## 1 Introduction  
_Erwinia amylovora_ is the type species of the genus _Erwinia_ that belongs to the family _Enterobacteriaceae_. As is common in bacterial taxonomy in recent years, there have been a continuous description of novel _Erwinia_ species as well as some species have been reclassified and transferred to other genera ([[http://www.bacterio.net](http://www.bacterio.net)]([http://www.bacterio.net](http://www.bacterio.net))). Most members of this genus cause diseases in plants and, historically, it is important to remember that _E. amylovora_ was the first bacterium demonstrated to cause disease in plant, a discovery made in the late 1800s, at the same period as a similar discovery with human and animal diseases [1; 2].  
_E. amylovora_ causes fire blight, a devastating plant disease affecting a wide range of host species within the _Rosaceae_ subfamily Spiraeoideae, and is a major global threat to commercial apple and pear production. Moreover strains infecting plants in the genus _Rubus_ belonging to the subfamily Rosoideae, including blackberry and raspberry, have also been reported [3; 4; 5; 6; 7].  
In the last two centuries this pathogen has spread worldwide [6; 7; 8] and, in consequence, _E. amylovora_ has been cataloged as a quarantine organism in the European Union, where it is subject to phytosanitary legislation [8], and, recently, has been included in the top 10 plant pathogenic bacteria published in the journal _Molecular Plant Pathology_[9].  
Among the limited number of control options currently available, prophylactic application of antibiotics (e.g., streptomycin or oxytetracycline) during the bloom period appears most effective [10]. However, regulatory restriction, public health concerns, and pathogen resistance development severely limit the long-term prospects of antibiotic use [11; 12]. Biological control measures may offer promising alternatives to minimize or even substitute the use of antibiotics, and to mitigate occurrence of resistance [5; 13].  
In the pathogenesis of _E. amylovora_, pathogen cells enter plants through the nectarhodes of flowers and other natural openings, such as wounds, and are capable of rapid movement within plants and the establishment of systemic infections [14; 15; 16; 17]. In susceptible hosts, bacteria first move through the intercellular spaces of parenchyma and, in a later stage, in the xylem vessels, thus provoking extensive lesions, and sometimes complete dieback of the tree, under favorable climatic conditions. The diseased parts of the plant become brown or black, as if they had been swept by fire [17].  
Many virulence determinants of _E. amylovora_ have been characterized, including the Type III secretion system (T3 SS), the exopolysaccharideacharide (EPS) amylovoran, biofilm formation, and motility [15; 18]. To successfully establish an infection, _E. amylovora_ uses a complex regulatory network to sense the relevant environmental signals and coordinate the expression of early and late stage virulence factors involving two component signal transduction systems, bis-(3'-5')-cyclic di-GMP (c-di-GMP) and quorum sensing [15]. In the present review, we present the recent findings on virulence factors of _E. amylovora_ research, focusing on their role in bacterial pathogenesis and on the aspects that deserve future research.