Method for in vitro conversion of rough strains of Pseudomonas aeruginosa to smooth strains

Rough and serologically nontypable strains of Pseudomonas aeruginosa were found to become smooth and typable in vitro when they were maintained in a soft agar containing 0.5% peptone in distilled water and the dried out agar cultures were replenished monthly with a similar peptone solution in distilled water. After about a year, all of the nine rough strains of P. aeruginosa maintained this way became smooth and typable, and their pigmentations also changed significantly. Some melanogenic strains became fluorescine producers, and some weakly chromogenic strains became strong producers of fluorescine and pyocyanin.