this study, 50 Acinetobacter baumannii ( A. baumannii ) isolated from various clinical specimens from June 2005 to September 2009 in Celal Bayar Univesity, Faculty of Medicine, Departmant of Microbiolgy and Clinical Microbiolgy, Bacteriology Laboratory were investigated. Isolation and identification were performed by conventional biochemical tests as well as by BBL Crystal GN; N/F ID ( Becton Dickinson,USA) or Phoneix 100 BD systems (Becton Dickinson Microbiology Systems). The antibiotic susceptibilities of the strains were investigated by the disk diffusion method according to the recommendations of the CLSI.The present study aimed at evaluating the interaction between colistin/rifampicin, colistin/imipenem, tigecycline/rifampicin and tigecycline/imipenem through microdilution checkerboard and E-test method against ten MDR A. baumannii strains. The secondary objective was to examine the degree of agreement of a possible new method utilizing the E-test with the checkerboard method.According to our in-vitro study results, the checkerboard method with the combination regimens of colistin/rifampicin and colistin/imipenem each showed 80% synergistic activity. Due to colistin is not currently in use in our country, combinations of tigecycline/rifampicin could be promising alternatives for the treatment of infections due to MDR strains of A. baumannii.The agreement between the checkerboard tests and Etest method was 52.5% (range 10?70%). Further comparison studies of the E test synergy technique with the checkerboard and time-kill methods are warranted.