The Hippurate hydrolysis test differentiates β-hemolytic Streptococcus agalactiae from other β-hemolytic streptococci.Glycine is detected by using the Ninhydrin reagent which forms a deep purple or violet color.The Hippurate hydrolysis test detects the organism’s ability to produce hippuricase enzyme that hydrolyzes hippurate substrate into glycine and benzoic acid.Ferric citrate is present in the medium and when it reacts with esculetin, it turns the entire medium dark brown to black due to the formation of the phenolic iron complex.Įnterococcus faecalis Hippurate hydrolysis test.The bile esculin test determines the ability of organisms to hydrolyze esculin when in the presence of bile, esculetin is formed.Esculin is the differential ingredient that differentiates Enterococcus from Streptococcus.Bile esculin agar medium is both selective as well as the differential medium in which its selective ingredient is bile that inhibits the growth of other gram-positive bacteria except enterococci and some streptococci species.Bacitracin resistant non-Group A streptococci:.
Some of the specific biochemical tests for the identification of gram positive bacterial species are: The cell wall composition of gram-negative and gram-positive bacteria differs that is why the mechanism of Gram staining in the decolourizing step acts differently in both of the bacteria resulting in two different colors for identification. Gram-positive bacteria retain purple color from the primary dye while gram positive bacteria retain the counterstain color and appear pink or red color when visualized under a microscope. Gram staining is a differential staining technique that differentiates bacteria on its ability to retain color. Gram staining for identification of gram positive bacteria Shape, size (in mm), color, consistency, opacity, elevation, and margin are determined and noted down for further identification. The colony morphological characteristics are observed from the culture plate. Morphological observation of culture colonies is also observed before these tests.ĭiscover gram positive bacteria with accuracy using biochemical tests for identification.Gram staining is the first step for the identification of an unknown bacterial culture followed by specific biochemical tests as described in Bergey’s manual.Due to its low lipid and lipoprotein content in its cell wall, gram-positive bacteria are highly susceptible to antibiotics but are resistant to physical disruption because of its multilayered peptidoglycan.Then, the 95% ethyl alcohol acts as a decolorizer that dehydrates and shrinks the peptidoglycan layer making the formed complexes unable to escape that result in purple stained cells.Crystal violet is a water-soluble dye that enters the peptidoglycan layer and forms crystal violet-iodine complexes.Gram-positive bacteria retain the crystal violet dye by its thick layer of peptidoglycan and appear purple color when observed under the microscope after performing Gram staining.
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