754 PROTECTION OF NEWBORN RATS FROM Kl E. COLI INFECTION

Abstract

We have shown previously that newborn rats develop sepsis/meningitis after i.p. injection of Kl E. coli. The present studies examine the effect of passive immunization on infection. Pregnant rats were immunized X2 by i.v. injection of formalin-killed E. coli (type 07:Kl:H?). Some members of subsequent litters were exchanged shortly after birth with pups from saline-immunized mothers. At age 5 days, all pups were challenged by i.p. injection of 1.2 × 10¹ CFU of a Kl E. coli strain (018ac:Kl:H7). Quantitative blood cultures were obtained daily. Of 29 pups born to and nursed by Kl-immunized dams, 34% and 41% had bacteremia 1 and 3 days later vs. 59% of 29 unexchanged pups from saline-immunized dams (p >0.05). Mortality rates were 38% (Kl) and 34% (controls) at 7 days. Exchanged animals had infection and mortality rates similar to the above. Since rat pups are able to absorb IgG (of different species) from the GI tract, other groups were given oral supplements of group B meningococcal horse serum (h.s.) which reacts with Kl antigen (Group I); normal h.s. (Group II); or water (Group III) for 2-4 days and challenged at 5 days of age. Three days later 54% of Group I had bacteremia vs. 60% of Groups II and III; however, mortality rates were 8%, 33% and 30%, respectively (p <0.05). Group I had initial bacteremia with geometric mean CFU/ml 1 log lower than that of Groups II and III.

This method of maternal immunization against Kl E. coli gave poor protection to rat pups. Oral feeds of anti-capsular anti-body favorably modified intensity of bacteremia and mortality.

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