| Project Detail |
Rationale of the study: Antibiotic resistance is the most prominent issue tackled by One Health, an interdisciplinary approach involving human and veterinary medicine as well as environmental science. Chlamydia (C.) suis is endemically present in the fattening pig population worldwide and zoonotic transmission events are possible. C. suis is the only chlamydial species to date which has acquired antibiotic resistance, to tetracycline (Tet). Transfer of the Tet resistance determinant among C. suis is facilitated by homologfgous recombination and is promoted by selective pressure in pigs (oral antibiotic treatment). However, it remains unclear how this obligate intracellular bacterium can take up Tet resistance determinants (Uptake). Further knowledge gaps exist on how the porcine gastrointestinal tract (GIT) serves as a reservoir for these strains and how Tet resistant (TetR) strains are promoted within the GIT (Reservoir). It is known that resistance determinants can spread in the environment via manure, however, no data is available on how common this event is for the Tet resistance determinant originating from the obligate intracellular bacterium C. suis (Spread).Preliminary data: Previously, we have shown that C. suis is ubiquitous in Swiss fattening pigs and that circulating strains show a high genetic diversity locally and globally. The TetR determinant is integrated into the C. suis chromosome, can be transferred to other chlamydial species and TetR strains are enhanced by selective pressure. The porcine GIT is the site of endemic infection and potential resistance transfer. We have successfully established fluorescent C. suis strains by transforming them with fluorescent markers, which allows us to perform and analyze more complex in vitro experiments.Hypotheses: We hypothesize that: (i) uptake of DNA-containing extracellular vesicles (EV), vesiduction, is a horizontal gene transfer (HGT) mechanism by which Tet sensitive (TetS) C. suis strains can acquire the Tet resistance determinant; (ii) two different strains frequently infect the same cell forming separate inclusions which merge into one inclusion by fusion over the course of the chlamydial developmental cycle; (iii) the porcine GIT simultaneously harbors a diversity of TetR and TetS strains; (iv) TetR strains outcompete TetS strains when tetracycline selective pressure is applied, but TetS strains dominate in the absence of tetracycline or in the presence of trimethoprim/sulfonamide compounds; (v) Tet resistance determinants of C. suis are present in liquid manure; and (vi) TetR and TetS C. suis remain viable in liquid manure.Aims of the project: We aim to determine the role of vesiduction in the uptake of the Tet resistance determinant in C. suis, the frequency with which two separate C. suis strains co-infect the same cell as well as the extent to which these separate inclusions fuse with each other (Aim 1, Uptake). Furthermore, we aim to investigate whether the porcine GIT simultaneously harbors a diversity of TetR and TetS strains with an increased ratio of TetS strains, and whether TetR strains outcompete TetS strains when antibiotic selective pressure is applied (Aim 2, Reservoir). Lastly, we aim to test whether Tet resistance determinants of C. suis are detectable in liquid manure and if, and how long, TetR C. suis can remain viable potentially contaminating the environment (Aim 3, Spread).Expected results and impact: Our project will contribute to the understanding of TetR C. suis concerning Tet resistant determinant uptake and transfer, the GIT as a reservoir, and spread in the environment. This is important to know when developing surveillance and prevention strategies in agriculture (pig farming) and the environment. Our data will also facilitate the development of strategies to monitor and prevent further selection/dissemination of TetR chlamydial strains in pigs and humans. The knowledge gain of the proposed studies includes: i) application to the One Health field, in particular to antibiotic resistance and zoonotic infection in chlamydiae (Chlam Health), ii) following the path of Tet resistance from the cellular level to the environment, iii) using C. suis as a model organism to learn more about antibiotic resistance menchanisms in obligate intracellular bacteria, iv) assessing the risk of TetR acquisition by HGT from C. suis to other chlamydiae, and v) to refine the first existing transformation system for C. suis (the only chlamydial species currently harboring stable homotypic resistance) available in the Chlamydia research field. |
