[Influence of low level antibiotics on Pseudomonas aeruginosa].

Erythromycine (EM) and chrolamphenicol (CP), the inhibitors of protein synthesis, were quantitatively examined for the growth of Pseudomonas aeruginosa EA83 and its production of extracellular proteins. The minimal inhibitory concentration (MIC) of EM for the strain was higher than 100 micrograms/ml and that of CP was 100 micrograms/ml. The growth curve of EA83 was not influenced by adding 5 micrograms/ml of EM to the broth culture, but proteolytic activity and the total protein in the culture supernate went down to 60% of the control. Number of organisms in 20 hour culture was almost constant regardless of EM concentration ranging from 0 to 50 micrograms/ml, however, the suppression of proteolytic activity and total protein in the culture supernate was seen even at 1 micrograms/ml of EM concentration. The degree of suppression was inversely proportional to EM concentration. This phenomenon was also seen in the substitution of CP for EM. All extracellular proteins separated on SDS-PAGE decreased the amount as increasing EM in the culture media. These results suggested that EM inhibited the production of not only protease including elastase, but also any other extracellular proteins including well known pathogenic factors such as exotoxin A and phospholipase C.