Unveiling Antibiotic Resistance: Genome Sequencing of Streptomycin-Resistant Erwinia amylovora Isolate

Erwinia amylovora, the causal agent of fire blight, poses a serious threat to several rosaceous plants, especially apples and pears. In this study, a spontaneous streptomycin-resistant E. amylovora strain (EaSmR) was isolated under laboratory conditions. Compared with the parental strain TS3128, the EaSmR strain exhibited high resistance to streptomycin (>100,000 µg/mL) and showed a significant reduction in both swimming and swarming motility. To investigate the mechanisms underlying streptomycin resistance, the genome of EaSmR was sequenced, and four single nucleotide variants (SNVs) were identified in comparison with the EaSmR genome with TS3128. Two genes in EaSmR were found to contain SNVs relative to TS3128, including a point mutation at codon 43 in the rpsL gene, the primary target of streptomycin, which was identified as the cause of the resistance. Additionally, three other point mutations were detected within the gene encoding type I methionyl aminopeptidase (MetAP1), resulting in an amino acid substitution from serine to valine (S76V). Furthermore, we analyzed the nonsynonymous single nucleotide variants (nsSNVs) between the EaSmR isolate and the reference type strain, CFBP1430. A total of 111 nsSNVs were found in EaSmR, including three stop-gain mutations, across 102 genes, which likely account for potential differences between the Korean strain TS3128 (EaSmR) and the reference strain CFBP1430. Whole-genome sequencing of EaSmR reveals significant genetic changes and provides valuable insights into the role of single nucleotide variants in antibiotic resistance and altered physiological traits. As the first report of a laboratory-induced, streptomycin-resistant E. amylovora strain from South Korea, this study provides essential insights into resistance mechanisms and highlights key genomic differences that may contribute to the unique characteristics of the Korean strain, establishing a valuable foundation for future disease management strategies.