Norepinephrine stimulates in vitro growth but does not increase pathogenicity of Salmonella choleraesuis in an in vivo model

Norepinephrine stimulates growth of Escherichia coil, Yersinia enterocoliti ca, and Pseudomonas aeruginosa in serum-supplemented media, and in vivo inc reases in norepinephrine may be important in the pathogenesis of sepsis by gram-negative bacteria. Because salmonellosis often is associated with stre ss, the effects of norepinephrine on in vitro growth, and in vivo pathogeni city of the swine pathogen Salmonella choleraesuis were investigated. When RPMI 1640 with and without pig serum was inoculated with fewer than 100 S. choleraesuis/ml and incubated overnight, bacterial numbers were 10(4) to 10 (6) lower in RPMI containing serum. Norepinephrine restored bacterial growt h in RPMI with serum to normal levels, but it did not increase growth in se rum-free RPMI. Similar results were obtained with SAPI, a nutrient-poor med ium previously used to study the effect of norepinephrine on growth of gram -negative bacteria. Conditioned media were produced by growing S. choleraes uis in RPMI containing serum with and without norepinephrine and filter ste rilizing. Conditioned medium produced with norepinephrine stimulated growth of S. choleraesuis but not E. coil, whereas conditioned medium produced wi thout norepinephrine stimulated growth of both bacteria. To determine the i n vivo effects of norepinephrine, rats were implanted with tablets that sec rete norepinephrine for 20 to 24 hours or with identical tablets without no repinephrine and infected intraperitoneally with graded doses of S. cholera esuis. The LD-50 of S. choleraesuis was the same in both groups, and norepi nephrine did not affect the carrier rate at 30 days after infection. We con cluded that although norepinephrine stimulates in vitro growth of S. choler aesuis in serum-based media, the increase in norepinephrine levels in the p resent in vivo system was probably not sufficient to influence the pathogen esis of S. choleraesuis infection.