The feasibility of using a specific phage (AR1) in conjunction with a conductance method for the identification of Escherichia coli O157:H7 was evaluated. The multiplication of strains of E. coli
O157:H7 was inhibited by AR1; therefore, a time point (detection time, DT) at which an accelerating change in conductance in the culture broth was not obtained. Bacterial strains were subcultured on sorbitol-MacConkey
agar and incubated at 35°C for 24 h, and the ability of the bacteria to ferment sorbitol was recorded. An aliquot of 0.5 ml of the bacterial suspension (107 CFU/ml) and 0.5 ml of the phage
suspension (108 PFU/ml) were added to the conductance tube of a Malthus analyzer containing 5 ml of culture broth. The tubes were incubated at 35°C, and conductance changes in the tubes were
continuously monitored at 6-min intervals for 24 h by the instrument. A positive reaction was defined as an E. coli strain that could not utilize sorbitol and caused no conductance change (i.e.,
no DT) within an incubation period of 24 h. Of the 41 strains of E. coli O157:H7 tested, all produced positive reactions. When a total of 155 strains of non-O157:H7 E. coli were tested, 14
did not have a DT within 24 h. However,among these 14 strains, 13 were sorbitol fermenters, and the remaining one was a nonfermenter. Therefore, by definition, only one strain produced a false-positive
reaction. The sensitivity and specificity of the present method were 100% (41 of 41) and 99.4% (154 of 155), respectively. The present method incorporating conductimetric measurement and phage AR1 for the
identification of E. coli O157:H7 was simple and capable of automation.
Document Type: Research Article
Department of Medical Technology, College of Medicine, National Cheng Kung University, 1 University Road, Tainan 701, Taiwan, Republic of China 2:
Food Industry Research and Development Institute, 331 Food Road, Hsinchu 300, Taiwan, Republic of China
Publication date: January 1, 2002
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