Enterobacter sakazakii invades brain capillary endothelial cells, persists in human macrophages influencing cytokine secretion and induces severe brain pathology in the neonatal rat

Abstract

Enterobacter sakazakii is an opportunistic pathogen associated with contaminated powdered infant formula and a rare cause of Gram-negative sepsis that can develop into meningitis and brain abscess formation in neonates. Bacterial pathogenesis remains to be fully elucidated. In this study, the host inflammatory response was evaluated following intracranial inoculation of Ent. sakazakii into infant rats. Infiltrating macrophages and neutrophils composed multiple inflammatory foci and contained phagocytosed bacteria. Several genotypically distinct Ent. sakazakii strains (16S cluster groups 1-4) were shown to invade rat capillary endothelial brain cells (rBCEC4) in vitro. Further, the persistence of Ent. sakazakii in macrophages varied between strains. The presence of putative sod genes and SOD activity may influence the survival of acidic conditions and macrophage oxidase and contribute to Ent. sakazakii intracellular persistence. The influence of macrophage uptake of Ent. sakazakii on immunoregulatory cytokine expression was assessed by ELISA. This demonstrated that the IL-10/IL-12 ratio is high after 24 h. This is suggestive of a type 2 immune response which is inefficient in fighting intracellular infections. These findings may help explain how the diversity in virulence traits among Ent. sakazakii isolates and an unsuccessful immune response contribute to the opportunistic nature of this infection.

Cronobacter spp. – opportunistic food-borne pathogens. A review of their virulence and environmental-adaptive traits

“…Cronobacter appear to evade the host's immune system by adapting to a lifestyle of replication in the intracellular environment confined within macrophages. Townsend et al (2007b) showed that that Cronobacter can persist within human U937 macrophages and survival varied between strains, Cronobacter persisting intracellularly for up to 96 h. In another study, most Cronobacter strains persisted in macrophages for 48 h (Townsend et al, 2008). These results suggest that Cronobacter possess virulence properties that enable them to tolerate the intracellular environment of macrophages.…”

“…Kothary et al (2007) identified the gene locus of zinc-containing metalloprotease (zpx) -a protein that caused rounding of CHO cells in tissue culture. In addition, the presence of putative sodA genes might provide resistance for Cronobacter against intracellular macrophage oxidase and acidic conditions, and may contribute to its intracellular persistence (Townsend et al, 2007b). However, these genes and OmpA and OmpX were found in all Cronobacter spp., and thus cannot be responsible for the variation in pathogenicity among the different Cronobacter strains (Joseph et al, 2012c).…”

“…Superoxide dismutases are metalloenzymes that help bacteria resist intracellular oxidative stressed environments within the polymorphonuclear leukocytes (Townsend et al, 2007b). Additionally, overexpression of outer-membrane protease Cpa (plasminogen activator) was reported following the entry of Cronobacter systemically.…”

“…The fact that Cronobacter can exploit immature dendritic cells and persist within human macrophages indicates that Cronobacter possess some immune evasion properties that enable them to avoid the host's immune response, and reach and penetrate the blood-brain barrier (BBB) (Townsend et al, 2007b(Townsend et al, , 2008Mittal et al, 2009b;Emami et al, 2011;.…”

Insights into virulence factors determining the pathogenicity ofCronobacter sakazakii

“…The pathogen is reported to persist within human macrophages indicating that the Cronobacter possessed virulence properties that make it allows to tolerate the intracellular environment of macrophages. 124,125 Conclusions and future perspectives Cronobacter spp is a newly classified genus and more research is yet to be completed for better understanding this unique group of organism. As a virulent species, it causes high mortalities in the neonates, therefore, it is important to understand which gene products are responsible for the pathogenicity of the bacteria and how the expression of these virulence factors is regulated.…”