Abstract
BackgroundEnterobacter sakazakii is an opportunistic pathogen that has been associated with sporadic cases and outbreaks causing meningitis, necrotizing enterocolitis and sepsis especially in neonates. However, up to now little is known about the mechanisms of pathogenicity in E. sakazakii. A necessary state in the successful colonization, establishment and ultimately production of disease by microbial pathogens is the ability to adhere to host surfaces such as mucous membranes, gastric and intestinal epithelial or endothelial tissue.This study examined for the first time the adherence ability of 50 E. sakazakii strains to the two epithelial cell lines HEp-2 and Caco-2, as well as the brain microvascular endothelial cell line HBMEC. Furthermore, the effects of bacterial culture conditions on the adherence behaviour were investigated. An attempt was made to characterize the factors involved in adherence.ResultsTwo distinctive adherence patterns, a diffuse adhesion and the formation of localized clusters of bacteria on the cell surface could be distinguished on all three cell lines. In some strains, a mixture of both patterns was observed. Adherence was maximal during late exponential phase, and increased with higher MOI. The adhesion capacity of E. sakazakii to HBMEC cells was affected by the addition of blood to the bacteria growth medium. Mannose, hemagglutination, trypsin digestion experiments and transmission electron microscopy suggested that the adhesion of E. sakazakii to the epithelial and endothelial cells is mainly non-fimbrial based.ConclusionAdherence experiments show heterogeneity within different E. sakazakii strains. In agreement with studies on E. cloacae, we found no relationship between the adhesive capacities in E. sakazakii and the eventual production of specific fimbriae. Further studies will have to be carried out in order to determine the adhesin(s) involved in the interaction of E. sakazakii with cells and to enhance knowledge of the pathogenesis of E. sakazakii infection.
Highlights
Enterobacter sakazakii is an opportunistic pathogen that has been associated with sporadic cases and outbreaks causing meningitis, necrotizing enterocolitis and sepsis especially in neonates
In agreement with studies on E. cloacae, we found no relationship between the adhesive capacities in E. sakazakii and the eventual production of specific fimbriae
E. sakazakii has been isolated from a wide variety of foods, including cheese, meat, vegetables, grains, herbs, spices and ultra high heated milk [13,14,15], the bulk of research has been concentrated on the presence of the organism in milk-based powdered infant formula [12,16]
Summary
Enterobacter sakazakii is an opportunistic pathogen that has been associated with sporadic cases and outbreaks causing meningitis, necrotizing enterocolitis and sepsis especially in neonates. A necessary state in the successful colonization, establishment and production of disease by microbial pathogens is the ability to adhere to host surfaces such as mucous membranes, gastric and intestinal epithelial or endothelial tissue. Enterobacter (E.) sakazakii is considered a food borne pathogen that can cause severe illness and death in newborns, in prematures or infants with weakened immune system [1,2]. Pathogenesis involves bacteraemia and/or sepsis, cerebro spinal fluid infection and meningitis, intracerebral infarctions, brain abscess or cyst formation, and has been associated with necrotizing enterocolitis (NEC) [3,4,5,6,7]. A positive correlation between NEC and oral formula feeding has been suggested [12,13]
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