PhD Defence by Amalia Bogri

Principal supervisor:

• Professor Frank M. Aarestrup, DTU Food

Co-supervisors:

• Associate Professor Christian Brinch, DTU Food
• Assistant Professor Saria Otani, DTU Food

Examiners:

• Senior Researcher Sara Monteiro Pires, DTU Food
• Professor Hanne Ingmer, Department of Veterinary and Animal
  Sciences, University of Copenhagen
• Professor Ville-Petri Friman, Department of Microbiology,
  University of Helsinki, Finland

Chairperson at defence:

• Senior Researcher Patrick Njage, DTU Food

Resume
Antimicrobial resistance is an increasing concern worldwide, largely due to the overuse of antibiotics in healthcare and agriculture. This PhD thesis examines the critical relationship between bacterial transmission and the development of antimicrobial resistance, offering new insights into this pressing issue.

The research is comprised of three key studies. The first utilizes a mathematical model to analyze how antibiotic use, the fitness cost of resistance, and bacterial transmission affect resistance levels in populations. This theoretical approach revealed various dynamics, including scenarios where increased bacterial transmission could unexpectedly lead to lower resistance.

In the second study, an in vitro experiment using Escherichia coli strains was conducted to evaluate the theoretical model. Results showed that the impact of bacterial transmission on resistance spread varies depending on the conditions of antibiotic use and the emergence of mutations, a new area explored in this thesis.

The final study introduces an innovative in vivo method using cockroaches to study resistance transmission. It found that tetracycline treatment changes the gut microbiome of these insects and resistance can spread to untreated populations through interaction, illustrating an important pathway for resistance transfer.

Overall, this thesis contributes to a better understanding of the interactions between bacterial transmission and antimicrobial resistance. It highlights the importance of considering both resistant and susceptible bacterial strains in developing strategies to address antibiotic resistance.