Methods: Bacterial isolates used in this study included a collection from the Trauma Infectious Disease Outcome Study (n=12) and a reference strain of A. baumannii (ATCC 17978). Antimicrobial activity of gallium compounds against planktonic and biofilm bacteria was evaluated by performing broth microdilution assays in iron-limited medias, RPMI 1640 and 10% MHB-II. Microdilution assays consisted of exposing bacteria or formed 24 hour biofilms overnight to increasing concentrations (0.25-512 µM) of the gallium compounds in 96-well plates or individual wells of the Calgary Device. Concentrations reducing viability of planktonic and biofilm bacteria to 50% and 90% of the untreated control were reported as the minimum inhibitory concentration or biofilm eradication concentration 50 and 90 (MIC/MBEC50 and MIC/MBEC90) respectively.
Results: Median IC50 and IC90 for GaNO3 were 64µM/128µM in MHBII and 128µM/256µM in RPMI, whereas IC50 and IC90 for GaMP and GaPP were 1µM/2µM and 2µM/8µM respectively with no observable difference seen with different media. The MBEC50 and MBEC90 for GaNO3, GaMP, and GaPP were 256µM/512µM, 16µM/32µM, and 128µM/256µM respectively.
Conclusion: Gallium (III) compounds have differential activity against MDR A. baumannii in planktonic and biofilm forms. The heme-conjugated gallium compounds (GaMP/GaPP) had the most potent in vitro activity. Further investigations should explore their potential role as novel anti-biofilm agents.
K. S. Akers, None
J. Wenke, None
C. Sanchez Jr., None