Detection of specific bacterial enzymes by high contrast metal chelate formation. Part I. 8-Hydroxyquinoline-beta-D-glucoside, an alternative to aesculin in the differentiation of members of the family Enterobacteriaceae.

8-Hydroxyquinoline-beta-D-glucoside has been shown to be a useful alternative substrate for the differentiation of members of the family Enterobacteriaceae based on the presence or absence of beta-glucosidase. In an identification protocol based on multipoint-inoculated plates 8-hydroxyquinoline-beta-D-glucoside when incorporated into an agar based medium supplemented with a ferric salt produced intense black pigmentation localised solely in the immediate vicinity of beta-glucosidase positive organisms. In contrast, using conventional aesculin plates, positive organisms produced a brown ferric-aesculetin complex, the diffusibility of which limited interpretation especially where large numbers of colonies were involved. Almost complete agreement was found when 1964 routine 'coliform' organisms were tested by both methods. The method described allows use of a 36 place 'minipin' inoculator without any danger of 'nearest neighbour' interference and constitutes a cost-effective method suitable for either manual or automatic reading.