Role of the outer membrane in the accumulation of quinolones by Serratia marcescens

Accumulation of four quinolones by Serratia marcescens was measured fluorom etrically. The passage of quinolones through the outer membrane was studied in both lipopolysaccharide-deficient and porin-deficient mutants. The lipo polysaccharide (LPS) layer formed a partially effective barrier for highly hydrophobic quinolones such as nalidixic acid. Quinolones with a low relati ve hydrophobicity coefficient seemed to pass preferentially through the wat er-filled Omp3 porin channels. Results were confirmed when Omp3 was cloned in a porin-defective Escherichia coli.