TABLE 2.

Efficiency of colony formation on Mtz-containing medium^a

Strain	Mtzr frequency
26695 wild type (type I)	∼10−4
26695 rdxA	∼1.0
26695 frxA	∼10−4
26695 fdxA	<10−8
26695 fdxA rdxA	∼10−4
26695 fdxA frxA	∼10−4
26695 fdxA rdxA frxA	∼1.0
SS1 wild type (type II)	<10−8

^aEfficiency of colony formation on BHI agar containing 8 μg of Mtz per ml. When this efficiency is less than 1.0 (which implies that the strain is fully resistant to Mtz), this frequency generally corresponds to frequencies of new Mtz^r mutants, generated and selected by the mutagenic and bactericidal properties of Mtz once activated.