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Api 20E. principle. The API 20E System is a standardized, miniaturized microtube system consisting of 21 conventional “basic” and 6 supplementary biochemical tests used for the identification of Enterobacteriaceae and other non-fastidious Gram-negative bacteria.
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principle • The API 20E System is a standardized, miniaturized microtube system consisting of 21 conventional “basic” and 6 supplementary biochemical tests used for the identification of Enterobacteriaceae and other non-fastidious Gram-negative bacteria. • The API 20E System consists of microtubes containing dehydrated substrates. The substrates are reconstituted by adding a bacterial suspension. • They are then incubated so the organisms react with the contents of the tubes. Finally, they are then read when the various indicator systems are affected by the metabolites or added reagents, generally after 18 to 24 hours incubation at 35 - 37°C. Refer to API 20E package insert for the principles involved in each of the reactions, reactive ingredients and quantity of ingredients in each tube. Cupule tube
Biochemistry A)Basic tests • ONPG : ortho-nitrophenyl b-D-galactopyranoside. • ONPG is a substrate that have B-galactosidic bond “like lactose” but didn’t need permease to enter bacterial cell. • ONPG “colourless” galactose + ortho-nitrophenol “yellow/pale yellow” B-galactosidase + + + -
Biochemistry • ADH : arginineDihydrolase • argeninecitrullin + NH3 • citrullin + phosphate ion carbamoil phosphate + ornithine • carbamoil phosphate ATP + CO2 + NH3 • This microtube contains phenole red indicator • orange color consider +ve only in first 24h ADH Catabolic argininecarbomolytransferase Carbamoilkinase 6.8 8.4 + -
Biochemistry • LDC : lysine decarboxylase. “as LIA” Lysinecadaverine(pH ) +CO2 • ODC : ornithinedecarboxylase. “as MIO” ornithineputriscine(pH ) +CO2 LDC Phenole red + - ODC Phenole red + -
Biochemistry • CIT : testing the ability of bacteria to utilize citrate as a carbon source sodium citrate acetic acid + oxaloacetic acid Na +CO2+H2ONa2CO3CO2+pyruvate ammonium saltNH3+NH4OH bromothymol blue : yellow (6) > green (6.9) > blue (7.6) Citrate layase OAA decarboxylase + -
Biochemistry • H2S : H2S production test. sodium thiosulfate H2S (g) H2S ferrous sulfide “black ppt” • URE : urease utilization test. urea 2 CO2 + NH3 • urease works at both aerobic and anaerobic conditions, but it prefers the second. Reduction “H+” Ferrous sulfate + - urease Phenol red + -
Biochemistry • TDA : tryptophan deaminase. tryptophan indole-pyruvic acid “form within 24 h” + NH3 indole-pyruvic acid +10%FeCl3+ HCl + hydrazine ferric hydrazon HCl added to TDA reagent to break dow the product of the reaction between FeCl3 and tryptophan to prevent false positive rasults. TDA “” Reddish brown ppt ”” + -
Biochemistry • IND : tryptophan utilization test. tryptophan indole + pyruvic acid + NH3 indole pink or red “with or without ring” • VP : Voges Proskauer test. sodium pyruvate 2,3- Butanediol acetoin red color “within 10 min” arrangement of reagents application is not necessary because of the absence of peptone tryptophanase Kovac’s reagent Isoamyl alcohol + HCl + para-nitrophenylaminobenzaldehyde + - Barrit’s reagent + creatine VP “1” : 40% KOH VP ”2” : 5% alpha-naphthol + -
Biochemistry • GEL : gelatin liquefaction test. gelatin + cool chart black ppt 12-20 : sugar fermentation/oxidation tests. sugar fermentation or oxidation acid product +ve“yellow” 21. Oxidase test : performed on external fresh culture. gelatinase + - + Bromothymol blue -
note Fermentation (Enterobacteriaceae, Aeromonas, Vibrio) 1. Fermentation of the carbohydrates begins in the most anaerobic portion (bottom) of the tube. Therefore, these reactions should be read from the bottom of the tube to the top. 2. A yellow colour at the bottom of the tube only indicates a weak or delayed positive reaction. Oxidation (Other Gram-negatives) 1. Oxidative utilization of the carbohydrates begins in the most aerobic portion (top) of the tube. Therefore, these reactions should be read from the top to the bottom of the tube. 2. A Yellow color in the upper portion and a blue color in the bottom portion of the tube indicate oxidative utilization of the sugar. This reaction should be considered positive only for non-Enterobacteriaceae Gram-negative rods. This is a negative reaction for fermentative organisms such as Enterobacteriaceae.
BiochemistryB)Supplementary tests “needed only with multitaxon code” oxidation test tube fermentation test tube • 1% glucose • Nutrient agar • Bromothymol blue • 1% glucose • Nutrient agar • Bromothymol blue • Sterile mineral oil
BiochemistryB)Supplementary tests Note: if these tests used, you have to delay the reading of all result for 48h
material • API 20 E Strips • Incubation boxes “ tray and lids” • Report sheets • Sterile syringe and needle • Disposable plastic inoculating loop • 5 ml sterile normal saline • Sterile Mineral Oil • MacConkey agar plate
Interpretation • On the report sheet, the test are separated into groups of three and number 1 , 2 or 4 is allocated for each test. By adding the numbers corresponding to the positive reaction within each group, a7- digit profile number is obtained for 20 tests of the API 20E strip. • The 7- digit profile is then compared with the numerical profile in the API 20 E analytical profile index book to obtain the organism identification.
