Effects of macrolide antibiotics against mucoid Pseudomonas aeruginosa

: Macrolide antibiotics at concentrations by far lower than their MICs proved to inhibit the production of alginate, elastase, and protease by mucoid Pseudomonas aeruginosa. The morphological study of mucoid P. aeruginosa under the electron microscope revealed the slime-like structures common to the cell morphology of the organism in cultured colonies and foci in a model for respiratory tract infection in mice, and the strains of mucoid P. aeruginosa which had been allowed to get in contact with the drugs proved to produced obviously fewer slime-like structures than control strains. The effect of a 14-membered macrolide, erythromycin, against mucoid P. aeruginosa was also observed with a 16-membered macrolide, rokitamycin this effect appeared to be common to the macrolide.