of these agents , 4 macrolides ( erythromycin , oleandomycin , kitasamycin , tylosin ) , 3 tetracyclines ( tetracycline , chlortetracycline , oxytetracycline ) , 1 peptide ( colistin ) , 1 penicillin ( ampicillin ) and 1 pleuromutilin ( tiamulin ) were the most active agents , showing a minimal inhibitory concentration of less than 0.39 micrograms/ml for more than 90 % of the isolates .
C0039651
tetracyclines
C0008293
chlortetracycline