ERWINIA AMYLOVORA SURVIVES IN NATURAL WATER

The role of water in the dissemination of Erwinia amylovora has not been demonstrated, although it has been recently shown that this pathogen can survive in sterile water and maintain its pathogenicity for up to three years (Biosca et al., 2006a, 2006b); however, its survival in non-sterile natural water has not yet been investigated. In this study, the survival of E. amylovora under natural oligotrophic conditions of rain water microcosms was monitored for 45 days at 26°C, using sterile water microcosms as control. Microscopic bacterial cell counts were monitored by the Live/Dead viability kit and culturability by plate counts on non-selective King's B medium. The pathogenicity of E. amylovora cells from these microcosms was evaluated by inoculating immature pear fruits. The pathogen was able to survive in rain water microcosms in the presence of water microbiota at warm temperatures during the experimental period. However, a progressive loss of culturability of E. amylovora on solid media, from 10⁷ to 10⁵-10³ cfu/ml, was observed with time. This loss was more pronounced in nonsterile water. This was concurrent with an increase in the numbers of native bacteria present in some rain water samples, suggesting that the survival of this pathogen was affected by nutrient limitation as well as by bacterial competition. Starved cells of E. amylovora in natural water retained their pathogenicity on pear fruits. These results demonstrate, for the first time, the survival of E. amylovora in natural water and the risk of environmental waters as reservoirs and dissemination ways for this bacterium.