Paul M Tulkens
Université catholique de Louvain, Belgium
Paul M Tulkens has completed his MD from the Université Catholique de Louvain and he has also completed his PhD. He did his Postdoctoral studies at the Rockefeller University, New York. He has created the unit of cellular and molecular pharmacology and has also launched the activities of clinical pharmacy at the Université Catholique de Louvain. He has published more than 280 papers in reputed journals and has been serving as an Editorial Board Member of several journals dealing with antibiotics.
Production of catalase; an enzyme degrading oxygenated water (H2O2), is considered an important mechanism of protection of Staphylococcus aureus against killing by phagocytes, which partly relies on H2O2 production. We observed, however, that a catalase negative clinical isolate (UCN-61) was more resistant to H2O2 mediated killing in broth, produced less reactive oxidant species (ROS) and multiplied more rapidly in human monocytes than the reference catalase positive strain ATCC25923. By complementation UCN-31 with katA (the gene encoding catalase), we restored its susceptibility to H2O2 mediated killing, ROS production and growth impairment in monocytes. Similar results were obtained when comparing an engineered catalase (-) mutant (NR47908; prepared in the environment of the clinical strain USA300) to its katA-complemented counterpart. Addition of N-acetyl-cysteine (a hydroxyl-radicals scavenger) reduced the killing activity of H2O2 towards all catalase positive strains tested but not towards the catalase negative UCN61 and NR47908 strains, while increasing their thriving abilities after phagocytosis by THP-1 monocytes. Contrary to the current dogma, expression of catalase by S. aureus may, therefore, exert more deleterious rather than a protective effect to the bacterium. In S. aureus, catalase may actually function more as oxidase than as H2O2 degrading enzyme but ROS produced as intermediates during H2O2 degradation could be also involved.