Resistance of free-living nematodes to staphylococcal enterotoxin.

The usefulness of free-living nematodes for assaying staphylococcal enterotoxin was evaluated with a 98% pure enterotoxin B on five different nematodes. Included in the evaluation was an enterotoxin B in a crude culture filtrate. The filtrate of a culture of nonenterotoxigenic strains of Staphylococcus aureus, the uninoculated respective broth media, and distilled water were used as controls. The purified enterotoxin was found to exert no toxic effects at dosages ranging from 10 to 1,000 mug/ml for as long as 24 hr. Utilization of the toxin-protein by these nematodes was evidenced by their propagation after exposure times longer than 24 hr. The crude filtrate, containing 28 mug of enterotoxin per ml, was detrimental to nematodes to the same degree as the nontoxic filtrate and the uninoculated broths, in that they all caused irritation to external genitalia, motility changes, and death after comparable exposure times. This is in agreement with earlier observations that standard bacteriological fluid media, or broths containing over 1% protein hydrolysate or 1 to 2% salts, exert toxic effects on free-living nematodes.