Oral Immunization with Lactococcus lactis Expressing EspB Enhances Clearance of Escherichia coli O157:H7 in two Murine Infection Models

Enterohemorrhagic Escherichia coli (EHEC) have been responsible for outbreaks of hemorrhagic diarrhoea and the hemolytic-uremic syndrome (HUS) worldwide. HUS is the most common cause of acute renal failure in children and results in fatalities as high as 50% in the elderly. Currently, neither a specific treatment nor a vaccine is available for EHEC. Lactococcus lactis, a generally regarded as safe bacterium, was constructed to express the EHEC antigen, EspB. Different constructs either produced low cytoplasmic levels of EspB,  or secreted EspB constitutively or under nisin-induction. Oral immunization of mice with these constructs resulted in weak to strong responses, respectively, which were correlated with the amount of antigen produced. The EspB-secreting strains successfully induced EspB-specific mucosal and systemic antibodies as well as a mixed Th1/Th2 response with a predominance for Th2. The nisin-induced EspB secreting strain could significantly reduce the amount and/or duration of colonization of EHEC with more than 50 %. Our results demonstrate the protective potential of EspB and the efficient delivery of recombinant EspB by L. lactis in mice. In larger species the use of L. lactis will be mortgaged by its low survival in the harsh environment of the gut. We demonstrated the detrimental effect of bile and pancreas enzymes. The presence of aluminium hydroxide (a bile acid binder) and camostat mesylate (a trypsin inhibitor) could significantly improve survival in vitro and in vivo. In pigs a 38- and 24-fold increase in L. lactis-counts in jejunal and ileal contents of treated animals was obtained.