ISHS Acta Horticulturae 273: V International Workshop on Fireblight
ISOLATION OF LYTIC PHAGES OF E. AMYLOVORA. |
| Authors: | J.L. Vanneste, J.P. Paulin |
| Abstract:
Sensitivity of bacteria to bacteriophages has been used to help identify bacterial pathogens of-humans, animals and plants. Several authors described isolation of phages that lyse E. amylovora (Baldwin et al,1963; Billing et al, 1960; Hendry et al, 1967; Erskine, 1973); bacteriophages of E. amylovora that lyse specifically capsulated cells or non-capsulated cells have also been described (Billing, 1960). In this study, we report the isolation of lytic bacteriophages that have been used in the laboratory, along with other determinative tests, to confirm the identification of E. amylovora. Bacteriophages were isolated from different sources as listed in Table 1. The samples were enriched with E. amylovora strain 1430 before being assayed for the presence of bacteriophages. When plated onto an overlay seeded with 1430, the plaque morphology varied from pin-point plaques to large clear plaques surrounded by a halo which enlarged with incubation time. Phages that lyse E. amylovora and produce plaques surrounded by such halos have previously been reported (Ritchie and Klos, 1977). These halos were shown to be caused by a soluble capsular polysaccharide depolymerase produced by the phages (Hartung et al, 1988; Vandenbergh and Cole, 1986). To determine the host range of the lytic phages isolated, we tested their ability to produce plaques on i) strains representative of the genera of the plant pathogenic bacteria, ii) epiphytic bacteria isolated from fire blight host plants iii) strains isolated with E. amylovora from fire blight lesions. Of the plant-pathogenic strains tested, only those belonging to the genus Erwinia were sensitive to the phages (Table 2). Moreover, none of the phages produced plaques on any of the 68 epiphytic strains isolated from Pyrus, Malus or Crataegus (Table 2) nor on any of the 22 non-E. amylovora strains isolated from fire blight lesions. Of the Erwinia species strains tested (Table 3) one strain of E. rhapontici, one strain of E. stewartii, and 8 strains of E. herbicola were sensitive to at least one phage, though none of these strains were sensitive to all the phages. In contrast, 165 strains of E. amylovora out of the 175 strains tested (94 %) were sensitive to all the phages. The 10 other strains were sensitive to at least 1 phage. In conclusion, ten lytic phages were isolated, none seem to be completely specific of E. amylovora, however only E. amylovora strains were sensitive to all the phages. Sensitivity to these bacteriophages has been used in the laboratory for routine tests as an additional tool to confirm identity of E. amylovora. | |
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