Bacterial persistent or recurrent infections are associated with two specific lifestyles, namely intracellular survival and biofilms. We are studying antibiotic activity against these two forms of infections in relationship with antibiotic pharmacokinetics (factors determining antibiotic access to the target).
- Cellular pharmacokinetics
We study the cellular accumulation (including the mechanisms of entry) and the subcellular localization of novel molecules in preclinical and clinical development, as a basis for further studies examining their intracellular activities in specific compartments. We try to decipher the mechanisms for their penetration and distribution within the cells. Over the last years, we have focused our interest on new antibiotic classes, like lipoglycopeptides, ketolides and new oxazolidinones now present on the market. We are now examining innovative antibiotic classes acting on still unexploited targets in order to define their capacity to accumulate within the cells and then to define their interest for the treatment of intracellular infections.
- Cellular pharmacodynamics
In parallel, we study the activity of antibiotics against intracellular bacteria sojourning in different subcellular compartments, mainly Listeria mono-cytegenes (cytosol), Staphylococcus aureus (phago-lysosomes), and Pseudomonas aeruginosa. We developed an in vitro pharmacodynamic approach to compare the efficacy and the potency of the drugs. In brief, we showed that antibiotics are in general less effective but equipotent against intracellular than against extracellular bacteria, irrespective of their accumulation level. We also studied specific phenotypes (Small Colony Variants [SCV] of S. aureus) known for their intracellular persistence and poor susceptibility to antibiotics and examined the interest of antibiotic combinations against multiresistant strains. The data generated with these models have been incorporated to the dossier having led to the registration of the last antibiotics brought on the market.
We are now trying to identify specific genes involved in intracellular persistence. Conversely, we are also examining the role of virulence factors (mainly type three secretion systems) in cytotoxicity and are determining the molecular mechanisms thereof. Specifically, using a collection of clinical isolates from acute infections, we showed that, depending on the type of toxins produced, P. aeruginosa caused cell death by necrosis or by pyroptosis consecutive to the activation of the inflammasome cascade. On this basis, we are now studying inhibitors of virulence as adjuctive therapy to antibiotics.
- Antibiotic activity against biofilms
We developed in vitro pharmacodynamic models to evaluate the activity of antibiotics against biofilms made of S. aureus, S. pneumoniae or P. aeruginosa. We showed that antibiotic efficacy and relative potency are considerably reduced in biofilms as compared to planktonic cultures. With S. aureus, we found that biofilms made of clinical strains isolated from patients suffering from persistent infections are still more refractory to antibiotics. We could demonstrate that this was mainly due to a default of penetration of the antibiotics within these biofilms, which could attribute to the matrix composition (polysaccharide content) (Figure 5). We are now exploring innovative strategies in order to disrupt this matrix and increase antibiotic activity. With S. pneumoniae, we studied clinical isolates from patients suffering from chronic obstructive pulmonary disease. We examined wether bronchodilators taken by these patients could modify biofilm formation and response to antibiotics. We could show that anticholinergic drugs completely disrupted the matrix while beta-agonists stimulated bacterial neuraminidase, an enzyme involved in biofilm remodelling, with as consequence, an increase in antibiotic activity. These data show that bronchodilators effects could thus have favourable effects on the outcome of these patients beyond their known pharmacological activity.