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Abstract

Antimicrobial activity of gallium maltolate against intracellular Rhodococcus equi

Nicole A. Miller,* Ronald J. Martens, Noah D. Cohen, Jessica R. Harrington, Lawrence R. Bernstein

Equine Infectious Disease Laboratory, Large Animal Clinical Sciences, College of Veterinary Medicine and Biomedical Science, Texas A&M University. College Station, TX 77845-4475.Nicole Miller

Objective-To evaluate the effectiveness of gallium maltolate to suppress the growth or kill intracellular Rhodococcus equi.

Sample Population- J774A.1 murine macrophage–like cells.

Procedure-J774A.1 cells were propagated in minimal media containing 10% fresh-frozen horse serum, and plated in 24-well tissue culture plates.  Gallium maltolate (GaM) (10 or 50 µM) was added to principal cells overnight, prior to infection, and controls were untreated cells. Virulent R. equi (ATCC 33701) were opsonized with fresh-frozen horse serum and added to principal and control cells at multiplicity of infections (MOI) of 1:1. Following phagocytosis, extracellular R. equi were controlled by washing and the addition of gentamicin.  The J774A.1 cells were lysed and R. equi concentrations determined by quantitative culture at 0, 24, 48, and 72 hr.

Results- Both concentrations of GaM significantly reduced the concentration of R, equi in cells relative to control cells at 48 hr.  At 72 hr, all groups differed significantly, in a dose-response manner.

Conclusions and Clinical Relevance-Results indicate that GaM inhibits growth or kills R. equi located within macrophages; thereby, suggesting its potential usefulness for the prevention or treatment of R. equi infections.