Experimental Pyelonephritis. X. Direct Injection of E. Coli Protoplasts into the Medulla of the Rabbit Kidney †

Previous studies have demonstrated that the renal medulla is more susceptible to bacterial infection than the cortex.' Although more than 100,000 organisms are usually required to produce infection when injected directly into the normal renal cortex, fewer than 10 are necessary in the medulla. Many factors contribute to the remarkable ease with which infection is initiated in the renal medulla. Among these are the anti-complementary effect of ammonia2" and the interference with phagocytosis which occurs in a hypertonic environment.' A feature which has received little consideration is that the renal medulla is theoretically well suited for the survival of protoplast forms of bacteria. A protoplast, or L-form, is a differently shaped bacterium. Its peculiar shape results from inhibition of cell wall synthesis which may be affected by the action of certain antibiotics or antibody, complement and lysozyme systems.`7 The spherical protoplast will inbibe water, swell, and finally explode in media isotonic to plasma, whereas it may persist and even multiply in hypertonic media. Removal of the inhibitor of cell wall synthesis permits the reversion of the protoplast to normal bacterial form. The formation of protoplasts has been demonstrated in vitro and in vivo"' and undoubtedly represents one means by which bacteria are destroyed in host tissues which are isotonic to plasma. The persistence of protoplasts in hypertonic media in sitro prompted the suggestion that these forms might also be able to survive in vivo in a hypertonic environment. The renal medulla has, in recent years, been found to provide such a hypertonic environment.