[A method for testing susceptibility of Haemophilus influenzae to co-trimoxazole (author's transl)].

Various methods for determining the activity of co-trimoxazole against haemophilus influenzae have been compared. The results were cortically influenced by antagonistic substances in the medium. The content of p-aminobenzoeacid and thymidine in the medium should be as low as possible. The antagonistic influences are compensated by lysed horseblood, which contains thymidine-phosphorylase. Haeminchloride and nicotinamide adenine dinucleotide (NAD) are better growth-factors than other poorly defined preparations (Supplement C, Fil-des-Enrichment, Iso-VitaleX). For the determination of the minimal inhibition concentration (MIC) we propose the microtiter technique. Likewise a modified agar diffusion test can be recommended for screening purposes. Of the 143 haemophilus influenzae strains tested against co-trimoxazole 134 (94%) were sensitive.