In Silico identification of pathogenic strains of Cronobacter from Biochemical data reveals association of inositol fermentation with pathogenicity

Abstract

BackgroundCronobacter, formerly known as Enterobacter sakazakii, is a food-borne pathogen known to cause neonatal meningitis, septicaemia and death. Current diagnostic tests for identification of Cronobacter do not differentiate between species, necessitating time consuming 16S rDNA gene sequencing or multilocus sequence typing (MLST). The organism is ubiquitous, being found in the environment and in a wide range of foods, although there is variation in pathogenicity between Cronobacter isolates and between species. Therefore to be able to differentiate between the pathogenic and non-pathogenic strains is of interest to the food industry and regulators.ResultsHere we report the use of Expectation Maximization clustering to categorise 98 strains of Cronobacter as pathogenic or non-pathogenic based on biochemical test results from standard diagnostic test kits. Pathogenicity of a strain was postulated on the basis of either pathogenic symptoms associated with strain source or corresponding MLST sequence types, allowing the clusters to be labelled as containing either pathogenic or non-pathogenic strains. The resulting clusters gave good differentiation of strains into pathogenic and non-pathogenic groups, corresponding well to isolate source and MLST sequence type. The results also revealed a potential association between pathogenicity and inositol fermentation. An investigation of the genomes of Cronobacter sakazakii and C. turicensis revealed the gene for inositol monophosphatase is associated with putative virulence factors in pathogenic strains of Cronobacter.ConclusionsWe demonstrated a computational approach allowing existing diagnostic kits to be used to identify pathogenic strains of Cronobacter. The resulting clusters correlated well with MLST sequence types and revealed new information about the pathogenicity of Cronobacter species.

Pan-genome analysis of the emerging foodborne pathogen Cronobacterspp. suggests a species-level bidirectional divergence driven by niche adaptation

“…The distribution of these operons and genes were in complete agreement with the biochemical results and species description reported by Iversen et al [1]. Inositol fermentation has recently been proposed as a marker of pathogenicity for Cronobacter , based on the presence of the inositol monophosphatase gene ( suhB ) in pathogenic strains [32]. In this study, we found that this gene, which is seemingly ubiquitous and highly conserved among the Enterobacteriaceae , is a component of the Cronobacter core genome (Additional file 1: Table S1).…”

Flagella from Five Cronobacter Species Induce Pro-Inflammatory Cytokines in Macrophage Derivatives from Human Monocytes

“…This strain was isolated from powdered formula and it was associated with a clinical outbreak, while the ST4 strain was primarily associated with infant formula and meningitis infection [12]. Although the source of C. sakazakii ATCC 29004 (used in this study) is unknown, clustering of the dominance of the meningitis-related strains in a single ST (ST4) and inositol fermentation in this clustering, allowed for the association to a pathogenic isolate [6], [49]. Interestingly, our data showed no significant differences during the pro-inflammatory cytokine activation in macrophages in the presence of flagella from both strains (ST1 and ST4).…”

“…Recently, Hamby et al , classified Cronobacter strains into two groups, pathogenic and non-pathogenic strains, observing an association between the source of the isolate, MLST type sequence (ST4) and inositol fermentation of the pathogenic strain [49]. The main sequence type identified in all strains of Cronobacter species analyzed by this method (383 isolated from Cronobacter distributed in 131 sequence types by MLST database) was ST4 corresponding to the C. sakazakii cluster [6], [12], [49]. Taking advantage of the diversity across the genus, we analyzed the ability of C. sakazakii sequence types ST1 and ST4 to induce anti- and pro-inflammatory cytokine release.…”

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

“…These authors and others also suggest that the virulence of Cronobacter spp. is dose-dependent, but not due to a property of a particular bacterial species as a whole, rather a characteristic(s) of certain strains, which may be innocuous in a full-term, yet pathogenic in a pre-term infant (Hamby et al, 2011;Cetinkaya et al, 2013). In vitro models of infection also suggest that the organism may also gain entrance into the systemic circulation through transcytosis of the GIT epithelium (Giri et al, 2012).…”