Question

Summarize the advantages of multi-test systems like Enterotube and API test strips

Answer 1

Multi test kits have the advantage of being ready to use, require minimal storage, stable at room temperature for long time. Multiple biochemical reactions for test organism can be performed simultaneously. These tests are economical and used for better and rapid identification.

The API (20E), and Enterotube are two test kits that are widely used for identification of Enterobactericeae. In the API 20E kit, the plastic strip consists of 20 microtubes (Cupules) that have dehydrated media of define composition for each biochemical test. The media in all tubes are inoculated with a suspension of the test organism in distilled water using Pasteur pipette. The cupules are incubated for 18-24 after overlay with mineral oil. Tests that can be performed are o-nitrophenyl-?-D-galactosidase, arginine dihydrolase, lysine/ornithine decarboxylase, citrate utilization, H?S production, urease, indole from tryptophan, tryptophan deaminase, Vogus proskauer for acetoin production, glucose, mannitol, inositol, sorbitol, rhamnose, sucrose, melibiose, amygdalin, arabinose, gelatinase. Motiliy and oxidase cannot be measured. The API kit is around 96-97.7% reproducible. However with citrate utilizations, to reproducibility decreases to 89%. The API strips require saline for suspension of colony for rehydration. Hence, preparation time is longer than Enterotube. An analytical profile index is used in interpretation of results. Easy addition of reagent is possible. A seven digital code is use for identification of the organism.

The Enterotube consists of a plastic tube that have 12 compartments of media in agar slopes. The media are inoculated with a single colony suspension. Inoculation is performed by withdrawing a pre-sterilised inoculating wire through the media. Although, generally 24-hour incubation is sufficient, some slow lactose fermenting strains require longer incubation time. This system combines nine tests that are used for biochemical identification of Enterobactericeae. All tests are performed with single inoculum. These include dextrose, ornithine, adonitol, Vogus Proskauer, arabinose, sorbitol,hydrogen sulphite/indole, urea, dulcitol, lactose, lysine and citrate. This kit is 95% efficient. The Enterotube system is faster to use as a single colony be directly picked up with the tube for inoculation. Some of the compartments can be used in anaerobic conditions while other can be used in aerobic conditions. The Enterotube system is around 97% efficient but can give false positive results.