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Variations in properties of L-forms of Pseudomonas aeruginosa

In a study of the pathogenic potentials of Pseudomonas L-forms, three unstable L-forms were derived by carbenicillin inductionfrom a mouse virulent strain of Pseudomonas aeruginosa, Rosenthal 180. One L-form, induced on a sucrose-stabilized medium, grew more slowly and differed in a number of properties from two other L-forms induced on a medium supported with polyvinylpyrilidone. After adaptation to a common liquid medium, the three L-forms differed with respect to colonial shape on solid medium, growth rate, certain biochemical properties, antibiotic sensitivities and antigenic surface, and virulence for mice. The L-form may revert in vitro to a serotype different from that of the parent culture. The revertant may acquire new antibiotic resistances and sensitivities in the absence of previous exposure to the drugs and enhanced resistance to the L-inducing agent. The three L-forms showed a characteristically lower, but wide, range of virulence than did the parental form. Though death of mice was accompanied by reversion of the L-forms in vivo to the bacterial form, reversion in vivo was not necessary for virulence of L-forms. Modification of residual cell wall antigens accompanied the induction of each L-form as determined by type-specific antisera.