Cathelicidins modulate the host immune response and the microbiota in Salmonella Typhimurium infection

• Author / Creator

  Bescucci, Danisa M

• Salmonella enterica serovar Typhimurium is a prevalent incitant of enteritis in human beings and swine. The historic use of antibiotics at non-therapeutic concentrations for growth promotion, and at therapeutic doses for group and individual treatment of pigs has been linked to development of antimicrobial resistance in Salmonella Typhimurium. This has resulted in restrictions on the use of antibiotics in swine production, necessitating the identification of non-antibiotic strategies to eliminate pathogens and mitigate their impact on the host (e.g. inflammation). It has been proposed that host defense responses incited by Salmonella allow the bacterium to overcome colonization resistance. To address this, piglets were orally inoculated with S. enterica serovar Typhimurium DT104, and the host responses and microbiota changes were temporally examined at the acute (2 days post-inoculation [dpi]), subacute (6 dpi), and recovery (10 dpi) stages of salmonellosis. At the acute stage of disease, body temperatures were elevated, and feed consumption and weight gain were reduced. Densities of Salmonella associated with mucosa decreased over time, with higher densities of the bacterium in the ileum and the large intestine. Moreover, substantive histopathologic changes were observed as a function of time, with prominent epithelial injury and neutrophil infiltration observed at 2 dpi. Correspondingly, a variety of host metrics were temporally affected in piglets with salmonellosis (e.g. TNFα, IFNγ, PR39, βD2, iNOS, IL8, REGIIIγ). The enteric microbiota was characterized using culture-independent and -dependent methods in concert, and taxon- and location-specific changes to the microbiota were observed in infected piglets. Bacteroides spp. (e.g. B. uniformis, B. fragilis), Streptococcus spp. (e.g. S. gallolyticus), and various Gammaproteobacteria were highly associated with inflamed tissues, while bacteria within Ruminococcaceae and Veillonellaceae were mainly associated with healthy mucosa. In conclusion, the findings showed that S. Typhimurium incited temporal and spatial modifications to the swine autochthonous microbiota, and to host defense responses, that were consistent with overcoming colonization resistance to incite salmonellosis in swine. This included upregulation of the cathelicidin and host defense peptide PR39.
  Host defense peptides, also known as antimicrobial peptides, have been shown to protect the host via a variety of mechanisms. In mice, the cathelicidin, murine cathelicidin-related antimicrobial peptide (mCRAMP) has been demonstrated to impair the proliferation of S. Typhimurium in vitro. However, the impact of mCRAMP on host responses and the microbiota following infection by this pathogen has not been determined. To address this, mCRAMP knockout mice (mCRAMP-/-) and wildtype mice (mCRAMP+/+) were administered the broad-spectrum antibiotic, streptomycin (ST+) or water alone (ST-). Furthermore, they were orally inoculated with S. Typhimurium DT104 (SA+) or buffer alone (SA-), and impacts on the host and enteric bacterial communities were temporally evaluated. Higher densities of the pathogen were observed in cecal digesta and associated with mucosa in SA+/ST+/mCRAMP-/- mice than in SA+/ST-/mCRAMP-/- mice at 24 hpi. Both SA+/ST+/mCRAMP-/- and SA+/ST-/mCRAMP-/- mice were more susceptible to infection exhibiting greater histopathologic changes (e.g. epithelial injury, leukocyte infiltration, goblet cell loss) at 48 hpi. Correspondingly, immune responses in SA+/ST+/mCRAMP-/- and SA+/ST-/mCRAMP-/- mice were affected (e.g. Ifnγ, Kc, Inos, Il1β, RegIIIγ). Systemic dissemination of the pathogen was characterized by metabolomics, and the liver metabolome was affected to a greater degree in SA+/ST+/mCRAMP-/- and SA+/ST-/mCRAMP-/- mice (e.g. taurine and cadaverine). Treatment-specific changes to the structure of the enteric microbiota were associated with infection and mCRAMP deficiency, with a higher abundance of Enterobacteriaceae and Veillonellaceae observed in infected null mice. The microbiota of mice that were administered the antibiotic and infected with Salmonella was dominated by Proteobacteria. The absence of mCRAMP was observed to modulate both host responses and the enteric microbiota enhancing local and systemic infection by Salmonella Typhimurium, implicating cathelicidin as an important regulator of salmonellosis. Given the protective role provided by cathelicidin, this HDP may be an effective therapeutic alternative to antibiotics for use against Salmonella enterocolitis. Moreover, the mCRAMP knockout model may advance elucidation of mechanisms of salmonellosis toward effective mitigation of this important disease.

• Subjects / Keywords

  • host defense peptides
  • Salmonella enterica Typhimurium
  • Cathelicidins

• Graduation date

  Fall 2020

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-ytng-wt48

• License

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