Salmonella typhimurium mutants of RfaH-phenotype: genetics and antibiotic sensitivities.

Transductional mapping, with phage ES18 or ES18.hl, showed that several mutations causing the RfaH- phenotype (defective formation of galactose I and also of more distal units of the lipopolysaccharide core) were located between metE and pepQ in the Salmonella typhimurium linkage map; the affected locus is designated rfaH. The mutation of one strain of RfaH- phenotype was located elsewhere, at an unidentified rfa locus. Introduction of an F' plasmid containing the metE segment of the Escherichia coli chromosome into several rfaH mutants restored the "smooth" (Rfa+) phenotype. Several rfaH mutations, and that of the phenotypically similar rfa mutant, caused increased sensitivity to bacitracin, polymyxin, novobiocin, nafcillin and oxacillin, as expected if the mutations have no effect on the formation of the part of the lipopolysaccharide core proximal to the galactose units.