Humanized mice are susceptible to Salmonella typhi infection

Salmonella enterica serovar Typhi is a pathogen that only infects humans. Currently, there is no animal model for studying this pathogen. Recently, alymphoid RAG-2(-/-)/γ(c)(-/-) mice engrafted with human leukocytes, known as humanized mice, have been successfully utilized to develop experimental models for several human-specific viral infections, including HIV, human-like dengue fever and hepatitis C virus. Little is known about the usefulness and feasibility of the humanized mouse model for the study of human-specific bacterial pathogens, such as S. typhi. The aim of this study was to determine if Salmonella enterica serovar Typhi could establish productive infection in humanized mice. Here we report that intravenous inoculation of S. typhi into humanized mice, but not controls, established S. typhi infections. High bacterial loads were found in the liver, spleen, blood and bone marrow of mice reconstituted with human leukocytes, but not in the unreconstituted control mice. Importantly, S. typhi-infected humanized mice lost significant body weight, and some of the infected mice displayed neurological symptoms. Our data suggest, for the first time, that humanized mice are susceptible to S. typhi challenge and that this model can be utilized to study the pathogenesis of S. typhi to develop novel therapeutic strategies.     

An unusual post-operative wound infection with Salmonella typhi: case report

A 25 year old male student presented with a discharging sinus and swelling over right forearm, which on culture yielded S. typhi, sensitive to Ciprofloxacin. Predisposing factors were absent but there was a history of surgery for chronic osteomyelitis of right ulna and injury with cricket ball at same site. Pus obtained during surgery was sterile. Patient responded to oral Ciprofloxacin. Soft tissue infections are uncommon manifestation of salmonellosis. This case is an unusual presentation of post-operative Salmonella typhi wound infection.     

Innate resistance of mice to Salmonella typhi infection.

The basis for the natural resistance of mice to Salmonella typhi was examined. In contrast to Salmonella typhimurium, the virulence of S. typhi for mice was independent of the mouse strain and was not affected by inactivation of murine macrophages with silica. However, mice were more susceptible to S. typhi when given iron alone or iron and an iron chelator. The results suggest that the failure of S. typhi to undergo net growth in murine tissues reflects an inability of the bacterium to multiply rather than rapid killing by resident macrophages.     

Protection against Salmonella typhi infection in mice after immunization with outer membrane proteins isolated from Salmonella typhi 9,12,d, Vi.

The current studies were undertaken to assess the ability of the outer membrane proteins (OMPs) of Salmonella typhi to induce protection against challenge with the bacteria in mucin. OMPs were isolated as described by Schnaitman (J. Bacteriol. 108:553-556, 1971) and were found to be contaminated with approximately 4% lipopolysaccharide (LPS). Immunization with as little as 30 micrograms of OMPs conferred 100% protection to mice challenged with up to 1,000 50% lethal doses (LD50) of two strains of S. typhi (9,12,d, Vi and Ty2). In addition, 30% protection against challenge with up to 500 LD50 of Salmonella typhimurium was achieved. Immunization with LPS at doses equivalent to those found in the OMPs was considerably inferior to the OMPs in the induction of an immune status. Moreover, LPS was effective only when the challenge was performed with S. typhi 9,12,d, Vi (40% protection to 100 LD50). An antiserum raised in rabbits reacted mainly against the bands of the molecular weights corresponding to the so-called porins contained in the OMP preparation as shown by Western blotting (immunoblotting). This rabbit antiserum protected 100% of mice against challenge with 100 LD50 of either strain of S. typhi and 80% of mice against challenge with the same LD50 of S. typhimurium. These results indicate the usefulness of OMPs in the induction of active immunity against S. typhi in mice.     

Experimental Salmonella typhi infection in the domestic pig, Sus scrofa domestica

The domestic pig, Sus scrofa domestica, was examined as a model for typhoid fever, a severe and systemic disease of humans caused by Salmonella typhi. Six pigs were inoculated 1 week post-weaning with approximately 10(10)colony forming units (cfu) of wild type Salmonella typhi strain ISP1820 intranasally and observed for 3 weeks. S. typhi was cultured from the tonsils of 50% of the pigs at necropsy. Cultures from all other organs analysed (ileum, colon, spleen and liver) were negative. No clinical or histopathological signs of disease were observed. Pigs inoculated in parallel with swine-virulent S. choleraesuis all exhibited signs of systemic salmonellosis indicating that the parameters of the experimental infection with S. typhi (e.g. route) were appropriate. Whereas the pig has a gastrointestinal tract that is very similar to humans, our results indicated that the unique features of host and microbe interaction needed to produce typhoid fever were not mimicked in swine. Nevertheless, our observation of tonsillar involvement was consistent with former observations of S. choleraesuis and S. typhimurium infections in swine and supports a role for the tonsil in all porcine salmonella infections.     

Serological response of patients infected with Salmonella typhi.

AIMS: To evaluate a rapid immunoblotting procedure for providing evidence of infection with Salmonella typhi using 73 sera from patients infected with S typhi. METHODS: A sodium dodecyl sulphatepolyacrylamide gel electrophoresis (SDS-PAGE)/immunoblotting procedure using lipopolysaccharide (LPS, O = 9,12) and flagellar (H = d) antigens was used. RESULTS: Seventy two of 73 sera contained antibodies to LPS, 40 sera also contained antibodies to H = d flagellar antigens. Analysis of acute and convalescent sera showed that only 62% of patients produced antibodies to flagellar antigens. CONCLUSIONS: The SDS-PAGE/immunoblotting procedure provided a rapid method for providing serological evidence of infection with S typhi.     

A steady decrease in occurrence of Salmonella typhi infection in Rourkela, Orissa

Between January 1999 and December 2001, the isolation rate of Salmonella typhi in Rourkela was found to be under steady fall as compared to the isolation rate encountered between 1996 and 1998. Of 4378 blood samples tested, 254 were found positive for S. typhi giving an over all per cent positivity of 5.8. Enteric fever was found to occur almost through out the year. An over all 30.7 per cent of multi drug resistant (MDR) strains of S. typhi have appeared during this period. Proper and timely health education besides undertaking corrective measures in sanitary system and water supply management, appeared to have a cumulative effect in the steady reduction of enteric fever morbidity in this region.     

Significance of Salmonella typhi bacteriuria.

Bacteriuria due to Salmonella typhi usually occurs following recent typhoid fever or in chronic carrier states. Data from 18 patients with S. typhi bacteriuria, seen during 5 years, were analyzed. Fourteen patients had localized urinary tract infection due to S. typhi. Four others had bacteriuria, probably associated with typhoid fever. Localized abnormalities of the urinary tract and kidneys and also systemic diseases were found to predispose patients to S. typhi bacteriuria. Local abnormalities encountered included urolithiasis (n = 3), prostatic hypertrophy (n = 1), and tuberculosis (n = 1). One renal transplant recipient and another with lupus nephritis had S. typhi bacteriuria. One had associated strongyloidosis, and another was pregnant.     

Characterization of a phase 1-d epitope on Salmonella typhi flagellin and its role in the serodiagnosis of typhoid fever.

A monoclonal antibody (MAb) directed against Salmonella typhi 52 kDa flagellin protein has been previously produced by our group. In this study, we have demonstrated that the epitope specific to the MAb is unique to phase 1-d. To map the epitope, plasmids encoding different regions of S. typhi flagellin gene were constructed. Analysis of protein produced from each recombinant plasmid indicated that the epitope specific to the MAb resided within amino acids 171-303 (region IV) of S. typhi flagellin protein. The recombinant region IV flagellin was used to develop an ELISA for the detection of IgM antibody to S. typhi in serum. In the hemoculture-positive typhoid group, the developed ELISA was positive in 77 of 92 cases. In patients with non-typhoidal Salmonella, gram-positive and gram-negative bacteria or dengue virus, the ELISA was negative in all 78 cases. Two from 116 healthy control subjects had positive reactions with the assay. The calculated sensitivity, specificity, positive and negative predictive values of the test were 83.7%, 99.0%, 97.5% and 92.8%, respectively. With such high validity together with the requirement of only a single serum specimen and one day for performing the test, the developed ELISA should become a valuable diagnostic test for typhoid fever.     

Antibodies to porin antigens of Salmonella typhi induced during typhoid infection in humans.

To determine whether lipopolysaccharide (LPS) structures of Campylobacter fetus are related to the three known heat-stable serogroups, proteinase K-treated whole cell lysates obtained from strains of each serogroup were electrophoresed in polyacrylamide gels. All strains had smooth-type LPS with multiple high-molecular-weight repeating units. The profiles of serogroup A from C. fetus subsp. fetus and from C. fetus subsp. venerealis were identical, but they were different from those of C. fetus subsp. fetus serogroups B and AB. When we immunoblotted the LPS of these serogroups with normal or immune rabbit serum we found homologous recognition between serogroups A from C. fetus subsp. fetus and C. fetus subsp. venerealis. Similarly, serogroups AB and B from C. fetus subsp. fetus showed homologous recognition. However, antiserum against serogroup A did not recognize serogroups B and AB and vice versa. Absorption studies confirmed the identity of LPS from all serogroup A C. fetus strains and cross-reactivity of the serogroup B and AB strains with one another. Serogroup A strains were resistant to the bactericidal activity in normal human serum, whereas serogroup B and AB strains generally were susceptible; isolates from humans predominantly belonged to serogroup A. Results of these studies suggest that the LPS composition forms the basis for the heat-stable serotyping system for C. fetus and that the structural and antigenic variants are associated with differential serum susceptibility.     

Host restriction phenotypes of Salmonella typhi and Salmonella gallinarum.

Salmonella typhi and Salmonella gallinarum phenotypes correlated with mouse host restriction have been identified by using in vitro and in vivo systems. S. typhi is capable of entering the murine intestinal epithelium via M cells, as is Salmonella typhimurium, which causes systemic infection in the mouse. But, unlike S. typhimurium, S. typhi does not destroy the epithelium and is cleared from the Peyer's patches soon after M-cell entry. S. gallinarum appears to be incapable of entering the murine Peyer's patch epithelium. Our in vitro evidence suggests that S. gallinarum is taken up in murine phagocytic cells by a mechanism different from that of S. typhimurium. S. typhimurium is taken up at a higher frequency and is maintained at higher viable counts throughout a 24-h time course in a murine macrophage-like cell line than are S. gallinarum and S. typhi.