We recently described the use of selective transposon mutagenesis to generate a series of avirulent mutants of a pathogenic strain of Salmonella typhimurium. Cloning and sequencing of the insertion sites from two of these mutants reveals that both have identical locations within an open reading frame that is highly homologous to a gene, htrA, encoding a heat-shock protein in Escherichia coli. DNA sequence analysis of S. typhimurium htrA reveals the presence of a gene capable of encoding a protein with a calculated Mr of 49316 that has 88.7% protein:protein homology with its E. coli counterpart. In E. coli, lesions in this gene, also known as degP, reduce proteolytic degradation of aberrant periplasmic proteins. Characteristics of the S. typhimurium htrA mutants, 046 and 014, in vivo and in vitro suggested that they are avirulent because of impaired ability to survive and/or replicate in host tissues. In vitro, the S. typhimurium htrA mutants 046 and 014 are not temperature-sensitive but were found to be more susceptible to oxidative stress than the parent, suggesting that they may be less able to withstand oxidative killing within macrophages.

Background: The mechanism of nausea and vomiting associated with gastroenteritis is unknown. The role of 5‐HT3 receptors in emesis associated with gastroenteritis was investigated in paediatric patients. Methods: A randomized, double‐blind, placebo‐controlled, parallel‐group study was conducted in three groups of 12 patients each, receiving either a single i.v. dose of ondansetron (0.3 mg/kg), metoclopramide (0.3 mg/kg) or placebo (sterile saline). Food was restricted and oral rehydration was administered for 4 h. Results: During 0–24 h, the number of emetic episodes experienced was significantly greater (P=0.048) with placebo (mean=5) than ondansetron (mean=2) and the proportion of patients experiencing no emesis was significantly greater (P=0.039) with ondansetron (58%) than placebo (17%). A numerical difference, in favour of ondansetron, was observed between ondansetron and metoclopramide groups for both of the above parameters. Fewer treatment failures were observed with ondansetron (17%) than placebo (33%) and metoclopramide (42%). More diarrheal episodes were observed in the groups receiving anti‐emetic treatment. All three treatments were well tolerated. Conclusions: Ondansetron, a 5HT3 receptor antagonist, was significantly superior to placebo in preventing emesis associated with acute gastroenteritis, in paediatric patients. Therefore, serotonin, acting through 5HT3 receptors, may play a role in this form of emesis.

One hundred fifty TnS IS5OL::phoA (TnphoA) mutants of a mouse-virulent, nalidixic acid-resistant (Nat"), prototrophic Salmonella typhimurium strain, C5 Nalr, were isolated. None of the mutants were auxotrophs. Groups of 8 to 10 BALB/c mice were infected orally with each of 95 mutants with a dose equivalent to 20-fold the 50% lethal dose of the wild-type C5 Nalr strain, and deaths were counted over the next 28 days. Fifteen of the mutants failed to kill any mice, whereas all mice died following challenge with the other mutants. Nine of the 15 attenuated mutants exhibited a defect in lipopolysaccharide biosynthesis. The remaining six mutants were smooth. The TnphoA transposon of each of the smooth attenuated mutants was moved, using P22-mediated transduction, into a fresh C5 background, and all retransductants were still attenuated. Analysis of the membrane proteins of the attenuated mutants failed to reveal any alterations in detectable major outer membrane proteins, although colonies of two of the mutants exhibited a mucoid phenotype following growth on L-agar plates. Individual attenuated mutants differed in their abilities to translocate to livers and spleens of mice following oral infection. All of the smooth TnphoA mutants exhibited increased 50% lethal doses with respect to the wild type following intravenous infection of BALB/c mice. Southern analysis of DNA prepared from each of the mutants suggested that TnphoA had inserted into a number of different sites in the S. typhimurium genome. None of the TnphoA mutants had inserts in the virulence-associated plasmid.

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A cosmid gene bank of the virulent Salmonella typhimurium C5 was constructed in Escherichia coli K12. The bank was repackaged into bacteriophage heads and transduced into the semi-rough S. typhimurium strain AS68 which expresses the LamB lambda receptor protein. Approximately 6000 ampicillin-resistant transductants were pooled and used as host for the propagation of bacteriophage P22. The P22 lysate was able to transduce cosmid recombinants to smooth strains of S. typhimurium and individual transductants were selected which complemented various S. typhimurium auxotrophic mutations. A stable mutation was introduced into the aroD gene of S. typhimurium C5. The resulting aroD- mutant, named CU038, was highly attenuated compared with the wild-type parent strain and BALB/c mice immunised orally with CU038 were well protected against challenge with the virulent C5 parental strain. Using the cosmid bank repackaged into bacteriophage P22 heads it was possible to isolate cosmid recombinants that could complement the aroD mutation of CU038 either by in vitro selection using minimal medium or in vivo selection for restoration of virulence in BALB/c mice. Repackaged P22 cosmid banks could provide a simple system for selecting in vivo for Salmonella virulence determinants. A Salmonella typhi strain harbouring mutations in aroA and aroD was constructed for potential use as a live oral typhoid vaccine in humans.