Extended longevity of <i>Erwinia amylovora</i> vectored by honeybees under in vitro conditions and its capacity for dissemination

Abstract

Abstract Fire blight outbreaks in Korea were first reported in 2015. Regular outbreaks have occurred since, indicating a continuous cycle of the fire blight pathogen in Korea. We determined the role of Apis mellifera (honeybee) as a vector of Erwinia amylovora by verifying the following: (a) E. amylovora longevity in/on honeybees; (b) the most common body parts that carry the bacteria; (c) the rate of bacterial spread to healthy host organs; and (d) the relationship between dispersal of viable but nonculturable (VBNC) and virulent bacterial cells. E. amylovora survived for 15 days on the exterior of honeybee bodies and was most abundant on the abdomen in comparison to other areas such as the labellum, wings, and hind legs. In the digestive system of honeybees, E. amylovora survived for 7 days, and bacteria were found in faeces for 3 days after exposure. The bacteria are likely to be VBNC on honeybees. Honeybees that were contaminated with bacteria transferred E. amylovora to healthy immature apple fruit, shoots, and flowers for 10 days after exposure. E. amylovora was also transferred from inoculated plant parts to uncontaminated honeybees. In addition, bacteria moved from inoculated plant tissues to unexposed honeybees and then from these honeybees to healthy plant tissues. Therefore, E. amylovora can survive in/on honeybees for extended amounts of time, which contradicts previous reports. The bacteria moved to host tissues via honeybees, suggesting that honeybees are the vectors of E. amylovora and play a role in the development of new outbreaks of fire blight disease in the central regions of Korea.

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