Permeability factor-like skin reaction in rabbits induced by endotoxin of Salmonella sp.

An inflammatory skin reaction similar to the permeability factor (PF) described for the thermolabile (TL) enterotoxin of Escherichia coli was induced in rabbits inoculated intradermally with supernatants from cultures of Salmonella typhimurium and S. enteritidis. This PF-like activity was observed with both crude supernatants as well as those which were submitted to gel filtration through Sephadex G-100. PF-like activity was found only in fraction 1 (F1) of the chromatographed materials. It was resistant to boiling, proteolytic enzymes and wide variations of pH. Serological studies based on agglutination and immunodiffusion tests demonstrated that F1 materials were closely related to the somatic antigen of group B Salmonella. No specific TL activity, as detected by the Y-1 adrenal cell assay and the passive immune haemolysis test, could be demonstrated. Furthermore, F1 materials were not enterotoxigenic as assayed by the rabbit ileal loop assay, and no neutralization of PF-like activity could be obtained in tests carried out using F1 preparations pre-incubated with either anti-F1 or cholera antitoxin. Based upon these findings, it seems reasonable to suppose that most PF reactions, already reported as being caused by a TL-like enterotoxin produced by Salmonella, are probably due to endotoxin. In fact, this possibility was reinforced by the Sanarelli-Shwartzman phenomenon which was produced in rabbits inoculated with F1 materials.

Passive immune hemolysis for detection of heat-labile enterotoxin produced by Escherichia coli isolated from different sources.

Fifty-one strains of Escherichia coli isolated from humans, swine, food, and water and identified as enterotoxinogenic by the Y-1 adrenal cell assay, were examined for heat-labile enterotoxin (LT) production by the passive immune hemolysis test. Cholera antitoxin, anti-choleragenoid and anti-LT were used as antisera. Cholera antitoxin was much more potent than anti-choleragenoid and LT antiserum in the detection of LT-positive strains. All strains isolated from pigs and sausage were negative in tests made with LT antiserum. A few strains isolated from humans, food, and water also gave negative results. These data showed that the passive immune hemolysis test is not as efficient as the Y-1 adrenal cell assay in the detection of enterotoxinogenic E. coli strains.