Some properties of Serratia marcescens, Salmonella paratyphi A, and Enterobacter cloacae with non-enzyme-dependent multiple resistance to beta-lactam antibiotics, aminoglycosides, and quinolones.

Non-enzyme-dependent multiple-drug resistance occurs preferentially in some genera of Enterobacteriaceae, such as Serratia, Klebsiella, Enterobacter, and Salmonella. Susceptibility to beta-lactam antibiotics, aminoglycosides, quinolones, trimethoprim, and chloramphenicol may be affected in various combinations in different mutants. Proteins from the outer and inner membranes and lipopolysaccharides may be altered concomitantly. Although porin alterations have been observed in all resistant mutants studied, these modifications alone do not seem sufficient to explain the various cross-resistance phenotypes.