THE EFFECT OF TEMPERATURE ON THE SYNTHESIS OF VIRULENCE FACTORS BY <i>PASTEURELLA PESTIS</i>

Abstract

Sokhey and Habbu reported in 1943l that the limiting temperatures for the growth of Paslewella peslis were -2" C. and +45" C. with an optimum growth temperature of 27" to 28°C.Since that time only a few publications have appeared correlating the growth temperature to the synthesis of factors that may be implicated in conferring maximal virulence.Meyer and his associates have indicated that the envelope or capsular substance designated as Fraction 1 (Fl), produced at 37" C., rendered P .pesfis resistant tophagocytosis.2Burrows and Bacon have reported that incubation a t 37" C. was necessary to render virulent P .peslis cultures previously grown a t 28" C. resistant to phagocytosis by mouse neutrophiles in the absence of demonstrable encapsulation and for the synthesis of V and W antigens that they associated with ~irulence.~A Fukui el al. have demonstrated that the virulence of cultures grown on agar slants a t 37" C. was usually greater than similar cultures grown a t 26" C.6 and was comparable in virulence to cultures grown in vivo (unpublished data).The results of subsequent studies comparing the virulence of cultures grown at 5" C., 26" C., and 37" C. revealed a direct correlation between the growth temperature and virulence.The virulence of cultures grown a t 5°C.was consistently depressed, but it could be fully restored during a short period of incubation at 37" C. in the absence of apparent cellular multiplication.