describes how to set up and read test for toxigenicity of C diphtheriae

1. ELEK test Procedure and Interpretation

2. Filter paper preparation Cut filter paper 75% of the diameter of the agar plate Approx 2cm wide Saturate with Corynebacteriumdiphtheriaeantitoxin Allow to dry S Prithepaul 2011 2

3. The Medium Molten agar (plate count agar, nutrient agar, trypticase agar, Mueller Hinton agar) Add rabbit serum and potassium tellurite to molten agar Rabbit serum to enrich the medium and support growth of organism Potassium tellurite to restrict growth of possible contaminants and other organisms S Prithepaul 2011 3

4. The Medium contd.. Pour plates to depth of 5mm, aseptically Place prepared filter paper across the middle of the plate Allow the filter paper to settle to the bottom of the plate Allow plate to dry Allow surface moisture on plate to dry S Prithepaul 2011 4

5. Inoculation Use a pure culture of the test organism Streak the test organism at right angles to the filter paper strip Streak positive and negative controls parallel to the test organism Ensure that the positive control is next to the test organism S Prithepaul 2011 5

6. Incubation Incubate the plate for 18-24 hours, aerobically ate 37 degrees Celsius S Prithepaul 2011 6

7. Reading of plate Antitoxin (from the filter paper strip) and toxin (from the organism) diffuses out into the medium Where they meet, they form a white line of precipitation, at an angle of 45 degrees from the line of inoculation S Prithepaul 2011 7

8. Reading of plate contd.. The lines of precipitation of the positive control and a positive test give a wave like formation S Prithepaul 2011 8