Inhibition of Dihydrostreptomycin Action on Mycobacterium smegmatis by Monovalent and Divalent Cation Salts

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Abstract
We have examined and compared the effects of monovalent and divalent cation salts on dihydrostreptomycin (DSM) action against Mycobacterium smegmatis . The Sauton synthetic liquid medium used was supplemented with test salts on the basis of ionic strength (μ). Turbidimetric growth experiments showed that 0.02 M MgSO 4 (μ = 0.08) prevented growth inhibition by 0.1 μg of dihydrostreptomycin per ml, but 0.02 M NaCl (μ = 0.02) did not. However, at molarities equivalent to μ = 0.08, four monovalent cation salts, including NaCl, Na 2 SO 4 , NH 4 Cl, and (NH 4 ) 2 SO 4 , all prevented inhibition by dihydrostreptomycin. When magnesium and sodium salts were compared at μ = 0.02, 0.04, and 0.05, two distinct growth protective patterns were seen. These data were indicative of two different mechanisms of dihydrostreptomycin antagnosim by salts; the first being divalent cation and concentration dependent, and the second being nonspecific and ionic strength dependent. Viability studies supported the existence of two mechanisms.