Intracellular pharmacodynamics of antibiotics against small-colony variants of staphylococcus aureus in in vitro models of professional phagocytic cells
(2012)
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- Authors
- Supervisors
- Van Bambeke, Françoise
- Abstract
- (en) Intracellular survival of Staphylococcus aureus is associated with persistent infections and antibiotic failure, especially due to the emergence of Small-Colony Variants (SCVs). The aim of this thesis was to study the intracellular fate of menadione- and hemin-dependent SCVs of the COL methicillin-resistant S. aureus (MRSA) strain and the antibiotic pharmacodynamic profile against these particular forms. This work was oriented in three main directions. Firstly, we evaluated the intracellular activity of antibiotics in a model of THP-1 monocytes expressing poor intrinsic defenses. We demonstrated that the menadione-dependent mutant systematically showed lower amplitude of the concentration-effect response, with markedly reduced minimal efficacy (due to slower growth) but no change in maximal efficacy. The data therefore show that the maximal efficacies of antibiotics are similar against normal-phenotype and menadione- and hemin-dependent strains despite their different intracellular fates, with oritavancin (a new lipoglycopeptide in development), and to some extent moxifloxacin (a fluoroquinolone), being the most effective as previously observed also for a thymidine-dependent SCV in the same model. Secondly, we have examined how activation of monocytes into macrophages modulates antibiotic activity against our strains, as reactive oxidant species (ROS) may be critical in antibiotic-dependent bacterial killing. It appeared that differentiation induced by PMA treatment may increase the intracellular relative potency of antibiotic according to the dependence of their activity on ROS. Conversely, agents for whom cell activation has minimal effect, like oritavancin, may be advantageous when host defense mechanisms are weakened. Finally, we focused on the MRSA character of our strains. Previously, it was indeed shown in our laboratory that phagocytized MRSA were susceptible to bêta-lactams because the acid pH of phagolysosomes induces a conformational change of PBP2a allowing its acylation by these antibiotics. Our study has examined whether this mechanism also applies for SCVs. Using N-acetylcystein or hydrogen peroxide as scavenger or booster of ROS, we showed that cooperation between acidic pH and oxidant species confers high potency to bêta-lactam against intracellular forms of menadione-dependent SCVs of MRSA. Thus, our work has permitted to fill an important lack of data with respect to the pharmacodynamics of antibiotics against intracellular SCVs and to make some unexpected observations. In contrast to what would have been expected, SCVs indeed appeared more susceptible to antibiotics in the intracellular environment due to their hyper-susceptibility to burst oxidative.
- Affiliations
Citations
Garcia, L. (2012). Intracellular pharmacodynamics of antibiotics against small-colony variants of staphylococcus aureus in in vitro models of professional phagocytic cells. https://hdl.handle.net/2078.5/74528