Small Colony Variants of Escherichia coli

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Abstract
Stable small colony variants of 4 strains of E. coli were produced in large numbers in synthetic medium containing low concs, of 2-methyl-l,4-naphthoquinone. Reversion to forms indistinguishable from parent strains was achieved and occurred more readily in medium enriched with glucose or tryptose or both. Original cultures, reverted cultures and s.c.v. were all methyl-red-positive and Voges-Proskauer-negative. Original and reverted strains all reduced NO3 to NO2 and all were indole-positive. S.c.v. from 2 of the 4 coli strains reduced NO3 and produced indole; those from the remaining 2 strains were indole- and nitrite-negative. Growth of original and reverted strains in plain or sucrose broth produced alkali; growth of s.c.v. in plain or sucrose broth failed to change the pH significantly. The theory is advanced that s.c.v. arise after inhibition or destruction of enzyme systems necessary for normal growth by agents with some degree of antibacterial activity. The possibility that they are present in small, undetectable numbers in original cultures and, being more resistant, are able to multiply and make themselves apparent in concs. of antibacterial inhibitory to normal cell growth has not been ruled out, but it is actually not important in elucidating their origin.