Fire blight, caused by bacterium Erwinia amylovora, is described as one of the most important diseases of apples and pears in the world. It parasitizes more than 160 plant species belonging to around 30 different genera. In Europe, it was first observed in 1957 in the UK. In Croatia it was discovered in 1995 in Nuštar. In English, name of this disease ("Fire blight") resembles characteristic symptom by which the parts of the plant appear to have been burnt. The paper describes the characteristic symptoms of this disease as well as its life cycle and control. Control of this phytopathogenic bacterium is a major challenge in agricultural practice, especially in conditions favorable to the onset and spread of infection. A large problem in control of this disease is that there is no chemical plant protection compound that could successfully control the disease. Good effect has antibiotic streptomycin, but he has no permission of use in our country. In addition, in countries where it has been used for long time, resistance of the pathogen has appeared. The use of antibiotics, except its environmental context, also requires high costs, so the problem of economic justification is just one of the reasons for its ban. The aim of this graduate thesis was to conduct a diffusion test for the checking of streptomycin antibiotic activity on the phytopathogenic bacterium Erwinia amylovora by using various volumes of overnight bacterial culture. A hypothesis that the diffusion test, useing 50 ml of overnight bacteria control is suitable for testing the antibacterial activity of streptomycin on mentioned bacterium was confirmed.