Studies on the Microbiological Assay of Tylosin in Food

Abstract

Factors affecting the sensitivity and recovery of tylosin assay for various foods have been studies by the agar diffusion plate method with Sarcina lutea (ATCC 9341) as the test organism. And a modified cylinder-plate or paper disk-plate method was developed based on the experimental results, and brief outline of the technique is as follows:Extraction of tylosin from a food sample is carried out by addition of 4-fold volume of M/15 phosphate buffer of pH 8.0 to the minced sample, and it is homogenized by a blender. The supernatant or filtrate of the homogenate can be used as a test solution for tylosin assay (if necessary, further dilution should be made with the aforementioned extractant).Fifteen peni-cylinders or paper disks are placed in a 15cm diameter plate with a single 17ml seeded layer of modified streptomycin assay agar of pH 8.5. One test solution should be placed in each 3 cylinders or disks on 3 plates. Inhibition zone may be measured after being incubated for 16 to 18 hours at 32°C, and with the average diameter of 9 inhibition zone for one test solution, the tylosin concentration can be calculated in comparison with the standard curve prepared with standard tylosin solution series. Employing this method, the standard curve extends from 0.16 to 2.5ppm (μg/ml) which corresponds to the tylosin contents of about 1 to 16μg/g of sample.The sensitivity of the paper disk-plate method is about 1/4 that of the cylinder-plate technique under the identical condition.