Relation of lipopolysaccharide character to P1 sensitivity in Salmonella typhimurium

Phage P1 clr (a variant of P1 kc), grown on an LT2 derivative so as to be appropriately modified, was tested for ability to produce plaques on numerous Salmonella typhimurium strains of different lipopolysaccharide (LPS) character: the rate of irreversible adsorption of P1 clr by representative strains was measured. It appeared that the P1-resistance of wild-type (i.e., smooth) S. typhimurium (and of some classes of rough mutant) results from failure to adsorb the phage. P1 clr plated efficiently only on the four LPS classes which are sensitive to phage C21 and make either galactose-deficient (classes galE and rfaH) or glucose-deficient incomplete core LPS (classes rfaG and galU). Rates of adsorption ≥ 40 > 10 −11/bacterium/min. were observed only for bacteria unable to make UDPgalactose, either by point mutation at galE or by deletion of the gal operon. A low, variable e.o.p. (usually 10 −5 to 10 −6 was obtained on mutants making complete core LPS, either without 0 chains (classes rfb, pmi, and rfaL) or with only single 0 units (class rfaF). Phage P1 clr had no detectable effect on smooth strains or mutants with various other LPS core defects. Phage P1 cm had the same host-range, except that it plated efficiently on some strains on which P1 clr plated with low and variable efficiency; it converted some P1-sensitive strains to chloramphenicolresistance, but the number of resistant colonies obtained was always less than the number of plaques produced. Phage P1 clr grown on E. coli K12 plated efficiently on galE, etc., derivatives of an LT2 line made restriction-negative by mutations at hspLT and hspS, but did not plate (e.o.p. < 10 −3) on LT2 galE wild-type for restriction.