Antibiotic Susceptibility of Erwinia amylovora Isolates from Fire Blight Diseased Pomaceous Fruit Trees in Georgia

Fire blight, caused by the bacterial pathogen, Erwinia amylovora is a devastating disease of fruit trees belonging to the Rosaceae family. The most susceptible species are apple, pear and quince. The economic loss caused by bacterial blight of fruit trees is manifested both in crop loss and rapid destruction of entire orchards. The bacterium enters the plant from stomata or wounds caused by insects and environmental influences - rain, wind, etc. It is difficult to control fire blight as the E. amylovora has significant survival capacity. For the development of effective control measures of fire blight, together with destruction of the diseased trees it is important to find effective antimicrobial preparations. The goal is to study the antibiotic susceptibility of the E. amylovora Georgian isolates. Dozens of the pathogen isolates were obtained and identified from the fire blight diseased apple, pear and quince trees in eastern Georgia. Their cultural and morphological properties, as well as the genetic diversity were studied. Susceptibility of these isolates towards eight antibiotics: streptomycin, penicillin, tobramycin, erythromycin, kanamycin, ofloxacin, trimethoprim and tetracycline by disc-diffusion method have been studied. The majority of E. amylovora isolates from different regions of eastern Georgia are sensitive to tobramycin, kanamycin, ofloxacin, tetracycline and streptomycin, with the exception of isolates ## 6052, 6053, 6162 and 8892, which express some resistance to streptomycin. The absolute majority of the Erwinia amylovora isolates are resistant to penicillin and trimethoprim, while the susceptibility to erythromycin is variable. Acknowledgements: This work is funded by the Shota Rustaveli National Science Foundation of Georgia (SRNSFG), grant number FR-19-22524. The participation of Dr. Fabio Rezzonico to this work was funded under project number IZ08Z0_177515 by the r4d Programme of the Swiss Agency for Development and Cooperation (SDC) and the Swiss National Science Foundation (SNSF). Key words: Fire blight, Erwinia amylovora, antibiotic susceptibility