Isolation of Streptomycin-Resistant Isolates of Erwinia amylovora in New York.

Streptomycin is currently the only antibiotic registered for the control of fire blight, a devastating disease of apple (Malus), pear (Pyrus), and other rosaceous plants caused by the bacterium Erwinia amylovora. Resistance of E. amylovora to streptomycin was first identified in California pear orchards in 1971 and is currently endemic in many parts of the United States. The Northeast remains the only major U.S. apple-growing region without streptomycin-resistant isolates of E. amylovora. In 2002, during a routine survey for streptomycin resistance, isolates from two neighboring orchards in Wayne County, NY were found to be highly resistant to streptomycin at a concentration of 100 μg/ml. This constitutes the first authenticated report of streptomycin resistance in New York State. Infected trees were shipped at the same time from a single nursery in Michigan. Resistance was caused by the acquisition of the strA-strB gene pair, inserted into the ubiquitous nontransmissible E. amylovora plasmid pEA29. Previously, streptomycin-resistant E. amylovora populations from Michigan were described with a similar mechanism of resistance, although the strA-strB genes are not unique to Michigan. These findings illustrate how unintentional movement of nursery material could undermine efforts to prevent the spread of antibiotic-resistant E. amylovora.