Offre de stage de Master 1 (printemps 2023) ou Master 2

In vivo regulation of Staphylococcus aureus pathogenicity in different larval microenvironnements

In vivo regulation of Staphylococcus aureus pathogenicity in different larval microenvironnements

Stage : M1 ou M2

Titre du stage : In vivo regulation of Staphylococcus aureus pathogenicity in different larval microenvironnements

Encadrants : Drs Guillaume Ménard et Yoann Augagneur

Laboratoire : INSERM U1230 – BRM - Faculté des sciences Pharmaceutiques et Biologiques – 2 av du Prof Léon Bernard – 35043 Rennes

Merci de transmettre CV et lettre de motivation à : guillaume [dot] menardatchu-rennes [dot] fr et yoann [dot] augagneuratuniv-rennes1 [dot] fr


Staphylococcus aureus, a major pathogen, is responsible for a large set of infections, ranging from minor skin infections to life-threatening conditions. It is also a skin and cutaneous commensal colonizing about a third of the general population. Its adaptation to the ever-changing environmental conditions requires the coordinated expression of various factors, some of them being under the control of sRNAs. Over the last few years, we develop the use of the Galleria mellonella in vivo larvae model to investigate S. aureus adaptation, with specific focus on three different microenvironments: the haemolymph (the circulatory system), haemocytes (the neutrophil equivalent), and nodules (S. aureus abscess in mammals). To date, preliminary results showed that haemocytes could be successfully separated from haemolymph, allowing recovering extracellular and intracellular S. aureus, highlighting a low bacterial load. Nodules were highly selected by microdissection-laser, with probably a low bacterial load. To circumvent this, we initiate the use of digital droplet PCR (ddPCR), by developing and optimizing it, both in vitro and in vivo in infected conditions by targeting the three microenvironments.

In our lab, we focus in a particular aspect of S. aureus regulation, namely that mediated by sRNAs. Some of them are connected to S. aureus virulence regulation but the in vivo understanding of sRNAs remains a topic that is still relatively unexplored. RNAIII is the most studied and characterized sRNA, being a critical node in S. aureus virulence regulation, with many other regulators and virulence factors connected to this one. However, we previously demonstrated that the deletion of RNAIII does not affect virulence in G. mellonella model but observed a high mortality when RNAIII was overexpressed. These paradoxal results are not limited to the G. mellonella model but also described in other vertebrate infection models and in humans. One hypothesis is a narrow sRNA expression that are expressed or repressed by many stimuli, which may be different for a given microenvironment.

Objective: By a selected approach, we intend to better decipher the in vivo crucial effect of RNAIII and therefore S. aureus adaptation in different microenvironments by targeting a key node of regulation and the associated host response. Infections will be performing by testing three S. aureus strains: the HG003 reference strain, the mutated one, and the isogenic overexpressed RNAIII strain. Analyses of RNAIII regulon will be realized in vivo, in the three microenvironments, and at different times during the infection progress. At least, RNAIII targets such as virulence factors (spa, sbi, coa, SA1000, lytM, hla) and transcription factors (rot, mgrA) will be monitored. Others actors such as SprY and RsaA, that are sRNAs recently link to RNAIII, could be as well. Host immune humoral response will also be scrutinized such as antimicrobial peptides, opsonins, or lysozyme.

Methods: invertebrate animal models, microdissection-laser, molecular biology (RNA extraction, ddPCR, qPCR)

NB: For M1 degree, only two strains will be selected i.e. the HG003 reference strain and the isogenic overexpressed RNAIII strain. The three microenvironments will be concerned but only the host response will be studied through qPCR.