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Simultaneous lack of catalase and beta-toxin in Staphylococcus aureus leads to increased intracellular survival in macrophages and epithelial cells and to attenuated virulence in murine and ovine models

Susana Martínez-Pulgarín

Departamento de Sanidad Animal, Facultad de Veterinaria, Universidad Complutense de Madrid, Avda. Puerta de Hierro s/n, 28040 Madrid, Spain

Staphylococcus aureus produces a variety of virulence factors that allow it to cause a wide range of infections in humans and animals. In the latter, S. aureus is a leading cause of intramammary infections. The contribution of catalase (KatA), an enzyme implicated in oxidative stress resistance, and beta-toxin (Hlb), a haemolysin, to the pathogenesis of S. aureus is poorly characterized. To investigate the role of these enzymes as potential virulence factors in S. aureus, we examined the intracellular survival of katA, hlb and katA hlb mutants in murine macrophages (J774A.1) and bovine mammary epithelial cells (MAC-T), and their virulence in different murine and ovine models. Catalase was not required for the survival of S. aureus within either J774A.1 or MAC-T cells. However, it was necessary for the intracellular proliferation of the bacterium after invasion of MAC-T cells. In addition, catalase was not needed for the full virulence of S. aureus in mice. Deletion of the hlb gene had no effect on the intracellular survival of S. aureus in J774A.1 cells but did cause a slight increase in survival in MAC-T cells. Furthermore, like catalase, beta-toxin was not required for complete virulence of S. aureus in murine models. Unexpectedly, the katA hlb mutant showed a notably increased persistence in both cell lines, and was significantly less virulent for mice than were the wild-type strain and single mutants. Most interestingly, it was also markedly attenuated in intramammary and subcutaneous infections in ewes and lambs.

Correspondence
Ricardo de la Fuente
rifuente{at}vet.ucm.es

Present address: Departamento de Biotecnología, Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA), Crta. de La Coruña km. 7.5, 28040 Madrid, Spain.

The University Complutense of Madrid (Spain) has filed a patent on the katA hlb strain as a vaccine against ruminant mastitis.