Abstract
Cronobacter sakazakii is a food-borne pathogen carried in milk powder that can cause severe bacteremia, enterocolitis, and meningitis in newborns, which can lead to death of newborns. Preventing infection by this pathogen is significant to the health of newborns. Since infants and young children are the main target group of C. sakazakii, it is considered that maternal immunity can enhance the protection of newborns. Previous studies showed that two proteins of C. sakazakii (GroEL and OmpX) exhibited high expression levels and elicited strong immune reactions, suggesting their potential as vaccine candidates. In this study, GroEL and OmpX were recombinantly expressed in Escherichia coli and purified as immunogens to immunize pregnant rats. Three days after birth, the progeny were challenged with C. sakazakii to determine the protective effect of maternal immunity on the offspring. The results showed that immunization during pregnancy decreased bacterial load in the brain and blood, reduced brain and intestine damage, and significantly increased specific antibody titers in the offspring. Immunization with the recombinant proteins significantly increased cytokine levels in the serum of the progeny. The group whose mothers were immunized with OmpX produced more IL-4, while the group whose mothers were immunized with GroEL produced more IFN-γ, indicating that the immunogens enhanced the Th2 and Th1 responses, respectively. However, although the immune response was induced by both proteins, only the offspring of the pregnant rats immunized with OmpX or OmpX/GroEL mixture showed delayed death, possibly because immunization with OmpX led to a stronger humoral immune response in the offspring, suggesting that OmpX was a better vaccine candidate than GroEL. This study first reported that exposure to C. sakazakii proteins during pregnancy could improve the offspring's ability to resist infection caused by this pathogen.
Highlights
Cronobacter spp., previously known as Enterobacter sakazakii, are gram-negative, rod-shaped, motile, facultative anaerobic bacteria (Farmer et al, 1980)
The full-length genes of GroEL and OmpX were amplified from the genomic DNA of C. sakazakii ATCC 29544 and ligated into the pET-26b(+) vector to construct recombinant plasmids
SDS-PAGE analysis showed that GroEL and OmpX were well-expressed when the cells were induced by 0.05 mM IPTG
Summary
Cronobacter spp., previously known as Enterobacter sakazakii, are gram-negative, rod-shaped, motile, facultative anaerobic bacteria (Farmer et al, 1980) They are a group of opportunistic pathogens that primarily infect people with low immunity, such as infants and young children (Feeney et al, 2014). Maternal immune-derived cytokines have been proved to play an important part in the early defense against infection and immune regulation in progeny (Elahi et al, 2017). These studies provide a useful reference to improve resistance to C. sakazakii infections in newborns. This study provides a possible strategy to help infants resist the damage caused by C. sakazakii infection
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