Abstract
Campylobacter jejuni usually hydrolyzes hippuric acid to benzoic acid and glycine, and a simple hippurate hydrolysis test is used to rapidly distinguish C. jejuni from C. coli in many clinical microbiological laboratories. However, sometimes the test gives variable results, which might be due to the inadequate number of bacterial cells in the test sample. In this study, we investigated the optimum number of bacterial cells required to perform the test smoothly. A total of 100 Campylobacter strains were included in this study, and test bacterial cell suspensions were prepared matching the McFarland units 0.5, 1, 2, 3, 4, and 5. Ninhydrin was added to the cell suspension and the color change was measured at an optical density of 540 nm. The test of bacterial suspensions of C. jejuni matching the McFarland units 1, 2, 3, 4, and 5 showed positive results for all suspensions. On the other hand, bacterial cell suspension of C. coli matching a McFarland unit of more than 5 gave false positive results. Reproducible results were obtained with a bacterial suspension that matched the McFarland unit 2 and this number of bacterial cells may be used for the hippurate hydrolysis test to distinguish C. jejuni from C. coli.
