<i>In vitro</i> Comparison of Anti-Biofilm Effects against Carbapenem-Resistant <i>Acinetobacter baumannii</i> : Imipenem, Colistin, Tigecycline, Rifampicin and Combinations

다국어 초록 (Multilingual Abstract)

<P><B>Background</B></P><P>Multi-drug resistant (MDR) <I>Acinetobacter baumannii</I> has emerged as one of the most important nosocomial pathogens. In addition to the diverse resistance mechanisms, some <I>A. baumannii</I> strains are known to have biofilm-producing capacity, thereby decreasing antibiotic effectiveness.</P><P><B>Materials and Methods</B></P><P>This study was designed to assess biofilm-producing capacity of three different MDR <I>A. baumannii</I> strains with diverse resistance mechanisms (OXA-51, IMP-1 and VIM-2 type β-lactamases), and intended to compare the effect of each antibiotic regimen (rifampicin, colistin, imipenem, tigecycline, rifampicin-imipenem and rifampicin-colistin) on mature <I>A. baumannii</I> biofilms using <I>in vitro</I> polystyrene plate biofilm assay.</P><P><B>Results</B></P><P>Among three MDR <I>A. baumannii</I> strains, only VIM-2 strain produced strong biofilm compared to the controls (optical density, 8.04 ± 2.16 vs. 0.49 ± 0.26). Regarding VIM-2 strains, none of imipenem, colistin and rifampicin reduced biofilm formation alone at MIC of each antibiotic agent (inhibition of biofilm synthesis, less than 30%). In comparison, tigecyclin (0.76 ± 0.23), imipenem-rifampicin (1.07 ± 0.31) and colistin-rifampicin (1.47 ± 0.54) showed a significant inhibition of biofilm synthesis compared to the positive controls at 48 hours after incubation (<I>P</I><0.01). Tigecycline inhibited biofilm formation even at the one fourth level of MIC (1.17 ± 0.21). Likewise, both imipenem and colistin were also effective even with the reduced concentrations when those were combined with rifampicin. Such biofilm-inhibiting effects with those antibiotic regimens sustained up to 96 hours after incubation.</P><P><B>Conclusion</B></P><P>Tigecycline, imipenem-rifampicin and colistin-rifampicin would be effective for the prevention or reduction of biofilm formation caused by <I>A. baumannii</I> strains.</P>