Identification of acinetobacters on blood agar in presence of D-glucose by unique browning effect

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.

FIG. 1

Browning effect of glucose-oxidizing acinetobacters on blood agar containing glucose. A. baumannii ATCC 19606 (1) and a clinical isolate of A. baumannii (4) caused a light-brown discoloration (indicated by arrows) on glucose-containing Columbia Agar Base with blood of horse (HoB+), sheep (ShB+), or human (HmB+) origin but not on plain agar with blood of horse (HoB), sheep (ShB), or human origin. The browning effect was not observed when other nonfermenters such as P. aeruginosa (2), Stenotrophomonas maltophilia (3), non-glucose-oxidizing A. lwoffii (5), Flavobacterium meningosepticum (6), and Moraxella osloensis (7) were cultured on glucose-containing blood agar. In addition, the discoloration was not seen on glucose-containing chocolate agar (Cho+) or Columbia Agar Base (CAB+) or on plain chocolate agar (Cho) and Columbia Agar Base.

FIG. 2

Representative PCR profiles of the two most common Acinetobacter genospecies, A. baumannii (lanes 4 to 9) and A. lwoffii (lanes 1 to 3), with unique bands of 940 and 1,300 bp, respectively. Lane M, HaeIII-digested φX174 DNA molecular size markers.