Measurement of inhibition zone diameter in disk susceptibility tests by computerized image analysis

This paper presents an application of computerized image analysis in microbiology. This application permits the automatic detection and diameter measurement of inhibition zones in disk susceptibility tests. Each inhibition zone boundary was extracted according to an edge detection method based on the Student's t-test and a priori knowledge (geometry, densitometry). Evaluation of the method was performed by comparing the results from an image analyser and a trained observer. For this purpose, we used kappa statistics and obtained a close agreement (a kappa coefficient equal to 0.84) on a set of about 600 inhibition zones. The results encourage us to develop the method further to include the detection of antagonism and synergism.