INDUCTION OF PROTECTION AGAINST ORAL INFECTION WITH CYTOTOXIN-PRODUCING ESCHERICHIA-COLI O157-H7 IN MICE BY SHIGA-LIKE TOXIN LIPOSOME CONJUGATE

We have previously reported that purified Shiga-like toxins (SLT), SLT -I and SLT-II coupled with liposomes induced a substantial amount of a nti-SLT-I and anti-SLT-II IgG antibody production, respectively, in mi ce. The levels of anti-SLT antibody in the sera of SLT-liposome-immune mice correlated well with the protection against subsequent challenge with SLT, In this study, mice were immunized intraperitoneally with t he mixture of SLT-I-liposome and SLT-II-liposome and protection agains t, oral infection with cytotoxin-producing Escherichia coli O157:H7 wa s evaluated. All of the mice that received immunization with the mixtu re of SLT-I-liposome and SLT-II-liposome were protected against subseq uent intravenous challenge with 10 LD50 Of either SLT-I or SLT-II, Eig ht weeks after primary immunization, mice were inoculated intragastric ally with 10(9) CFU of E, coli O157:H7 strain 96-60. All SLT-liposome- immune mice tested survived without any apparent symptom while control mice died within 5 days. In addition, as shown by other antigen-lipos ome conjugates, SLT-liposome induced undetectable anti-SLT IgE antibod y production while they induced substantial amounts of anti-SLT IgG an tibodies. These results suggest that SLT-liposome conjugate may serve as a candidate vaccine that induces protection against cytotoxin-produ cing E, coli infection.