Cross-reactive immune response induced by the Vi capsular polysaccharide typhoid vaccine against Salmonella Paratyphi strains.

There are no vaccines in clinical use against paratyphoid fever, caused by Salmonella Paratyphi A and B or, rarely, C. Oral Salmonella Typhi Ty21a typhoid vaccine elicits a significant cross-reactive immune response against S. Paratyphi A and B, and some reports suggest cross-protective efficacy against the disease. These findings are ascribed to the O-12 antigen shared between the strains. The Vi capsular polysaccharide vaccine has been shown to elicit antibodies reactive with O-9,12. Twenty-five volunteers immunized with the parenteral Vi vaccine (Typherix(®) ) were explored for plasmablasts cross-reactive with paratyphoid strains; the responses were compared to those in 25 age- and gender-matched volunteers immunized with Ty21a (Vivotif(®) ). Before vaccination, 48/50 vaccinees had no plasmablasts reactive with the antigens. Seven days after vaccination, 15/25 and 22/25 Vi- and Ty21a-vaccinated volunteers had circulating plasmablasts producing antibodies cross-reactive with S. Paratyphi A, 18/25 and 23/25 with S. Paratyphi B and 16/25 and 9/25 with Paratyphi C, respectively. Compared to the Ty21a group, the Vi group showed significantly lower responses to S. Paratyphi A and B and higher to S. Paratyphi C. To conclude, the Vi vaccine elicited a cross-reactive plasmablast response to S. Paratyphi C (Vi antigen in common) and less marked responses to S. Paratyphi A and B than the Ty21a preparation. S. Paratyphi A and B both being Vi-negative, the result can be explained by trace amounts of bacterial cell wall O-12 antigen in the Vi preparation, despite purification. The clinical significance of this finding remains to be determined.

Serodiagnosis of Salmonella enterica serovar Typhi and S. enterica serovars Paratyphi A, B and C human infections.

The aim of this study was to evaluate an immunoassay for the detection of human serum antibodies to the LPS and flagellar antigens of Salmonella Typhi and Salmonella Paratyphi A, B and C, and to the Vi capsular polysaccharide of S. Typhi and S. Paratyphi C. A total of 330 sera were used; these originated from 15 patients who were culture-positive for S. Typhi and 15 healthy controls, together with 300 sera submitted to the Laboratory of Enteric Pathogens for Salmonella serodiagnosis. By SDS-PAGE/immunoblotting, all 15 sera from culture-positive patients had serum antibodies to the 9,12 LPS antigens and 10 had antibodies to the 'd' flagellar antigens. Of the 300 reference sera, 22 had antibodies to the 9,12 LPS antigens, one to the 1,4,5,12 LPS antigens and 12 to the 6,7 LPS antigens. Only two sera had antibodies to flagellar antigens, one of which bound to the 'b' and the other to the 'd' antigen. An ELISA was developed that successfully detected serum antibodies to the Vi capsular polysaccharides, but because of the kinetics of serum antibody production to the Vi, these antibodies may be of limited value in the serodiagnosis of acute infection with S. Typhi and S. Paratyphi C. The immunoassays described here provide a sensitive means of detecting serum antibodies to the LPS, flagellar and Vi antigens of S. Typhi and S. Paratyphi, and constitute a viable replacement for the Widal assay for the screening of sera. The Salmonella serodiagnosis protocols described here are the new standard operating procedures used by the Health Protection Agency's National Salmonella Reference Centre based in the Laboratory of Enteric Pathogens, Colindale, UK.

Characterization of the Salmonella paratyphi C Vi polysaccharide.

The Vi capsular polysaccharide (Vi) is both a virulence factor and a protective antigen of Salmonella typhi; its pathogenic role for Salmonella paratyphi C is less well understood. We found no differences between the antigenic and immunogenic properties and the structure of the Vi from representative strains of S. paratyphi C, S. typhi, and Citrobacter freundii. There were, however, differences in both the amount produced per cell and the degree of association with the cell among the Vi from the three species of Enterobacteriaceae. S. paratyphi C produced less Vi than both the wild-type S. typhi and C. freundii did, and it showed the fastest release of Vi into the media. These findings may provide an explanation for the inability of the Vi to inhibit completely the agglutination of S. paratyphi C by anti-O sera. In an outbreak of enteric fever caused by S. paratyphi C, 66 of 78 isolates (85%) were Vi positive.

Specific proteins common to Salmonella paratyphi B and C.

A serum prepared with proteins from Salmonella paratyphi C precipitates indiscriminately the proteins from numerous heterologous Salmonellae. After different absorptions, that eliminate all the antibodies induced against common E. coli and Salmonellae determinants, a specific precipitation of a S. paratyphi C protein which is identical with that of an S. paratyphi B protein is evident in agar gel diffusion.

Brucellosis in man. I. Serological diagnosis.

50 Blood samples were collected from in-patients with febrile splenomegaly suspected to be Malta fever, in Sharkia fever hospitals; Egypt. The samples were subjected to serological tests (tube agglutination, Widal & Coombs) for diagnosis of brucellosis. The results of tube agglutination (TAT) revealed that 5 (10%) were positive; the titre ranging from 1/80-1/320, 3 doubtful (1/40) and 42 negative (1/20, 1/10 and no agglutination). Results of the Coombs test on negative and doubtful of TAT showed that out of 45 patients; 3 (6.66%) were positive; the titre ranging from 1/80-1/160, one doubtful and 41 negative. Coombs test improved the titre of one positive case of TAT from 1/320-1/640. Results of serological tests (TAT & Coombs) for MALTA fever were 8 (16%); the titre ranging from 1/80-1/640, one doubtful (1/40) and 41 negative. Results of the Widal test to detect Enteric fever in the way of differential diagnosis were 7 (14%) positive out of 50 patients examined; the titre ranging from 1/80-1/160. Five of them agglutinated typhoid (O&M) suspensions. One of the sera agglutinated paratyphi A (H) suspension, the remaining one serum agglutinated paratyphi. B(H) suspension and none of the sera agglutinated paratyphi. C(H) suspension. All the positive Coombs and negative Widal cases were obtained against typhoid (O) suspension and none against any of the (H) suspensions; Coombs test was positive in two (4.65) of 43 patients negative to Widal; no improvement of titre in the positive Widal. Results of Widal & Coombs to detect Enterica were 9 (18%) positive and 41 negative.

[Active immunization to experimental salmonellosis in mice protective properties of Salmonella R mutants against infection with different pathogenic Salmonella species (author's transl)]. / Aktive Immunisierung gegen experimentelle Salmonellose in der Maus Die Wirksamkeit von Salmonella-R-Mutanten unterschiedlicher Herkunft gegenüber Infektionen mit verschiedenen Salmonella-Spezies.

Mice (NMRI) were immunized twice with acetone-killed bacteria from 13 different Salmonella R-mutant and 6 Salmonella S form strains. Of the R mutants one strain was a semirough mutant, 9 strains belonged to the chemotype Ra, one to chemotype Rb2 and 2 to chemotype Re. Of the S forms 2 strains derived from serological group B, 2 from group D1 and one strain from each of group C1 and C2. Ten days after immunization the animals were challenged with increasing numbers of S-form bacteria (the same S strains as those used for immunization) administered intraperitoneally. The virulence (LD50) of the strains used was between 6 x 10(2) and 3 x 10(5) cells. The results show that every mutant was capable of affording protection to the S-form bacteria used, i.e. the protection was not confined to the species used for immunization; nevertheless differences in the degree of protection were present. These differences were found both in the ability of the different mutants to protect towards the same infecting microorganism and in the protection obtained by individual mutants towards infection with the different S-forms. With certain strains a relatively high degree of protection was obtained, with others the protection was low compared to that seen with homologous S form vaccines. In infection with s. typhimurium, unlike infection with other S-forms, the homologous R mutants were superior to the other mutants in their immunizing properties. Immunization with heterologous S-forms yielded similar results as those obtained with R mutants. S-forms with identical O-antigens were not necessarily comparable in their protective properties. Although the protective effect of R mutants was generally lower than that produced by homologous S-form vaccines, the present results show that in a few cases an equally high protection may also be obtained by R mutants. The present results lead to the conclusion that the cell-surface of Salmonella contains, in addition to the known antigens, other components playing an important role in inducing immunity to infection. A partial divergence in the pattern of such components among the different vaccines, would explain the extension of immunity obtained by the heterologous species also.

Behaviour of S. paratyphi A in mice immunized with homologous and heterologous bacterial proteins.

Mice immunized with proteins from S. typhimurium and from S. paratyphi C resisted the toxicity of a concentration of S. paratyphi A which killed the controls; this is in contrast to the results found in mice immunized with the same amount of proteins from the homologous S. paratyphi A. For the neutralization of the S. paratyphi A toxicity a higher quantity of homologous proteins was necessary in the immunizations. It is assumed that either S. paratyphi A synthesizes--on artificial media--a small amount of proteins responsible for the induction of neutralizing antibodies or that it is an intrinsic weak immunogen. In the sera of mice in which sufficient neutralizing antibodies were induced, the proteins of S. paratyphi A cross-reacted in agar-gel, with the proteins from S. typhimurium and from S. paratyphi C.

Immunochemical relations of salmonella paratyphi C with the salmonellae of group B.

Agar-gel precipitations of proteins from S. paratyphi C, S. paratyphi B and S. typhimurium against homologous and heterologous antibacterial sera, prepared in rabbits, demonstrated a strong relatedness between these species belonging to different serogroups. The findings explain and substantiate previous experiments in which high cross-protections were obtained in groups of mice immunized with proteins from these species and subsequently infected with S. typhimurium or its "in vivo" related S. paratyphi B and S. paratyphi C.

Genetic basis of Vi antigen expression in Salmonella paratyphi C.

Analysis of hybrids formed in a cross between a Salmonella paratyphi C Hfr and an S. typhimurium recipient indicated that the structural genetic determinants of the S. paratyphi C Vi antigen are located closely adjacent to the mel determinant, between this marker and purA. A similar location was indicated for the structural genetic determinants of the S. typhi Vi antigen (the viaB locus) by the results of a mating in which a hybrid S. typhimurium Hfr bearing the S. typhi viaB determinants was used to transfer these genes to an S. typhimurium recipient. Mating experiments with a Vi-antigen-expressing S. typhi Hfr and an S. typhimurium hybrid recipient expressing the Vi antigen of S. paratyphi C yielded no recombinants in which loss of Vi antigen expression occurred, indicating that the chromosomal locus occupied by the genetic determinants of the S. paratyphi C Vi antigen is the same one at which, in S. typhi, the viaB genes reside. Introduction of a mutant S. typhi viaA gene into an S. typhimurium hybrid expressing the Vi antigen, as the consequence of prior receipt of the S. paratyphi C viaB determinants, resulted in that hybrid's loss of Vi antigen expression, demonstrating that the viaA determinant plays a role in Vi antigen expression in S. paratyphi C, as well as in S. typhi. Although the percentages of coinheritance of the viaB and mel determinants in the mating experiments suggested that their linkage is sufficiently close to allow cotransduction by P22, attempts to accomplish this with lysates prepared on S. typhimurium hybrids expressing either S. typhi or S. paratyphi C viaB determinants were not successful.

Cross-protection induced in mice by immunizations with proteins of related bacteria species.

Groups of mice were immunized with detoxified protein from S. typhimurium, S. paratyphi B and S. paratyphi C. Consecutive infections with different concentrations of the homologous and heterologous strains showed that: 1. Immunizations with proteins from S. typhimurium induced protections in 65% of the mice infected with 50 LD100 of their natural pathogen, and in 80% of the mice infected with 50 LD100 of S. paratyphi B; the infection with S. paratyphi C of mice in this group afforded protection against 20 LD100 in 75% of the animals. 2. Immunization with proteins from S. paratyphi B induced protection in the mice against the infection with 20 LD100 of S. typhimurium (survival of 80% of the mice) and against 20 LD100 of the homologous S. paratyphi B (survival of 90% of the mice). 3. Immunization with proteins from S. paratyphi C protected the mice against the infection with 20 LD100 of S. typhimurium in a proportion of 80-85% of the animals; infection with the homologous S. paratyphi C did not result in protection against more than 20 LD100 of the bacteria (80-85% survivals). The survivors, in each group, when reinfected 30 days later with 50 LD100 of S. typhimurium resisted in a proportion of 100%, as a consequence of antibodies induced against more specific proteins released in the mice during the infections by the related pathogens.

Heterologous protections in experimental salmonellosis.

Immunizations of mice with proteins from S. paratyphi B protected the animals against infection with a concentration of S. paratyphi C which killed the controls and against an infection with 50 LD100 of the homologous S. paratyphi B. The sera of the infected mice showed common precipitation lines of proteins from the two species belonging to different serogroups. Consecutive inoculations with S. typhimurium of both groups of vaccinated mice protected the animals against the infection with their natural pathogen. Immunizations with proteins from S. cholerae-suis protected about 70% of the mice infected with S. paratyphi B and with S. paratyphi C; a higher protection was not, however, induced against infection with the homologous strain. Consecutive infections with S. typhi-murium of the mice resulted in total protection of the animals previously inoculated with S. paratyphi B and S. paratyphi C; the group of mice infected with S. cholerae-suis was less protected against the subsequent inoculation with S. typhi-murium (about 50%). In the infections of mice, S. paratyphi B and S. paratyphi C, seem related to S. typhi-murium by common proteins; the proportion of common protective determinants is not yet known.