LAUSR

OBJECTIVES Achromobacter xylosoxidans is an emerging pathogen in cystic fibrosis (CF). Relatively little is known about its clinical impact and optimal management. In the present study, the in vitro bactericidal activities of meropenem, either alone or in combination with colistin, levofloxacin, or chloramphenicol, were assessed using A. xylosoxidans strains isolated from CF patients. The synergistic interactions of these combinations were also investigated. METHODS Minimal inhibitory concentrations were determined by microbroth dilution. Bactericidal and synergistic effects of the tested antibiotic combinations were assessed by using the time-kill curve technique. RESULTS Based on the time-kill curves, we found that meropenem-colistin combinations have bactericidal and synergistic activities for 24hours against A. xylosoxidans strains both at 1xMIC and 4xMIC. Although synergistic interactions were seen with meropenem-levofloxacin combinations, no bactericidal interactions were observed. Additionally, the meropenem-chloramphenicol combinations were found to be neither bactericidal nor synergistic. No antagonism was observed with any combination tested. CONCLUSIONS This study's findings could have important implications for empirical or combination antimicrobial therapy with tested antibiotics.