Differential activity of bacteriocins and cefotaxime against Serratia marcescens clinical isolate SMG40 and its pigmented variant.

Strain Serratia marcescens SMG40 was nonpigmented but yielded pigmented variants at low frequency. Of 15 tested bacteriocins, 10 were active against the original strain, but only 7 were active against the pigmented variant Pdg+. Moreover, active cephalosporins, e.g., cefotaxime, were more active against the Pdg+ variant than against strain SMG40. These reciprocal differences in susceptibility to some bacteriocins and to cefotaxime were maintained in subclones derived from Pdg+/- sectored colonies. However, mutants of pigmentation isolated from the Pdg+ variant were not modified with regard to bacteriocins and cefotaxime. Other clinical isolates of Serratia were examined for comparison, but strain SMG40 appeared to be unique.