Evaluation of four ONPG tests for Enterobacteriaceae from human, animal and selected food sources

An ortho-nitrophenyl-β-D-galactopyranoside (ONPG) test was done on 250 Enterobacteriaceae from human, poultry, and selected food sources by use of four commercially available miniaturized systems and by the conventional test for ONPG. For the 102 cultures from human and poultry sources, all four systems agreed with the conventional test as follows: API (98%), Difco (94.1%) Minitek (98%), and Pathotec (98%). For the 148 food isolates, the percent agreement between the conventional and these four systems was significantly lower, API (87.2%), Difco (85.8%), Minitek (88.5%), and Pathotec (85.8%).