New Salmonella typhimurium mutants with altered outer membrane permeability

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Abstract
Three new classes of S. typhimurium mutants with increased sensitivity to hydrophobic agents are described. In contrast to many previously described mutants, the phage sensitivity pattern of these mutants did not give any indication of defective lipopolysaccharide. They had no detectable changes in their phospholipid or outer membrane protein composition, and their growth rate and cell morphology were normal. Class B mutants were nearly as sensitive to movobiocin, fusidic acid, erythromycin, rifampin and clindamycin as are deep rough (heptoseless) mutants; in addition, they were sensitive to methicillin, penicillin (to which heptoseless mutants are resistant), gentian violet, and anionic and cationic detergents. Class A and C mutants had less sensitive, but characteristic phenotypes. None of the 3 classes were sensitive to serum bactericidal action. The class B mutation mapped between map positions 7 and 11 on the S. typhimurium chromosome, and the class C mutation mapped between positions 5 and 7. The map position for the class A mutation remained undefined, but it was separate from the class B and C mutations and, like those, did not correspond to any gene loci known to participate in the synthesis of major outer membrane constituents.