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Category: Food Microbiology
Cronobacter Species, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555819972/9781555819965.ch14-1.gif /docserver/preview/fulltext/10.1128/9781555819972/9781555819965.ch14-2.gifAbstract:
The genus Cronobacter currently consists of seven species, including Cronobacter sakazakii, C. malonaticus, C. turicensis, C. muytjensii, C. dublinensis, C. universalis, and C. condimenti. This genus is now regarded as an opportunistic group of pathogenic bacteria with remarkable versatility in their abilities to cause disease in humans. It is now realized that infections due to Cronobacter can affect susceptible individuals, including neonates, infants, and elderly individuals, and it continues to attract attention in national and international media. Cronobacter species are recognized as being considerably more ecologically widespread than was once thought, and they have been found to be associated with many low-water-activity foods and environments, including powdered infant formula (PIF) and follow-up formulas, as well as in filth and stable flies, PIF and milk powder production facilities, household environments, and water. Pathogen-specific virulence factors have been discovered that adversely affect a wide range of eukaryotic cell and host processes, including protein synthesis, cell division, and proinflammatory host responses. A variety of mobile genetic elements, such as plasmids, transposons, and pathogenicity islands, have been identified, and this genomic plasticity implies ongoing microevolution with the possible acquisition of new virulence factors that will undoubtedly complicate efforts to classify these organisms into various subgroups or into sharply delineated genomopathotypes. This chapter describes the dynamic nature of Cronobacter, which is a highly diverse, versatile, opportunistic pathogen that will continue to present challenges for the global food safety and public health communities in terms of diagnosis, treatment, and prevention of infections.
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Transmission electron photomicrograph of C. sakazakii strain BAA-894 negatively stained with 0.5% sodium phosphotungstate (pH 6.8) showing numerous peritrichous flagella. Bar, 0.5 µm.
Revised FDA Cronobacter isolation and detection method, adapted from chapter 29 of the Bacteriological Analytical Manual (https://www.fda.gov/Food/FoodScienceResearch/LaboratoryMethods/ucm289378.htm). BPW, buffered peptone water; PBS, phosphate-buffered saline; R&F, Enterobacter sakazakii plating medium.
Neighbor net (SplitsTree4) analysis of 126 Cronobacter and phylogenetically related strains which were generated from the microarray-based gene differences described by Tall et al. ( 83 ). The phylogenetic tree illustrates that the Cronobacter microarray could clearly separate the seven species of Cronobacter, with each species forming its own distinct cluster. C. sakazakii subclades are designated with roman numerals I through VII. The scale bar represents 0.01 base substitution per site. Reprinted from reference 83 with permission.
Phylogenetic analysis using the neighbor-joining algorithm of 34 Cronobacter, 10 Enterobacter, and eight Enterobacter-related genomes based on the alignment of SNPs from 300 orthologous genes as described by Stephan et al. ( 72 ). Clades are represented by roman numerals 1 through V. Clade I represents genomes from Cronobacter species. Clade II represents genomes from F. helveticus and F. pulveris strains. Clade III represents genomes from two E. cloacae strains and genomes from Citrobacter, Salmonella, Escherichia, and Klebsiella strains. Clade IV represents genomes from S. turicensis strains. Lastly, genomes from two Pantoea strains are represented in clade V. The scale bar represents 0.05 base substitution per site. Reprinted from reference 72 with permission.
Sequence alignment of Cronobacter plasmids pESA3 and pCTU1 produced with the Artemis comparison tool as described by Franco et al. ( 79 ) and showing regions of homology. In the middle section, the red color indicates significant nucleotide homology, as determined by BLASTn analysis, between pESA3 and pCTU1, and the location on each plasmid, for example, eit, iuc, parAB, and repA. White areas indicate regions or loci present on one plasmid and absent on the other, e.g., cpa, T6SS genes, and FHA genes. The sequence of pESA3 was modified by rejoining the repA gene at the 3′ end, which is split in the GenBank sequence (NCBI RefSeq accession no. NC_009780.1). pESA3 and pCTU1 (NCBI RefSeq accession no. NC_009780.1) possess molecular sizes of 131,196 and 138,339 kb and mean G+C contents of 56.85% and 56.05%, respectively. Selected genes or loci are shown in color as follows: eit, red; iuc, orange; parAB and repA, purple; integrase genes, black, and associated genes, white; cpa, teal; T6SS genes, blue; and FHA genes, brown. Reproduced from reference 79 with permission.
Typical phenotypic (biochemical) characteristics of Cronobacter species a
Summary of 181 Cronobacter genome characteristics a
Plasmidotype patterns observed for 801 Cronobacter isolates representative of the seven Cronobacter spp.