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Chapter 1 : Taxonomy and Physiology of Enterobacter sakazakii
Category: Applied and Industrial Microbiology
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The Enterobacter species, representing a large and heterogeneous group within the Enterobacteriaceae, have increasingly been identified as pathogens over the past several decades. 16S rRNA gene-based phylogenetic trees offer a useful advantage to compare both easily recognizable species from different genera as well as difficult-to-identify or noncultivable isolates from the environment. The between-cluster hybridization experiments yielded hybridization values that were above the postulated 70% value for the distinction of genetic species, indicating that strains from the four clusters belong to the Enterobacter sakazakii species. The assignment of E. sakazakii to the Enterobacter genus was supported by data from hsp60 sequences showing the highest level of similarities between the four clusters and Enterobacter species than for Citrobacter koseri and by phenotypic characteristics. Enterobacter species are straight rods, are motile by peritrichous flagella, are facultatively anaerobic, grow readily on laboratory media, and ferment glucose with the production of acid and gas. The susceptibility of E. sakazakii to antibiotics is of interest, because it has a direct impact on the effectiveness of the treatment of patients in the hospitals.
Neighbor-joining tree of E. sakazakii and related clinical and environmental isolates based on partial 16S rRNA gene (550 bp) sequences. Sequences were obtained from EMBL or were kindly provided by S. J. Forsythe. Alignment was performed by ClustalX 1.83. The phylogenetic tree was built using the K81 evolutionary model, a gamma parameter at 0.76, and the bioNJ algorithm, implemented in PAUP 40b10 software.
Maximum-likelihood tree of the Enterobacteriaceae, including strains of E. sakazakii and related Enterobacter species based on gyrB (1,192 bp) sequences. The phylogenetic tree was built using the K81 evolutionary model, a gamma parameter at 0.935, and a heuristic strategy with tree bisection reconnection (TBR) branch swapping.
Neighbor-joining tree of E. sakazakii and related species based on partial hsp60 (343 bp) sequences. The phylogenetic tree was built using the Tamura-Nei (TrN) evolutionary model, a gamma parameter at 0.6, and the bioNJ algorithm.
Survival of Enterobacteriaceae at 4°C (top) and 8°C (bottom) in brain heart infusion broth. Abbreviations: Es, E. sakazakii; Ec, Escherichia coli; Kp, Klebsiella pneumoniae; Se, Salmonella enterica serovar Enteritidis. All strains were in stationary phase, except for the Es 1387 exp strain, which was in exponentional phase.
DNA relatedness of E. sakazakii strains a
Percent similarity between the hsp60 sequences of E. sakazakii strains and other Enterobacter species and Citrobacter koseri
Biochemical characteristics of Citrobacter, Pantoea, Kluyvera, and Enterobacter a
Biochemical differentiation of Enterobacter species a