Antimicrobial susceptibility of 157 Gram-negative bacilli (90 Escherichia coli. 30 Enterobacter aerogenes, 18 Klebsiella pneumoniae, 12 Proteus spp., 3 Pseudomonas aeruginosa and 4 Alcaligenes faecalis) isolated from infected bovine udders was determined by the plate dilution method.
Gentamicin and oxolinic acid at a concentration of 12.5㎍/㎖ were very active to all of 157 Gram-negative bacilli tested, and 98% of these strains were susceptible to nalidixic acid at a concentration of 25μug/㎖. Most of the 90 Escherichia coli strains were inhibited by chloramphenicol, ampicillin and carbenicillin and carbenicillin at a concentration of 12.5㎍/㎖. None of the Klebsiella pneumoniae strains were inhibited at a concentration of 50㎍/㎖ of ampicillin and carbenillin, whereas all the species of Proteus resisted a concentration of 50㎍/㎖ or higher tetracycline. All the 3 strains of Pseudomonas aeruginosa were highly resistant to streptomycin, kanamycin, Ampicillin, chloramphenicol, tetracycline and nalidixic acid.
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