Studies on Escherichia coli vaccines: an in vitro approach to establishing safe limits of endotoxins in vaccines.

A total of fifty production batch samples from six different vaccines for pigs, sheep and cattle were monitored for their endotoxin content. All vaccines recommended for parenteral administration into pregnant animals were aqueous and cellular with the exception of one comprising enterotoxin only. The Limulus amoebocyte lysate test was used for endotoxin determination. Total endotoxin of the vaccine was estimated and a method has been devised to estimate the enterotoxin bound either to the cells or the adjuvant. The highest endotoxin levels obtained for pigs, sheep and cattle vaccines were 47.9 micrograms ml-1, 4.7 micrograms ml-1 and 2.4 micrograms ml-1 respectively. All these vaccines have been found to be safe in pregnant animals. The non-cellular vaccine containing enterotoxin only had an endotoxin level of 0.47 microgram ml-1.