Fire blight is a devastating disease affecting rosaceous plants such as apple, pear and quince (Vanneste, 2000). The Gramnegative bacterium Erwinia amylovora is the aetiological agent of the disease. Currently, the main methods to control fire blight are the use of biological and chemical pesticides, antibiotics and resistant cultivars obtained through classical breeding or genetic engineering. Infected cultivars commonly require quarantine, pruning and/or eradication of the plants (Gusberti et al., 2015). Within the E. amylovora genome, the ams operon is necessary for pathogenicity and is responsible for the synthesis of amylovoran (Bugert & Geider, 1995), which is a complex branched heteropolysaccharide that is essential for virulence and pathogenicity, and is the major component of the exopolysaccharide (EPS) capsule of the bacterium together with levan (Caputi, Cianci et al., 2013; Caputi, Nepogodiev et al., 2013; Geier & Geider, 1993; Nimtz et al., 1996; Bernhard et al., 1993; Wuerges et al., 2015). The AmsI protein, encoded by the amsI gene, is a cytoplasmatic key enzyme of amylovoran metabolism, and thus a potential drug target for the control of fire blight.