Question

What is the purpose of Mineral Oil in the API-20E test?

What could happen if a purity plate is not set up from the bacterial suspension in the API test?

What happens if the oxidase test is positive for an organism being identified using an API-20E strip?

Why does bacterial growth decrease as the solute concentration increases? Explain this phenomenon.

Answer 1

1) API 20 E test used for presence of various type of bacteria in sample. This is a quiche and simple test which detect 20 type of bacteria at a time . Some of test detect presence of anaerobic bacteria. So in those wells mineral oil is added to make environment anaerobic as these bacteria fo not survive in presence of oxygen.

2) purity plate is set along with each test, to determine the presence of single bacteria in culture. Single bacterial suspension is added to the test well , same added to agar plate. If agar plate gives mix culture than should repeat the test. If we not put purity plate than the results after test will not give guarantee to accurate ( means whatever test we are getting is due to single bacteria or may be mixture of bacteria)

3) API 20 test is done to detect only oxidase negative bacteria. So we will be not able to detect oxidase positive bacteria using this test.

4) as solute concentration increases in the medium it makes medium hypertonic. So it will lead to removal of water from bacteria in the medium and lead to decreased bacteria growth. This process is known as exo osmosis.