PhD thesis defense in biological sciences by Thomas Rouma

Characterization of Experimental Acinetobacter baumannii Lung Infection in Mice: Therapeutic Strategies, and Vaccine Development

Candidate

Thomas Rouma

Promoters

Prof. Xavier De Bolle, UNamur, Department of biology, Research Unit in Biology of Microorganisms (URBM) - promoter

Prof. Eric Muraille, Laboratoire de Parasitologie, ULB - co-promoter

Jury

• Prof. Xavier De Bolle, UNamur (promoter)
• Prof. Eric Muraille, ULB (co-promoter)
• Prof. Régis Hallez, UNamur 
• Prof. Anne Botteaux, ULB
• Prof. Laurence Van Melderen, ULB
• Arnaud Machelart, Univ. Lille 
• Olivier Denis, Sciensano 

Summary

Acinetobacter baumannii is an opportunistic pathogen responsible for severe nosocomial infections, whose management is complicated by its multidrug resistance to antibiotics. This thesis aims to better understand the interactions between A. baumannii and the immune system during pulmonary infection in mice, and to leverage this knowledge to develop new therapeutic and vaccination strategies.

We characterized the localization of A. baumannii in the lungs of infected mice using electron microscopy and flow cytometry. Alveolar macrophages and neutrophils were the main cell populations internalizing bacteria. When infection control was compromised, A. baumannii primarily proliferated extracellularly within the pulmonary connective tissue.

We showed that dimethyl itaconate (DMI), a derivative of itaconate produced by the enzyme ACOD1 in alveolar macrophages, inhibits the growth of several A. baumannii strains in vitro at neutral pH. However, neither ACOD1 deficiency nor exogenous administration of DMI significantly altered the course of infection or the associated immune response.

We also demonstrated that intranasal vaccination with a heat-killed whole-cell vaccine (HK) effectively protected mice against pulmonary infection with the hypervirulent LAC-4 strain, including in several immunodeficiency models. This protection was primarily mediated by antibodies targeting bacterial capsule-associated antigens. We subsequently developed a whole-cell vaccine based on encapsulation of bacteria within a metal-organic framework (MOF). This vaccine provided better control of systemic dissemination than the HK vaccine and induced a robust humoral response. A multivalent formulation combining several clinical strains broadened antibody recognition while maintaining protection against different strains.

In contrast, an approach based on an RNA subunit vaccine targeting several surface antigens failed to provide significant protection against A. baumannii infection.

Overall, this thesis highlights the importance of characterizing the in vivo interactions between A. baumannii and the immune system. It demonstrates the major role of alveolar macrophages and neutrophils in the early response to infection, as well as that of humoral immunity in vaccine-mediated protection. Finally, it demonstrates the potential of whole-cell vaccines, particularly in multivalent formulations, for the development of preventive strategies against A. baumannii infections.