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The virulence of trimethoprim-resistant thymine-requiring strains of Salmonella
Abstract:
A thymine-requiring (thy-), trimethoprim-resistant (tmpr) mutant isolated from the faeces of chickens experimentally infected with salmonella typhimurium and treated with mixture of trimethoprim and sulphadiazine was less virulent for chickens than the parent strain and a thy+tmps revertant prepared in vitro from the mutant. The difference in chicken-virulence was more noticeable when the strains were administered orally than when they were administered subcutaneously. All tmpr mutants prepared in vitro from four other salmonella strains were also thy-; those tested were less virulent for chickens and mice than their parent strains. After oral infection, thy- salmonella organisms were found much less commonly in the alimentary tract of chickens then were thy+ organisms. This was especially so in the caeca, the principal site of colonization of both the thy+ and thy- organisms. Relatiely high concentrations of thymine or related compounds were found in the contents of all regions of the alimentary tract of chickens except the caeca; the caeca usually contained low or undetectable concentrations. The thy- salmonella strains would not grow on one brand of briliant green agar because of its deficiency in thymine; their colonial and appearance on other kinds of media used for isolating salmonellae from clinical material was often 'un-salmonella-like'.
Insights
A thymine-requiring (thy-) Salmonella Typhimurium mutant showed reduced virulence in chickens. This thymine deficiency impacted bacterial colonization in the chicken gut, particularly in the ceca.
Area of Science:
- Microbiology
- Animal Science
- Genetics
Background:
- Salmonella Typhimurium is a significant pathogen in poultry.
- Antibiotic resistance, such as trimethoprim resistance (tmpr), is a growing concern in bacterial infections.
- Nutritional auxotrophy can impact bacterial virulence and colonization.
Purpose of the Study:
- To investigate the virulence and colonization characteristics of a thymine-requiring (thy-) Salmonella Typhimurium mutant in chickens.
- To compare the virulence of the thy- mutant with its parent strain and a revertant.
- To explore the role of thymine availability in the chicken gut on Salmonella colonization.
Main Methods:
- Isolation of a thymine-requiring (thy-), trimethoprim-resistant (tmpr) Salmonella Typhimurium mutant from experimentally infected chickens.
- Virulence assessment in chickens via oral and subcutaneous administration of bacterial strains.
- Comparison of colonization levels of thy- and thy+ strains in the chicken alimentary tract, with a focus on the ceca.
- Analysis of thymine concentrations in different regions of the chicken gastrointestinal tract.
- Evaluation of the growth of thy- mutants on selective media.
Main Results:
- The thy- tmpr mutant exhibited significantly reduced virulence in chickens compared to the parent strain and a thy+ revertant.
- Oral administration led to more pronounced differences in virulence than subcutaneous administration.
- All in vitro generated tmpr mutants from other Salmonella strains were also thy- and showed reduced virulence in chickens and mice.
- Thy- Salmonella were found less frequently in the chicken alimentary tract, especially in the ceca, compared to thy+ strains.
- The ceca consistently showed low thymine concentrations, unlike other gut regions.
- Thy- mutants displayed altered colonial morphology and poor growth on thymine-deficient media.
Conclusions:
- Thymine auxotrophy significantly attenuates Salmonella virulence in avian hosts.
- The availability of thymine in the host's gastrointestinal tract is crucial for Salmonella colonization, particularly in the ceca.
- The thy- phenotype can affect bacterial detectability and appearance on diagnostic media, potentially impacting clinical isolation.