Resistance (R) factor-mediated streptomycin (Sm) resistance differs from classical, high-level, chromosome-borne Sm resistance in its dominance over sensitivity and in the level of its effectiveness (in Escherichia coli approximately 25 mug/ml versus >2,000 mug/ml). In addition, an R factor-containing strain, unlike high-level Sm-resistant bacteria, showed an inoculum effect with respect to its...