Mucosal priming of the murine immune system against enterohemorrhagic Escherichia coli O157:H7 using Lactococcus lactis expressing the type III secretion system protein EspB

Enterohemorrhagic Escherichia coli (EHEC), particularly E. coli serotype O157:H7, has been responsible for multiple human outbreaks of hemorrhagic colitis and hemolytic uremic syndrome worldwide. Humans become infected by direct or indirect contact with faeces of asymptomatic EHEC shedding ruminants. Currently there is no human or animal vaccine available against EHEC infection. EHEC use a type III secretion system (T3SS) to colonize the intestine and therefore eliciting mucosal immunity against T3SS proteins could be a potential vaccination strategy. To develop such a mucosal vaccine, EspB – a significant member of the T3SS – was intracellularly expressed in Lactococcus lactis (LL-EspB) and this strain was used to immunize BALB/c mice orally. Ten days post-immunization, no specific antibody response was detected in serum or faeces of immunized mice. However, statistically significant (P < 0.0001) levels of specific serum Ig and faecal IgA were detected after intraperitoneal boosting of the orally immunized mice with recombinant EspB. Our results show that oral administration of LL-EspB resulted in mucosal priming of BALB/c mice against the EHEC T3SS protein, EspB. Nevertheless, an optimized EspB expression in L. lactis may be required to improve the mucosal immune response.