False-positive rabbit ileal loop reactions attributed to Vibrio parahaemolyticus broth filtrates

Vibrio parahaemolyticus broth filtrates have previously been shown to produce positive reactions in rabbit ileal loops only if concentrated 10-fold by lyophilization. This method of concentration produces solutions that contain greater than 20% NaCl. In the present study, however, concentrations of NaCl of greater than or equal to 4% induced positive responses in ileal loops, and desalting rendered previously reactive, concentrated broth filtrates negative. Therefore, enterotoxin was not demonstrated in our broth filtrates of V. parahaemolyticus, a finding which suggests that previous studies require further evaluation. Since most culture media contain 0.5% NaCl, it is important to determine and to control the NaCl content and the osmolality of all lyophilized concentrates tested in the ligated rabbit ileum.