Mutations in Salmonella typhimurium Conferring Resistance to Felix O Phage without Loss of Smooth Character

Abstract

S U M M A R YSeveral mutants obtained from smooth SalmoneIla typhimurium strains by selection for resistance to Felix 0 (FO) phage [whose receptor site includes the N-acetylglucosamine branch of the lipopolysaccharide (LPS) core] were smooth in cultural properties, antigenic character and phage sensitivity pattern (except for their FO resistance). However, the affected genes of several such 'FOR' (FOresistant) mutants were shown by transduction to map in the short cysE-pyrE segment, which includes nearly all known rfa genes responsible for synthesis of LPS core. All of seven FOR mutants differed from their parents, and resembled rfa mutants with defects in the deeper part of the LPS core, by increased sensitivity to various antibiotics. One FOR mutant was non-virulent (LD,, > 107, compared with < IOO for its parent); L T~ derivatives given this FOR gene by co-transduction with cysE+ were likewise non-virulent. It is inferred that FOR mutations affect the assembly of the inner part of the LPS core, perhaps causing incomplete blocks in glycosyl transferase reactions. I N T R O D U C T I O NFelix 0 phage (hereinafter called FO) attacks nearly all smooth strains of Salmonella, whatever their 0 antigen, but is active on very few strains of Escherichia coli, etc. (Kallings, 1967). In Salmonella typhimurium it attacks not only smooth strains but also some nonsmooth mutants: those unable to transfer 0 chains from their site of synthesis to the 'complete' lipopolysaccharide (LPS) core, through mutation at rfaL or rfbT; the semirough (SR) class rfc, deficient in polymerization of 0 repeating units; and classes rfb and ymi, unable to synthesize 0 repeating units (Wilkinson, Gemski & Stocker, 1972). Phage FO, however, does not attack rfa mutants of various classes in which synthesis of the LPS core is defective. Lindberg and his colleagues (for review see Lindberg, 1973), from host range and from measurements of rates of adsorption by whole bacteria and of neutralization by isolated LPS, infer that the N-acetylglucosamine side-branch which is attached to the glucose I1 unit of the complete LPS core (Fig. I ) is an essential part of the adsorption site of FO phage. Most mutants selected from smooth strains by application of FO phage are of type [fa, with various sorts of defects in LPS core structure, and are recognizable as such by sensitivity to different combinations of rough-specific phages and/or to bile salts and by total or partial loss of 'smooth' cultural characters, 0 antigen(s) and sensitivity to smoothspecific phages (Wilkinson et a/. 1972). We here describe FO-resistant mutants of smooth * Present address :

Salmonella typhimurium Mutations Conferring Resistance to Felix O Phage without Loss of Smooth Character: Phage Attachment and Immuno-chemical and Structural Analyses of Lipopolysaccharides

“…MacPhee et al (1975) found that the FOR strain SL4504 was still virulent for mice, whereas SL4505 was not. The amount of LPS and the average length of 0 side-chain was virtually the same for the two FOR strains.…”

“…The FOR strains differ from their smooth parent strains primarily by being resistant to the FO phage, for in cultural and serological properties the FOR mutants were almost identical to the smooth strains (MacPhee et al 1975). This investigation was performed in order to try to analyse whether there were either qualitative or quantitative differences between LPS from FOR mutants and LPS from the parent strain, even if these could not be No LPS could be extracted from any of these strains by the PCP method.…”

“…repeating units and thus to have a side-chain of one repeating unit only, are FO sensitive (MacPhee et al 1975). It is inferred from this that the receptor for the FO phage is still synthesized in FOR strains but that access to it is hindered.…”

“…Salmonella typhimurium mutants, called Felix 0-resistant (FOR), selected for resistance to phage Felix 0 (FO) which has its receptor in the core lipopolysaccharide (LPS), retain most of the properties of the smooth parent strain (MacPhee, Krishnapillai, Roantree & Stocker, 1975). LPS extracted from one parent and two FOR strains by the phenol-water and the phenol-chloroform-light petroleum methods have been subjected to passive haemagglutination inhibition and methylation analysis.…”

“…A. D. Stocker, Department of Medical Microbiology, Stanford University. A description of the strains is given by MacPhee et al (1975). Each strain was re-isolated from a single colony and tested for nutritional characteristics and phage sensitivity.…”