Preliminary physiologic characterization and genetic analysis of a new Escherichia coli mutant, lov, resistant to mecillinam.

A mutant of Escherichia coli resistant to mecillinam was selected. The target of this antibiotic is penicillin-binding protein 2 (PBP2), which is active in cell wall elongation and responsible for the rod-like shape of the organism. Several observations indicate that PBP2 remains active in the mutant. For example, cells are small and rod-shaped in the absence of mecillinam but become spherical in its presence; the formation of filaments in the presence of furazlocillin shows that cell wall elongation still takes place. The mutant also has a low growth rate and small cell volume, even in rich medium. In these respects, the mutant resembles cya or crp strains (in which the cyclic adenosine monophosphate-catabolite activator protein [cAMP-CAP] complex is inactive), although its catabolic capacities are unaffected. The mutation, called lov, lies at 41 minutes on the E. coli genetic map. The phenotype is partially suppressed by the P1-mediated transduction of an rpsL ribosomal mutation conferring streptomycin resistance.