An in silico analysis of osmotolerance in the emerging gastrointestinal pathogen Cronobacter sakazakii.

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.