Identification of Acinetobacters on Blood Agar in Presence of d -Glucose by Unique Browning Effect

Abstract

ABSTRACT A positive phenotypic characteristic of glucose-oxidizing acinetobacters was demonstrated with blood agar containing d -glucose. Glucose-oxidizing Acinetobacter baumannii , Acinetobacter genospecies 3, Acinetobacter lwoffii , and Acinetobacter genospecies 13 sensu Tjernberg and Ursing caused a unique brown discoloration of media supplemented with 5% blood (of horse, sheep, or human origin) and an aldose sugar (0.22 M d -glucose, d -galactose, d -mannose, d -xylose, or lactose). The browning effect was not observed when a ketose sugar ( d -fructose or sucrose) was substituted for the aldose sugar or under high osmolarity in the presence of mannitol, glycerol, or sodium chloride. Other gram-negative nonfermenters (non-glucose-oxidizing acinetobacters, Pseudomonas aeruginosa , other Pseudomonas spp., Stenotrophomonas maltophilia , Flavobacterium spp., and Moraxella spp.) did not cause similar discoloration. This novel browning effect may serve as an alternative trait for identifying glucose-oxidizing acinetobacters.