Proceedings of the 10th International Colloquium on Paratuberculosis

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#37 Antimicrobial activity <strong>of</strong> gallium nitrate against Mycobacterium avium subsp.
paratuberculosis (MAP) in vitro
Marie-Eve Fecteau, Raymond Sweeney, Robert Whitlock
University <strong>of</strong> Pennsylvania, USA
The objectives <strong>of</strong> this study were to evaluate <strong>the</strong> in vitro susceptibility <strong>of</strong> various virulent strains <strong>of</strong> MAP to gallium
nitrate (GaN), and to investigate <strong>the</strong> potential use <strong>of</strong> GaN as a prophylactic agent for <strong>the</strong> control <strong>of</strong> MAP
infections in cattle. Gallium, a trivalent semi-metal that shares many similarities with ferric iron and functions as
an iron mimic, has been shown to have antimicrobial activity against various microorganisms, including Rhodococcus
equi, Pseudomonas aeruginosa, and Mycobacterium tuberculosis.
The in vitro susceptibility <strong>of</strong> several virulent strains <strong>of</strong> MAP to GaN was tested using broth culture with
detection <strong>of</strong> MAP growth by a non-radiometric automated detection methodology, which employs fluorometric
detection <strong>of</strong> oxygen consumption. Ten different strains <strong>of</strong> MAP were used, including 4 cattle strains, 2 bison
strains, 1 alpaca strain, and 3 human strains. For each MAP strain, a series <strong>of</strong> 7 dilutions <strong>of</strong> GaN were tested,
ranging from 200µM/L to 1000µM/L concentrations. GaN was determined to have caused 99% inhibition <strong>of</strong>
<strong>the</strong> MAP growth at that GaN concentration where <strong>the</strong> time to detection <strong>of</strong> <strong>the</strong> MAP undiluted stock + GaN was
leng<strong>the</strong>ned to that <strong>of</strong> <strong>the</strong> 10-4 dilution <strong>of</strong> MAP without GaN.
All 10 MAP strains were susceptible to GaN. The susceptibility to GaN was variable between each isolate,
and was dose-dependent for all isolates. Overall, <strong>the</strong> 99% inhibition ranged from < 200µM/L for <strong>the</strong> most susceptible
strains to > 1000µM/L for <strong>the</strong> least susceptible strains. In general, <strong>the</strong> most susceptible strains were <strong>of</strong>
alpaca or bison origins, whereas <strong>the</strong> least susceptible strains were <strong>of</strong> human and bovine origins.
Gallium nitrate demonstrated antimicrobial activity against all 10 strains <strong>of</strong> MAP tested in vitro, and could
potentially be used as a prophylactic agent to aid in <strong>the</strong> control <strong>of</strong> MAP infections during <strong>the</strong> neonatal period.
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