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This study reclassifies Enterobacter sakazakii, an opportunistic pathogen causing neonatal infections, into a new genus Cronobacter comprising multiple distinct species. Using polyphasic taxonomic analysis including 16S rRNA sequencing, DNA-DNA hybridization, and biochemical testing, researchers demonstrated that what was previously considered a single species actually comprises at least five genomospecies. DNA-DNA hybridization values revealed that malonate-positive strains represented a distinct species rather than a subspecies. The authors propose five new species: Cronobacter sakazakii (type strain ATCC 29544T), C. malonaticus, C. turicensis, C. muytjensii, and C. dublinensis. Cronobacter dublinensis is further subdivided into three subspecies based on phenotypic differences and DNA relatedness: subsp. dublinensis, subsp. lausannensis, and subsp. lactaridi. Additionally, Cronobacter genomospecies 1 is designated as a provisional species based on two strains. The study identified fourteen variable biochemical characteristics, including utilization of specific carbon sources and indole production, that differentiate the proposed taxa. This reclassification provides a more accurate taxonomic framework for identifying these clinically significant bacteria.

Key findings

• Enterobacter sakazakii was reclassified into a new genus Cronobacter comprising at least five distinct genomospecies based on DNA-DNA hybridization and molecular analysis
• Cronobacter malonaticus was identified as a distinct species (not a subspecies) through DNA-DNA hybridization showing 95.6% relatedness within biogroups 5 and 9
• Cronobacter dublinensis was subdivided into three subspecies (dublinensis, lausannensis, and lactaridi) corresponding to Farmer's original biogroups 12, 10, and 6 respectively
• Fourteen biochemical characteristics including malonate utilization, indole production, and various carbon source utilizations differentiate the proposed species and subspecies