Abstract
Cronobacter sakazakii (C. sakazakii) is an emerging opportunistic foodborne pathogen that can cause neonatal necrotizing enterocolitis, meningitis, sepsis in neonates and infants with a relatively high mortality rate. Bacterial transcytosis across the human brain microvascular endothelial cells (HBMEC) is vital for C. sakazakii to induce neonatal meningitis. However, few studies focus on the mechanisms by which C. sakazakii translocates HBMEC. In this study, the translocation processes of C. sakazakii on HBMEC were explored. C. sakazakii strains could effectively adhere to, invade and intracellularly survive in HBMEC. The strain ATCC 29544 exhibited the highest translocation efficiency across HBMEC monolayer among four tested strains. Bacteria-contained intracellular endosomes were detected in C. sakazakii-infected HBMEC by a transmission electron microscope. Endocytosis-related proteins CD44, Rab5, Rab7, and LAMP2 were increased after infection, while the level of Cathepsin L did not change. C. sakazakii induced TLR4/NF-κB inflammatory signal pathway activation in HBMEC, with increased NO production and elevated mRNA levels of IL-8, IL-6, TNF-α, IL-1β, iNOS, and COX-2. C. sakazakii infection also caused LDH release, caspase-3 activation, and HBMEC apoptosis. Meanwhile, increased Dextran-FITC permeability and decreased trans epithelial electric resistance indicated that C. sakazakii disrupted tight junction of HBMEC monolayers, which was confirmed by the decreased levels of tight junction-related proteins ZO-1 and Occludin. These findings suggest that C. sakazakii induced intracellular bacterial endocytosis, stimulated inflammation and apoptosis, disrupted monolayer tight junction in HBMEC, which all together contribute to bacterial translocation.
Highlights
Cronobacter sakazakii (C. sakazakii) is rod-shaped Gramnegative opportunistic pathogen, which is closely associated with neonatal necrotizing enterocolitis, sepsis, meningitis, and meningo-encephalitis in neonates and infants (Mullane et al, 2007; Weng et al, 2014)
Four strains were efficiently translocated across the human brain microvascular endothelial cells (HBMEC) monolayers (Figure 1D)
Cronobacter sakazakii-contaminated powdered infant formulas have been associated with outbreaks of infant meningitis (Alzahrani et al, 2015)
Summary
Cronobacter sakazakii (C. sakazakii) is rod-shaped Gramnegative opportunistic pathogen, which is closely associated with neonatal necrotizing enterocolitis, sepsis, meningitis, and meningo-encephalitis in neonates and infants (Mullane et al, 2007; Weng et al, 2014). Cronobacter sakazakii is one of the important pathogens implicated in neonatal meningitis (Ogrodzki and Forsythe, 2015). Previous studies have shown that several meningitis-related pathogens could penetrate the blood brain barrier (BBB) and invade the central nervous system (CNS). To cause infections in the brain, the pathogen needs to survive in the host bloodstream, cross the BBB and gain entry into the CNS (Van Sorge and Doran, 2012). C. sakazakii has been proved to be able to invade epithelial and endothelial cells and evade the immune responses, thereby leading to bacterial colonization and proliferation in the host CNS to induce meningitis (Almajed and Forsythe, 2016)
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