Development of a latex agglutination test for rapid identification of Escherichia coli

Escherichia coli, one of the most important human pathogens, is usually identified by a battery of biochemical tests that require overnight incubation. For rapid identification of Escherichia coli, a latex agglutination test (LAT) was developed. Rabbits were immunized with cell-surface antigens extracted from Escherichia coli CCRC 15481 with 4 M urea, and the affinity-purified antibodies were used to coat latex particles for the identification of the bacterium. The following gram-negative bacteria were used to evaluate the LAT: Escherichia coli (n=761), Enterobacteriaceae other than Escherichia coli (n=632), Aeromonas spp. (n=21), Pseudomonas spp. (n=75), Vibrio spp. (n=18), and other bacteria (n=64). The LAT had a sensitivity and specificity of 99.2 and 93.3%, respectively. If the LAT was used in conjunction with the tests of indole production or lactose fermentation, the specificity values for the identification of Escherichia coli increased from 93.3 to 98.8 and 98.7%, respectively. If the LAT, indole production, and lactose fermentation were used together for the identification of Escherichia coli, the sensitivity and specificity were 94 and 99.7%, respectively. Lactose fermentation could be detected by observing the colonies grown on selective media (e.g. MacConkey agar), and indole production could be analyzed simply by the spot indole test. Strains producing negative reactions (i.e. not identified as Escherichia coli) should be processed by the conventional procedures for identification. The present protocol integrating the LAT, indole production, and lactose fermentation for the identification of Escherichia coli offers considerable savings of time, manpower, and cost.