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Identification of a Staphylococcus aureus strain with increased intracellular growth and reduced intracellular susceptibility to gentamicin

Abstract number: P1060

Olivier A., Van Bambeke F., Mingeot-Leclercq M.P., Tulkens P.M.

Objectives: The persistence and recurrence of many S. aureus infections (such as endocarditis) has been ascribed to its intracellular character. Our aim was to examine the intracellular development of S. aureus strains differing by their hemolysin (hl) production as well as their intracellular response to antibiotics, using both phagocytic (THP-1) and endothelial cells (HUVEC).

Methods: Intracellular growth was measured by the change in CFU (Delta log /mg prot.) recorded 24 h after infection. Controls were maintained with gentamicin (1 x MIC) to prevent the development of extracellular bacteria. Confocal microscopy was performed with bacteria tagged with fluorescein isothiocyanate, and vital staining of lysosomes using LysoTracker® Red DND 99.

Results:S. aureus DU5942 showed a more important intracellular growth than the other strains (also observed in HUVEC). This was not due to hlg disruption, since it was also observed for the complemented strain DU5942-M1 but not for the multidisruptant strain DU5938. Dose-effects studies with gentamicin showed a similar response for all tested strains extracellularly. In contrast, DU5942 and its M1 mutant were less sensitive to gentamicin than 8325–4 intracellularly, exposure to higher extracellular concentrations being required to prevent intracellular growth. No difference was seen between strains for other antibiotics (oxacillin, vancomycin or telavancin). Confocal microscopy showed that, after 24 h of infection, all strains were confined in lysosomes in THP-1 macrophages. In endothelial cells, most bacteria colocalised with lysosomes but a small number appeared free in the cytoplasm.

Conclusion: We identified a strain with high capacity of intracellular growth in both professional phagocytes and endothelial cells. This effect seems to be related to a lower intracellular susceptibility of the strain to gentamicin but not to its hl status.

Session Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Subject:
Location: Barcelona, Spain
Presentation type:
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