Enterobacter sakazakii is the name proposed for the organism previously known as “yellow-pigmented Enterobacter cloacae.” The type strain (holotype) of this species is ATCC 29544. The proposed change in the classification of this organism is based on differences between E. cloacae and E. sakazakii in deoxyribonucleic acid (DNA)-DNA hybridization, biochemical reactions, pigment production, and antibiotic susceptibility. By DNA hybridization, E. sakazakii was about 50% related to E. cloacae, Citrobacter diversus (“Citrobacter intermedius” biotype b), and “Citrobacter amalonaticus” (“Citrobacter intermedius” biotype a). The new species was placed in Enterobacter rather than Citrobacter because of its closer phenotypic and DNA similarity to E. cloacae, the type species of the genus Enterobacter, and because it was only 41% related by DNA hybridization to Citrobacter freundii, the type species of Citrobacter. E. sakazakii had biochemical reactions very similar to those of E. cloacae but was d-sorbitol negative and positive for extracellular deoxyribonuclease at 2 to 7 days and produced yellow-pigmented colonies. E. sakazakii had larger zones of inhibition around ampicillin and cephalothin antibiotic disks, which also helps to differentiate it from E. cloacae. E. sakazakii grew on the nonselective (but differential) plating media commonly used in enteric bacteriology, but its plating efficiency was reduced on more inhibitory enteric plating media. It has been isolated from human clinical specimens such as sputum, feces, and wounds, where it is probably only a colonizer and not clinically significant. However, it is also a documented, although rare, cause of neonatal meningitis. Other sources have included food, a physician’s stethoscope, and an uninoculated blood culture bottle.
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