Response of Six Strains of Eimeria brunetti to Two Antagonists of para-Aminobenzoic Acid

SYNOPSIS. Sulfaquinoxaline and ethopabate are 2 chemically distinct types of antagonist of PABA with anticoccidial action. Reversal experiments with PABA and synergism studies with pyrimethamine indicated that both compounds interfered with the PABA-folic acid metabolic sequence. Six pure strains of Eimeria brunetti responded differently to the 2 compounds. The strain most sensitive to ethopabate was one of 2 strains most resistant to sulfaquinoxaline. Conversely, the strain most sensitive to sulfaquinoxaline was unresponsive to the highest doses of ethopabate employed. Hypotheses to explain the differences in biological effects of the 2 compounds were considered.