Tissue cages for study of experimental streptococcal infection in rabbits. I. Production of erythrogenic toxins in vivo

Complementation of a speA negative Streptococcus pyogenes with speA: effects on virulence and production of streptococcal pyrogenic exotoxin A

We have shown previously that an isogenic SPEA-negative Streptococcus pyogenes strain did not attenuate virulence in a murine model of necrotizing fasciitis. The aim of this study was to confirm that streptococcal pyrogenic exotoxin A (SPEA) is not crucial for streptococcal invasiveness in murine invasive infection. The SPEA-negative S. pyogenes (H326) was complemented with speA extra-chromosomally to create strain H361 which produced 2.2-fold more SPEA compared with the parental speA(+)wild-type (H305). The growth phase-regulated expression of SPEA in vitro was unaffected in this strain. Complementation with speA resulted in reduced virulence and bacterial counts in invasive murine infection. SPEA production was quantitated from muscle tissue of infected mice. However, H361 did not produce more SPEA than H305 in vivo. We conclude that SPEA does not play a key role in invasive murine streptococcal infection.

The role of nitric oxide in experimental murine sepsis due to pyrogenic exotoxin A-producing Streptococcus pyogenes

Nitric oxide (NO) produced by inducible NO synthase (iNOS) mediates hypotension in endotoxemia. In this study, NO induction by a toxin-producing Streptococcus pyogenes isolate, H250, and by recombinant streptococcal pyrogenic exotoxin A (rSPEA) has been examined, both in vitro and in vivo. Streptococcal supernatants, but not rSPEA, induce production of nitrite by murine macrophages when both are coincubated with gamma interferon. Intraperitoneal injection of rSPEA did not cause significant production of NO. However, an elevated level of nitrate in serum was detected in a model of streptococcal fasciitis due to live H250. iNOS was localized to Kupffer cells, hepatocytes, and renal tubular cells by immunostaining. Administration of a NOS inhibitor, N(G)-monomethyl-L-arginine (L-NMMA), reduced peak concentrations of nitrate in serum but did not affect survival. NO is induced by H250, both in vitro and in vivo, mainly via SPEA-independent mechanisms. In this model, iNOS is expressed predominantly in the liver. Furthermore, in this model L-NMMA is not protective.

Tissue cages for study of experimental streptococcal infection in rabbits. III. Influence of immunization with erythrogenic toxin type A (ET A) and its toxoid on subsequent infection with an ET A producing strain

Purified erythrogenic toxin type A (ET A) and the corresponding toxoid, prepared by formalin treatment, were used for the immunization of rabbits (200 micrograms per rabbit). The impact of anti-erythrogenic toxin and toxoid immunity was investigated under the conditions of experimental infection with the ET A-producing Streptococcus pyogenes strain SF 130 (type 1). Whereas non of the immunized rabbits (n = 14) died after infection, 40% of nonimmunized animals did not survive (Table 1). The increase of the spleen weight after infection was significantly smaller in the immunized groups (Table 2). The immunized rabbits responded after infection with a significantly lower increase of fever which did not exceed 0.8 degree C (2 degrees C in infected non-immunized animals). Humoral antibodies to ET A were detected after immunization by means of ELISA. The challenge infection acted as a booster leading to a further increase of antibodies. The antibodies were found to be neutralizing the nonspecific mitogenicity of ET A in vitro in relation to the antibody titer. Cell-mediated immunity was tested in the lymphocyte transformation reaction with peripheral lymphocytes. The nonspecific mitogenicity of ET A, ET B, ET C and Con A was pronounced after immunization, whereas the nonimmunized rabbits responded to these antigens to a lower degree. The toxoid was found to be nonmitogenic. The altogether higher lymphocyte stimulation was also observed using spleen lymphocytes of immunized animals after infection.

Tissue cages for study of experimental streptococcal infection in rabbits. II. Humoral and cell-mediated immune response to erythrogenic toxins

Infection of rabbits with erythrogenic toxin producing streptococcal strains caused a marked increase of humoral antibodies, which was detected by immunoprecipitation and ELISA. An antibody response directed towards the erythrogenic toxin type A was demonstrated by fused rocket immunoelectrophoresis. All toxinogenic reference strains produced ET type A under in vivo conditions despite that this toxin was not always demonstrated under in vitro conditions. The infection resulted in an increase of mitogenic response of peripheral lymphocytes to the initial nonspecific mitogenic erythrogenic toxins, whereas the Con A stimulation was depressed starting 14 days after infection and lasting during a period of 90 days. Since a normal antibody response was evoked, it seems likely that the T helper cell function was not affected.

The influence of penicillin on growth and morphology of Streptococcus pyogenes in vivo

The influence of penicillin (pc) on the growth, phagocytosis and killing of Streptococcus pyogenes was studied for an M protein positive (M+) and an M protein negative (M-) strain in vivo as well as in vitro. In vivo studies were based on a tissue cage model and the analyses were performed by CFU determinations and electron microscopic investigations. The M- strain was easily phagocytized with and without pc, but killing only occurred after pc treatment and thus the number of viable bacteria rapidly decreased under the influence of pc. M+ streptococci were not reduced in numbers by pc-treatment in vivo, but morphological changes and at high pc concentrations, phagocytosis could be seen. When this strain (M+) was cultivated in the absence of pc, the phagocytic cells were totally destroyed - a reaction that was prevented by penicillin. Variations in surface morphology of the two strains seem to influence the differences in sensitivity to penicillin, phagocytosis and killing.

Static and dynamic properties of tissue cage fluid in rabbits

The properties of tissue cage fluid in a steel net tissue cage model in rabbits were compared to those of serum by determination of the protein profile, the cell contents, and the pharmacokinetics of 125I albumin, 3H sucrose and 3H fusidic acid. The dominating serum proteins demonstrated by crossed immunoelectrophoresis were also detected in tissue cage fluid but at lower levels and at various ratios. The cell pattern gradually changed from an initial dominance of polymorphonuclear cells to lymphocytes during the five weeks following the subcutaneous implantation of the cages. The distribution of the highly protein-bound fusidic acid was markedly slower and the maximal tissue cage fluid level significantly lower than that of sucrose. Equilibrium of 125I albumin between serum and tissue cage fluid was slowly achieved during the following two weeks. The advantages and disadvantages of tissue cage models for studies of drug pharmacokinetics are discussed. The properties of tissue cage fluid and the possibility of repeated sampling make the model suitable for studies of experimental local infections. The influence of therapeutic agents and the host's response to the infectious process may also be elucidated.

Streptococcal growth and toxin production in vivo

Streptococcal growth in vivo was studied with inoculated micropore filter chambers which were implanted into the peritoneal cavities of mice. Eight of nine group A strains and one group B strain grew in vivo, achieving concentrations of 10(7) to 10(9) CFU/ml in the chambers. Experiments with the Richards strain showed that the number of viable organisms remained high at 5 and 8 weeks after infection. The use of specific inhibitors and appropriate toxin-negative strains demonstrated that both cytolytic toxins produced by group A streptococci, streptolysin S and streptolysin O, were present in the culture fluids harvested from the chambers. This finding represents the first evidence that streptolysin S is produced in vivo. The host response to streptococci growing in vivo was examined by following the increase in serum antistreptolysin O levels. The response was first detected 2 weeks after chamber implantation and appeared to be maximal after 5 weeks. In addition, the production of antibody to streptococcal cell surface antigens was demonstrated indirectly with fluorescein-labeled anti-mouse immunoglobulin G.