Fatin Naeem Abbas Oxidase test All members of

Fatin Naeem Abbas

Oxidase test: All members of enterobacteracae are oxidase – negative used to test pseudomonas species are oxidase positive. The reagent used to test the presence of oxidase is a paminodimethylaniline oxalate or tetra- methyl-pphenylenediamine hydrochloride.

Catalase test Some bacteria produce the enzyme catalase. All pathogenic organisms included in enterobacteracae (except shigella dysenterae) are catalase +ve. It can be tested by emulsifying a bacterial colony in a drop of H 2 O 2 on a slide. Catalase +ve organisms show effervescence

Indole test : This test demonstrate the ability of certain bacteria to decompose the amino acid tryptophane to indole which can be detected by the addition of Kovac's reagent after the incubation. The formation of a red ring on the surface of the medium is considered as a positive reaction.

Methyl red test: This test is employed to detect the sufficient amount of acid which is formed during fermentation of glucose. This result in decreasing the p. H of the medium to 4. 5. This can be detected by the addition of methyl red reagent to the medium after incubation. The development of a red is a positive reaction. n

Voges-Proskauer : This test detect the formation of a neutral product (acetyl methyl carbinol) during fermentation of glucose. This can be detected by the addition of Barritt's reagent after incubation. The development of a red color is considered a positive result.

Citrate utilization test : This test demonstrate the ability of bacteria to utilize the citrate as the only source of carbon. The medium used is Simmon, s citrate agar which contain the citrate as the only carbon source, . In addition to the p. Hindicator bromothymol blue. If the bacteria utilize the citrate it will liberate CO 2 which combine with sodium and result in sodium carbonate which is an alkaline product that change the color of the indicator from green to blue which is considered a positive reaction.

Urease test : This test demonstrates the ability of bacteria to produce the enzyme urease that degrade the urea into ammonia and H 2 O. The medium used contains urea and an p. H-indicator (phenol red). Thus when ammonia is formed the medium becomes alkaline so the color of the medium will be changed to deep pink, which is considered positive.

Motility test: This test detect the ability of bacteria to move. The medium used is nutrient broth that contains 0. 3 % agar. It is inoculated by tabbing to the bottom of the tube. If the bacteria is motile the growth will diffuse from the inoculation to the surrounding medium. But if the bacteria is non-motile the growth will be restricted to the inoculation.

TSI test : The medium used is called TSI agar that contains three kinds of sugars (glucose 0. 1 % , lactose 1%, sucrose 1%). In addition to ferrous sulfate and p. H-indicator (phenol red). This test demonstrate the following: 1. Alkaline slant (red) / Acid butt (yellow) ( K /A ): This reaction is of non- lactose fermenting bacteria which ferment only the glucose that is present in little amount in this medium (0. 1 %). Thus the amount of acid formed is little that just the butt will convert into yellow color. While the peptones present in the medium will be oxidized in the slant forming an alkaline products which convert the medium into a red color. 2. Acid slant (yellow)/ Acid butt (yellow) ( A / A ): This reaction is for lactose fermenting bacteria, which ferment the lactose that present in large amounts in the medium(1 %). Thus the acid that is formed is suffient that all the medium will be converted to yellow. 3. Alkaline slant (red) / Alkaline or no change in color butt (K/K or no change): This reaction is non fermentive (oxidative) bacteria, that cannot ferment any kind of sugar present in the medium. 4. Blackening in the butt: This due to the production of H 2 S that precipitate as ferrous sulfide. 5. Bubbles or break in the medium : due to the formation of gas.

Phenylalanine Can be converted by oxidative deamination to phenylpurivic acid (PPA) which can be identified by adding ferric chloride. proteus species are PPA positive.

Hydrogen –sulphate production (H 2 S) n To test the ability of the organism to produce H 2 S through breakdown of the salphur containing compounds in the medium n