INHIBITION OF PLANT PATHOGENIC BACTERIA IN VITRO BY ANTIBIOTICS AND QUATERNARY AMMONIUM COMPOUNDS

Abstract

The bacteriostatic effect of certain antibiotics and quaternary ammonium compounds on representative genera and species of phytopathogenic bacteria has been studied. For Xanthomonas species aureomycin was the most potent agent with terramycin and polymyxin next; 0.1 to 0.05 p.p.m. aureomycin completely inhibited growth of most of the cultures at 24 hr. Terramycin was the most effective compound against Pseudomonas species followed by streptomycin and qureomycin; 0.2 to 0.1 p.p.m. terramycin inhibited growth of every culture tested with one exception. For Corynebacterium species aureomycin was most effective with neomycin and terramycin next, the activity of aureomycin varying from 0.4 to 0.05 p.p.m. Chloromycetin was the least effective of the antibiotics tested in the series of experiments. A comparision of the relative sensitivity of the three genera to a given antibiotic revealed that aureomycin and polymyxin were most effective on Xanithomonas, terramycin and streptomycin on Pseudomonas, and neomycin and chloromycetin on Corynecarotovora to polymyxin. the latter organism was generally more resistant to the antibiotics than the former. A number of other antibiotics and quaternaries: streptothricin, clavacin, gliotoxin, aspergillic acid, tyrothricin, penicillin, Roccal, Hyamine 1622, and compound L4-669 were also tested against strains of X. phaseoli and P> phaseolicola (agents of common and halo blight respectively of beans). None of these was as effective as aureomycin, polymyxin, streptomycin, or terramycin, the activity of the quaternaries being similar on the whole to that of chloromycetin.