VIRULENCE AND BACTERIAL INFECTION 



mechanisms before definitive and final statements can be made 

 concerning this problem. 



SUMMARY 



Mice maintained in individual compartments without bedding 

 following infection with an avirulent strain of either Salmonella 

 t3^himurium or Staphylococcus aureus are more susceptible when 

 exposed continuously to 5° C thanthey are when exposed to 15° C or 

 to 25° C. These differences are not observed when virulent strains 

 are used, while acclimatization to cold for two weeks fails to alter 

 the response to the avirulent organisms. Mice kept at 5° C after in- 

 jection are sensitized 250-fold to pasteurized S. typhimurium and 

 about 10- fold to lipopolysaccharide derived from Serratia mar- 

 cescens compared to control animals housed at 25° C. Mice given 

 an LDyc dose of lipopolysaccharide and placed at 5° C for 12 hours 

 before transfer to 25° C areas susceptible to the endotoxin as mice 

 kept continuously in the cold. Conversely, mice given the same dose 

 and retained at 25° C for 6 or 12 hours before placing them at 5° C 

 are almost as resistant as mice kept continuously at 25° C. The 

 period of sensitization to lipopolysaccharide following cold exposure 

 was paralleled by the time at which a drop in body temperature 

 occurred following the low temperature stress and/or endotoxin 

 poisoning. 



Protection was afforded the cold exposed mice against endotoxin 

 poisoning by exogenously administered cortisone acetate, while 8 

 units of ACTH enhanced the lethal effects of the toxin. The adrenal 

 response of the host to temperature stress seems to be of para- 

 mount significance in determining the sensitization to lipopolysac- 

 charide. 



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