Novel method for measuring growth of Treponema hyodysenteriae and its application for monitoring susceptibility of clinical isolates to antimicrobial agents.

A microdilution assay method was developed to determine MICs of antibiotics for Treponema hyodysenteriae and to estimate the bacterial burden of mice colonized by this swine pathogen. Hemolysis of bovine erythrocytes in broth was correlated with growth of the spirochete, and growth inhibition by drugs could be determined by measuring hemolysis. MICs of 10 antibiotics for eight clinical isolates of T. hyodysenteriae measured by this method were similar to values obtained by an agar dilution method and to values reported in the literature. This method was also used to demonstrate the elimination of T. hyodysenteriae from the ceca of infected mice following oral treatment with carbadox. The procedure described in this paper provides a rapid and simple method for determining MICs of antibiotics for T. hyodysenteriae and may be adapted for the purpose of determining the presence of this veterinary pathogen in cecal contents of experimentally infected mice.