Lipopolysaccharide recovery restores susceptibility levels towards beta-lactams in Serratia marcescens.

O-side chain-defective spontaneous mutants of Serratia marcescens, selected by phage resistance, showed lower MICs against various beta-lactams than did their parental strains. The recovery of their ability to produce O-antigen restored the original MIC values, as well as phage susceptibility. The permeability coefficients of wild-type, O- mutants, and revertants, demonstrated that O-antigen modifies the permeability of antibiotics in S. marcescens.