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Group B Strep Prevention

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Laboratory Personnel, Slide 7

Hippurate Test
(Test for Free Benzenze)

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Hippurate Test
This test is an additional presumptive test used to aid in the identification of GBS. This test, the test for free benzene, is one variation of the hippurate hydrolysis test. Hippurate (hippuric acid) is a benzene (6 carbon) ring with the amino acid serine attached to one of the carbon molecules. Hippuricase, the enzyme, cleaves the benzene ring and the serine free from each other. The streptococcal cultures are inoculated into tubes containing hippuric acid and incubated overnight (the two larger tubes on the left). The next day the tube with growth is centifuged to sediment the bacteria. A small portion of the broth is pipetted into small tubes (two small tubes on the right). A reagent called ferric chloride is added to both tubes. If a strong precipitate forms and remains after 10 minutes, the test is positive for hippurate hemolysis. In the picture on this page, reading from left to right, the third tube (first small tube) is positive because it has remained cloudy. The forth tube (second small tube) is still clear, therefore it is negative.
Page Last Modified: April 20, 2008
Content Last Reviewed: April 20, 2008
Content Source: National Center for Immunization and Respiratory Diseases
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