STUDIES ON THE VIRULENCE OF A NATURALLY OCCURRING MUTANT OF SALMONELLA TYPHOSA

Abstract

A mouse virulent and a mouse avirulent strain of Salmonella typhosa. both isolated from the Panama Carrier, have different nutritional requirements. The strain virulent for mice requires cystine and tryptophane for growth, while its naturally occurring avirulent mutant requires a purine in addition. It has been shown that the peritoneal fluid of mice, which is the menstruum in which the challenge suspension must multiply initially, does not supply the nutritional requirements of purine deficient strains. The injn. of xanthine into the peritoneum of mice challenged with the avirulent, purine requiring mutant resulted in a significant increase in virulence of this strain. A reversion of the avirulent culture to purine independence was accompanied by a marked increase in virulence. These results obtained with a naturally occurring mutant substantiate the work of other investigators who have shown that nutritional factors as well as antigenic structure may play a dominant role in determining mouse virulence of certain bacterial cultures.