Antimicrobial susceptibility of Salmonella typhimurium carrying the outer membrane permeability mutation SS-B

Abstract

The antibiotic susceptibility profile of Salmonella typhimurium SS-B, a mutant susceptible to some antimicrobial agents, was studied in detail. Twenty-eight agents were tested, and eleven of these had MICs significantly lower (32- to greater than 250-fold) for the SS-B strain than for its parent. The drugs were generally hydrophobic or amphiphilic. Polymyxin B nonapeptide, which has a known outer membrane permeabilizing action, further reduced the MIC of several of these agents for the SS-B strain by a factor of approximately 10 to 30. In most cases, the resulting MICs were lower than the corresponding MICs for the parent strain grown in the presence of polymyxin B nonapeptide. In addition, the hydrophobic fluorescent probe N-phenyl naphthylamine was rapidly embedded in the membranes of the SS-B strain but was poorly embedded in those of the parent strain.

Inhibitory Spectra and Modes of Antimicrobial Action of Gallotannins from Mango Kernels (Mangifera indicaL.)

“…In analogy to previous studies probing the role of the outer membrane in resistance to antimicrobial agents, LPS mutants of S. enterica (18,47) were found to be more susceptible toward hepta-O-galloylglucose than was the wild-type strain. In addition to its properties as a physical barrier, the negatively charged outer membrane might limit binding of the negatively charged gallotannins through electrostatic repulsion.…”

The lipid A biosynthesis mutation lpxA2 of Escherichia coli results in drastic antibiotic supersusceptibility

“…Bacterial mutants which produce defective, heptose-deficient LPS consisting only of the lipid A-2-keto-3-deoxyoctulosonic acid (KDO) portion have lost part of the barrier function (15,18,28). However, there are other, less-characterized mutants which appear to be even more susceptible to hydrophobic and certain other antibiotics than the heptosedeficient mutants (10,31).…”

“…Salmonella typhimurium LT2 strain SH5014 (LPS chemotype Rb2) is a typical and well-characterized representative of rough S. typhimurium and was widely used in our previous susceptibility studies (27,29,31,34). SH7616 is its antibiotic-supersusceptible class SS-B mutant (29,31), and SH7622 is its antibiotic-supersusceptible ssc-1 mutant (10,29).…”

“…SH7616 is its antibiotic-supersusceptible class SS-B mutant (29,31), and SH7622 is its antibiotic-supersusceptible ssc-1 mutant (10,29). SL1102 (39) is an S. typhimurium strain with mutation rfaE543 (causing LPS chemotype Re).…”

“…The MICs of the antibiotics were measured in L broth (32) as described previously (31). The inoculum was L agar-grown cells, and the inoculum size was 104 cells per ml.…”