An in silico analysis of osmotolerance in the emerging gastrointestinal pathogenCronobacter sakazakii

Abstract

Up to 80% of infants infected with Cronobacter sakazakii die within days of birth, making this emerging gastrointestinal pathogen a serious cause for concern. The mode of transmission most often associated with C. sakazakii infection is powdered infant formula (PIF), which typically has a water activity (aw) of ca 0.2--inhospitable to most bacterial pathogens. In the current study a comparative genomic approach was used to investigate the distinctive ability of this pathogen to survive and persist in such low aW conditions. A comprehensive review of the mechanisms involved in bacterial osmoadaptation was followed by an exhaustive homology transfer based approach to identify putative osmotolerance loci in the C. sakazakii genome. In total 53 osmotoleance loci were identified, including both hyper- and hypo-osmotic stress response systems, helping to construct a concise overview of the C. sakazakii osmotolerance response. Interestingly, while C. sakazakii contains homologues of all the principal osmotolerance loci of Escherichia coli; a key difference is that C. sakazakii contains multiple copies of certain osmotolerance loci; including seven copies of the E. coli proP homologue and two copies of OpuC--a multi component carnitine uptake system associated with Listeria monocytogenes and which has also been found to transport other compatible solutes such as glycine betaine, proline, ectoine and choline. Furthermore, the osmotic stress response of C. sakazakii appears to be regulated at the transcriptional, translational and post-translational levels, with RpoS most likely functioning as the global transcriptional regulator of the osmotolerance response.

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

“…Cronobacter are considered more resistant to dry and osmotic stresses than other members of the Enterobacteriaceae (Feeney & Sleator, 2011). It is thought that this is probably due to the accumulation of trehalose inside the cells, which works as a protectant (Breeuwer et al, 2003).…”

“…Another explanation was offered by , who showed that Cronobacter were recoverable from PIF even after 2.5 years, assuming that their extracellular polysaccharides could protect the cells against the desiccation effects. Furthermore, Feeney & Sleator (2011) showed bioinformatically that C. sakazakii contained multiple copies of the osmotolerance homologues ProP and OpuC, and they concluded that the osmotic stress response of C. sakazakii appears to be regulated at the transcriptional, translational and post-translational levels, with RpoS most likely functioning as the global transcriptional regulator of the osmotolerance response. Gurtler & Beuchat (2007) reported that the reduction in the viability of Cronobacter in PIF was less evident in formulas with water activity (a w ) values 0.25-0.30 compared with formulas with a w 50.43-0.50.…”

Cronobacter sakazakii: stress survival and virulence potential in an opportunistic foodborne pathogen

“…67 However, experimental data have demonstrated that this substitution has an effect on the mobility of the macromolecule and further research is needed to determine the mechanism of stabilization by trehalose. 68 The existence of a trehalose biosynthesis pathway in C. sakazakii is demonstrated by the presence of a putative otsBA operon 54 ; suggesting that the mechanism of trehalose biosynthesis in C. sakazakii is similar to that of E. coli. Furthermore, in addition to trehalose, other potentially important C. sakazakii compatible solutes include proline, betaine and ectoine, accumulated via secondary transporters homologous to the ProP porter in E. coli.…”

“…54 While homologues of all the principal E. coli osmotolerance loci were identified in the BAA-894 genome; multiple copies of certain osmotolerance loci; including 7 copies of the E. coli proP homolog were found. The ProP protein encoded by the gene locus tag ESA_02131 encodes a protein with 90% identity to E. coli ProP.…”

“…54 Most microorganisms require an a w significantly higher than that of PIF for growth and survival, suggesting that C. sakazakii is armed with a vast array of osmotic stress survival mechanisms. 54 However, the growth phase of the organism has also been demonstrated to play a role in C. sakazakii osmotolerance, with stationary phase cells demonstrating a higher resistance to osmotic and dry stress in comparison to other known osmotolerant organisms such as E. coli and Salmonella. 44 Further elucidation of C. sakazakii osmotolerance is aided by the wealth of knowledge available on how other bacterial cells overcome hyperosmotic stress and it is believed that C. sakazakii responds in a similar way.…”