A Rapid Method for Demonstrating the Action of Staphylococcus Enterotoxin upon Rana Pipiens *

Studies of staphylococcal food poisoning have been made difficult by the lack of an easy, reliable method for demonstrating the presence of an enterotoxin, elaborated by certain strains of Staphylococcus aureus (Micrococcus pyogenes). The commonly used laboratory animals (guinea pig, mouse, rabbit, rat) are rodents, which as a class lack the appropriate mechanism for vomiting. These animals, therefore, are valueless in this study since the presence of the enterotoxin in any substance is demonstrated by its ability to elicit a vomit reaction. At present, the usual method for the demonstration of the enterotoxin is to administer either the suspected foodstuff or a filtrate prepared from a strain of Staphylococcus aureus isolated from suspected food, to human volunteers, monkeys, kittens, or cats, all of which are known to possess the vomit mechanism. Slocumi has clearly summarized the limitations of these three tests, reporting that the use of human volunteers is not without danger, that monkeys are expensive and difficult to house, and that kittens and cats are most difficult to obtain and maintain in confinement. He further points out that each of these species not only shows variation in susceptibility to the enterotoxin, but also is capable of developing resistance to it upon repeated administration. The common frog, Rana pipiens, an inexpensive and readily available animal which is known to possess a vomit mechanism, was chosen for further study by Robinton.' It was shown that upon administration of a known staphylococcal enterotoxin, a physiological reaction was obtained, designated as a spasm, which was an outward manifestation of an antiperistaltic action of the stomach. This method, however, has proven of limited application because of the apparently uncontrollable time lapse between the administration of the enterotoxin and the occurrence of the spasm which indicates a positive reaction. Mellinger' reported that the frog was capable of vomiting by the action of the stomach alone without the aid of other structures. Upon administration