| Summary: | In recent years, some outbreaks of bacterial infection in neonatal intensive care units have been traced to powdered infant formula contaminated with Cronobacter species, causing life-threatening diseases such as necrotizing enterocolitis and meningitis. This study for the first time presents growth data and whole genome comparisons for five different species of Cronobacter after the taxonomic revision by Iversen et al. (2008). Growth data for 28 bacterial strains across 21 bacterial species in casein- and whey-dominant infant formula at temperatures 21, 27, 37, 41 and 44oC were determined, covering category A and B organisms as defined by WHO 2006. The data revealed potential of some Cronobacter species to grow at 44oC, posing a significant risk of infection by the bacterium when following the current formula preparation guidelines. The results were presented to the Food Standards Agency with the aim to update the current risk assessment model and improve infant formula preparation guidelines. The first sequenced Cronobacter genome (C. sakazakii BAA-894) was used to construct a 384,030 probe oligonucleotide tiling DNA microarray covering its 4 Mb chromosome and plasmids pESA2 (31 kb) and pESA3 (131 kb). Comparative genomic hybridization (CGH) was undertaken on five C. sakazakii strains, and representatives of four other Cronobacter species. CGH highlighted 15 clusters of genes that were divergent or absent in more than half of the tested strains. Six of these were of probable prophage origin; other regions included type VI secretion systems, the O-antigen gene locus, a tellurite resistance cluster, a fimbriae cluster, and a copper resistance operon cop. The CGH analysis highlighted the role of horizontal gene transfer, as a significant part of the variable gene pool was due to acquisition of mobile DNA. A number of genes unique to Cronobacter species associated with neonatal infections (C. sakazakii, C. malonaticus and C. turicensis) were identified. These included a copper and silver resistance operon cus linked to invasion of the blood-brain barrier by neonatal meningitic strains of Escherichia coli. By comparing the neonatal intensive care unit outbreak strains with less virulent strains and by analysis of the variable regions, we identified a list of putative virulence factors that may improve our limited understanding of Cronobacter’ s pathogenesis.
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