Physiological Streptomycin Resistance in a Multiauxotroph of Escherichia coli Strain 15 T

Escherichia coli strain WWU was found to be moderately resistant to streptomycin when grown in a minimal medium, although the strain was sensitive if grown in nutrient broth. Transfer experiments showed that cells grown in minimal medium retain the resistant state for a period of time after dilution into nutrient broth; and conversely, sensitive cells grown in nutrient broth were sensitive after dilution into minimal medium for a period of time. The kinetics of transition from resistant to sensitive and from sensitive to resistant were observed, and kinetics of (3)H-dihydrostreptomycin accumulation by resistant and sensitive cells were compared. The data suggested that cells grown in minimal medium were physiologically resistant because they accumulated streptomycin poorly. Inactivation per incorporated antibiotic molecule was the same in resistant and sensitive cells.