Ecology, biological characterization and development of an animal model for Enterobacter sakazakii

Abstract

Enterobacter sakazakii is an emerging foodborne pathogen which has been linked to a number of outbreaks associated with the consumption of powdered infant formula, especially in low-birth-weight and premature infants. Very little research has focused on molecular characterization of this organism and the mechanism(s) by which it causes disease in humans. In this study, a collection of 260 isolates of E. sakazakii were assessed by phenotypic and genotypic tests. The use of 16S rDNA analysis showed an 82% identity amongst the strains tested. Interestingly, 14 strains originally identified as E. sakazakii by phenotypic characterization, were found to be other species or genera. Among the molecular typing methods, pulsed-field gel electrophoresis was found to be more discriminatory than automated ribotyping. Furthermore, the theory that expressed human breast milk, if contaminated with E. sakazakii, would support E. sakazakii growth at 10, 23 and 37°C, was investigated. It was found that the intrinsically ascribed antimicrobial properties of breast milk do not appear to inhibit the growth of this foodborne pathogen in vitro. Lastly, we assessed six animal species to find an animal model that would be well suited to conduct further studies on the virulence of E. sakazakii infection. Young (chicks, gerbils, guinea pigs, pigs, rabbits) and neonatal (gerbils, rats) animals were orally challenged with E. sakazakii at a level of 109 cells. Of all the animal models tested, it appears that the neonatal gerbil may be most suitable for further studies.