Epidemiology and Genetic Analysis of Streptomycin-Resistant<i>Erwinia amylovora</i>from Michigan and Evaluation of Oxytetracycline for Control

Abstract

Streptomycin-resistant strains of Erwinia amylovora were isolated from 14 of 63 Michigan apple orchards surveyed during 1991-1993. Orchards with resistant strains were located in three geographically distinct areas. The genes encoding streptomycin resistance, strA and strB, were usually located on DNA homologous to transposon Tn5393 and to the self-transmissible plasmid pEa34. Ten percent of the resistant strains from one orchard contained DNA homologous to Tn5393 on the chromosome or a resident plasmid, pEA29. Plasmids homologous to pEa34 but lacking Tn5393 were rare in streptomycin-sensitive isolates, appearing in only three adjacent orchards 127 km from the nearest orchard with resistant strains containing pEa34 [...]