O‐antigenic specificity of the protective supernatant factor from Salmonella typhimuvium effective in S. typhimurium‐infected mice

Abstract

A supernatant factor (SF) prepared from cultures of Salmonella typhimurium protected naturally susceptible inbred mice against challenge with S. typhimurium subcutaneously injected (s.c.i.), but not against Salmonella enteritidis, suggesting tha the relevant specificity involved lipopolysaccharide. Further experiments were performed with two transductant strains of S. typhimurium. Strain SH6701 has O-antigen 4 from S. typhimurium and SH6703 had O-antigen 9 from S. enteritidis. Immunization with SF from SH6701 protected 95% BALB/c mice challenged with 100 LD50 S. typhimurium s.c.i., whereas SH6703 immunization had no effect on survival or mean survival time. SH 6703 SF gave some protection against homologous challenge. Antibody titres and delayed-type hypersensitivity reactions were also tested in immunized mice. The SF was, therefore, specific in that O-antigen 4 was necessary to protect mice against S. typhimurium challenge. Since we have previously demonstrated protein to be necessary for protection by SF, the active factor may be in the form of a protein-lipopolysaccharide complex.

The protein‐lipopolysaccharide complex extracted with trichloracetic acid from Salmonella typhimurium effective in protection of mice against S. typhimurium infection

“…In view of these and previous results showing that specific LPS is necessary for effective immunization (Plant et al 1980) and the demonstration of protein in active fractions (Plant et al 1978), we have used a method to extract LPS from S. typhimurium which retained the protein in an active state (Staub 1965). This TCA-LPS preparation had advantages over the SF extracted previously (Plant et al 1978(Plant et al , 1980. The extraction procedure from large bulk cultures was more convenient.…”

“…The immunogens were prepared at the required concentrations in 0.2 ml saline and intraperitoneally injected (i.p.i.). The challenge dose of I O3 S. typhimuriurn was subcutaneously injected (s.c.i.j on day 3 1 (Plant, Glynn & Wilson 1978, Plant, Glynn & Valtonen 1980. The dose was equivalent to > 100 LDso for BALB/c mice (Plant & Glynn 1974).…”

“…Titres on day 31 after immunization of the mice with two doses of TCA-LPS were compared with control antibody levels. 0 and H antibodies were estimated by bacterial agglutination with live bacteria (Plant, Glynn & Valtonen 1980). Fixation of the H flagellar antigens by steaming the bacteria 1 h before use enabled measurement of 0 antibody levels alone.…”

“…They were found to be very similar (Figure 4) although SH6703 had a significant protein band missing, indicating perhaps that transduction procedures had altered the protein structure in the mutant TCA-LPS. No other obvious differences were apparent between SH6701 and SH6703 to account for their difference in protective ability (Plant, Glynn & Valtonen 1980).…”

“…This is the third in a series of papers (Plant, Glynn & Wilson 1978, Plant, Glynn & Valtonen 1980 defining the protective properties of extracted material from S. typhimurium cultures against S. typhimurium infections in mice. A supernatant factor (SF) prepared from 48-h bacterial growth in a simple salts medium protected normally TR I CH LOR A CETI c -A C I D EXTRA CTI O N or: LPS ( TC A -L PS) The LPS was extracted from cultures of S .…”