Dead salmonellae or their endotoxin accelerate the early course of a Salmonella infection in mice

The course of a Salmonella infection following a low intravenous dose of virulent organisms was studied in mice. Simultaneous administration of 10(4) S. typhimurium C5 together with c. 10(8) dead salmonellae caused a marked acceleration of early net bacterial growth in the liver and spleen, leading to a rapidly overwhelming infection. Administration of similar numbers of either Staphylococcus albus or Bacillus cereus had no effect, whereas 20 micrograms of S. typhimurium Boivin-type lipopolysaccharide (B-LPS) produced an effect similar to dead organisms; 1 microgram B-LPS had a significant infection-accelerating effect. Both B-LPS and Westphal-type endotoxin (W-LPS) could enhance a salmonella infection in LPS-responsive C3H/HeMg mice, whereas only B-LPS was effective in LPS non-responder C3H/HeJ mice, implying that the infection-enhancing effect of a large bolus of dead organisms may be due in part to its LPS content. The results show that the course of a Salmonella infection following administration of large numbers of salmonellae in mice is different from that of Salmonella infections arising from small inocula. The relevance of these results to studies on the possible intracellular location of salmonellae in vivo is discussed.