The mechanism of bactericidal action of normal human serum against Salmonella rods.

Forty Salmonella strains sensitive to the bactericidal action of serum were investigated. All these strains were susceptible to complement activated by the classical pathway though in part (60%) of these strains the presence of lysozyme was necessary for killing. S. typhimurium rods were susceptible to only one mechanism of the action of bactericidal factors. On the contrary, S. enteritidis strains were sensitive to three various mechanisms of bactericidal action of serum. Next eight forms of Salmonella typhimurium LT2 differing with respect to the structure of LPS were studied. Original strain was a smooth, form S, and remaining strains were various rough (R) forms such as Ra, Rb1, Rb2, Rc, Rd1, Rd2, Re. The S form was susceptible only to the complete human serum what means that all bactericidal factors of serum were needed for killing. Ra form was susceptible to two independent bactericidal mechanisms: complement (C) activated by the alternative pathway in the presence of lysozyme and C activated simultaneously by both bactericidal C pathways without the participation of lysozyme (al, ac). The next form, Rb1, besides the mechanism mentioned above was also susceptible to C activated by the classical pathway in the presence of lysozyme (al, ac, cl). Other forms (Rb2, Rc, Rd1, Rd2, Re) were susceptible to three mechanisms (al, ac, cl) as well as to C activated by the classical pathway without lysozyme (c). The mechanism (c) was weakly efficient against forms Rb2 and Rc and somewhat more efficient against Rd1 and Rd2 and the most efficient against Re.