-
Brucellosis is a widespread bacterial zoonosis leading to chronic forms. The group is interested in the molecular mechanisms of virulence allowing Brucella to adapt to its intracellular niche inside the macrophage. The events linked to the setup of the chronic phase of infection are analyzed under conditions of starvation and hypoxia mimicking the host environment. Direct application of these fundamental studies allows the development of original anti-bacterial agents.
Group manager : Stephan KÖHLER Phone : +33 [0]4 34 35 94 50
Research Team :
KÖHLER, Stephan ; group leader ; DR2
JUBIER-MAURIN, Véronique ; senior scientist ; CR1
LOPEZ, Marie ; CDD-IR
OCCHIALINI-CANTET, Alessandra ; university staff, scientist ; MCF
OUAHRANI-BETTACHE, Safia ; engineer ; IE2
HANNA, Nabil ; PhD student ("CBS2")
ABDOU, Elias ; PhD student
Brucellosis is the first bacterial zoonosis in the world and may be considered as an emerging disease in certain regions such as the Balkans. The causative agent of brucellosis, Brucella sp., is transmitted to man by direct contact with the infected animal, by uptake of contaminated foodstuff, or by the respiratory pathway. During the acute phase of infection, often characterized by undulant fever, the bacterium colonizes macrophage host cells
[Fig. 1 ; Fig. 2]. During the set-up of this phase, the pathogen uses a wide range of factors allowing him to adapt to this intracellular, a priori hostile, environment. In the absence of treatment, the disease may develop into chronic forms with the formation of abscesses or granulomas, difficult to cure. In order to better understand the strategies of infection of this bacterium and to propose novel, focused therapeutic approaches, our research subjects center on three main lines :
(1) The identification and the functional characterization of the Brucella factors necessary for replication inside the intramacrophagic niche ;
(2) The study of the adaptation of Brucella to conditions of starvation and hypoxia or anoxia, typically encountered during the chronic phase of persistent infection (several decades) ;
(3) The identification of novel therapeutic targets essential for the intracellular bacterial virulence as well as the development of anti-infectious agents effective during acute or chronic infection. Following the identification of the panel of B. suis genes (virulome) involved in the intramacrophagic replication of the pathogen (Köhler et al., PNAS 2002), our group has established the first quantitative proteomic profile of an intracellular bacterium (Al Dahouk et al., Proteomics 2008)
[Fig. 3]. These two stages of our research work have unravelled a strategy of metabolic adaptation of Brucella to the host cell environment. The work is at present completed by transcriptome analysis of Brucella within the macrophage. At this stage of infection, the pathogen encounters a nutrient-poor environment necessitating the induction of the stringent response. Furthermore, the later is essential for the expression of the Type-IV secretion system of Brucella (Dozot et al., Cell. Microbiol. 2006). In addition, within the vacuoles of circulating macrophages as well as in the target organs such as spleen and liver, the bacteria are located in a hypoxic environment. Studies of global gene regulation in Brucella due to stringent response and due to the adaptation to oxygen depletion are under way. The results obtained, notably the description of the intramacrophagic virulome of Brucella, were the starting-point for an alternative strategy aiming at the development of anti-bacterial agents against intracellular pathogens : the specific targeting of virulence factors essential only inside the host cell. Our group has validated this approach for factors belonging to two distinct metabolic pathways : the biosynthesis of branched amino acids and of histidine. Inhibitors specific of two target enzymes block intramacrophagic replication of Brucella without affecting growth in rich medium (Boigegrain et al., Antimicrob. Agents Chemother. 2005 ; Joseph et al., Antimicrob. Agents Chemother. 2007). An ongoing interdisciplinary collaboration aims at the optimization of the inhibitor-target interaction and at the improvement of the membrane-crossing of the inhibitors into the cytosol of intracellular bacteria. Their effectiveness will have to be confirmed in the murine model of infection. The final aim of our research work will be a better understanding of the bacterial factors and mechanisms responsible of the chronic phase of Brucella infection. The results obtained in vitro will have to be validated in a murine model of chronic infection. These data may then allow the identification of novel therapeutic targets and to envisage in the long-term curative treatments of the persistent forms of brucellosis. These treatments may be potentially applicable to various chronic infectious diseases caused by intracellular bacteria, such as tuberculosis.
Scientific collaborations :
Jean-Yves Winum : Institut des Biomolécules Max Mousseron (IBMM), Montpellier, France
Maria Pilar Jimenez de Bagues : CITA, Zaragoza, Spain
Holger Scholz and Sascha Al Dahouk : Institute for Microbiology of the Army,
Munich ; RWTH University Aachen ; Germany
Garry Adams : Texas A&M University, College Station, USA
Jean-Jacques Letesson : FUNDP, Namur, Belgium
Claudiu Supuran : Université of Florence, Italy
--------------------------------------------------------
[fr]6. Stephan KOHLER - Pathogénie bactérienne et stratégies anti-infectieuses[en]6. Stephan KÖHLER - Microbiology of chronic bacterial infections and anti-infectious strategies - Brucellosis is the first bacterial zoonosis in the world, leading to chronic forms. The group is interested in the molecular mechanisms of virulence allowing Brucella to adapt to its intracellular niche inside the macrophage. The events linked to the setup of the chronic phase of infection are analyzed under (...)
