Table 7. Mechanisms of streptomycin resistance in Erwinia amylovora
Genetic mechanism
Effect
MIC (ppm)1
Occurrence inErwinia amylovora
Mutation in the bacterial gene rpsL, which encodes a subunit of a bacterial ribosome
Streptomycin cannot bind to mutant ribosome
> 2,000
Chromosomal mutation; prevalent in the western US, Israel, and New Zealand; also found in Michigan
strA-strB
Encodes an enzyme (phosphotransferase) that inactivates streptomycin
500-750
Usually associated with transposon Tn5393 on plasmids; prevalent in Michigan; also found in California
1Minimal inhibitory concentration (in parts per million): the lowest concentration of antibiotic that completely inhibits bacterial growth.
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