Research article

A global view of Staphylococcus aureus whole genome expression upon internalization in human epithelial cells

Christian Garzoni¹ , Patrice Francois¹ , Antoine Huyghe¹ , Sabine Couzinet¹ , Caroline Tapparel¹ , Yvan Charbonnier¹ , Adriana Renzoni¹ , Sacha Lucchini² , Daniel P Lew¹ , Pierre Vaudaux¹ , William L Kelley¹ and Jacques Schrenzel¹

¹  Service of Infectious Diseases, University Hospital of Geneva, Department of Internal Medicine, 24 rue Micheli-du-Crest, CH-1211 Geneva 14, Switzerland

²  Molecular Microbiology Group, Institute of Food Research, Norwich Research Park, Colney, Norwich, NR4 7UA, UK

author email corresponding author email

BMC Genomics 2007, 8:171doi:10.1186/1471-2164-8-171

Published:	14 June 2007

Abstract

Background

Staphylococcus aureus, a leading cause of chronic or acute infections, is traditionally considered an extracellular pathogen despite repeated reports of S. aureus internalization by a variety of non-myeloid cells in vitro. This property potentially contributes to bacterial persistence, protection from antibiotics and evasion of immune defenses. Mechanisms contributing to internalization have been partly elucidated, but bacterial processes triggered intracellularly are largely unknown.

Results

We have developed an in vitro model using human lung epithelial cells that shows intracellular bacterial persistence for up to 2 weeks. Using an original approach we successfully collected and amplified low amounts of bacterial RNA recovered from infected eukaryotic cells. Transcriptomic analysis using an oligoarray covering the whole S. aureus genome was performed at two post-internalization times and compared to gene expression of non-internalized bacteria. No signs of cellular death were observed after prolonged internalization of Staphylococcus aureus 6850 in epithelial cells. Following internalization, extensive alterations of bacterial gene expression were observed. Whereas major metabolic pathways including cell division, nutrient transport and regulatory processes were drastically down-regulated, numerous genes involved in iron scavenging and virulence were up-regulated. This initial adaptation was followed by a transcriptional increase in several metabolic functions. However, expression of several toxin genes known to affect host cell integrity appeared strictly limited.

Conclusion

These molecular insights correlated with phenotypic observations and demonstrated that S. aureus modulates gene expression at early times post infection to promote survival. Staphylococcus aureus appears adapted to intracellular survival in non-phagocytic cells.