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


CONCLUSIONS
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.
Garzoni
Christian
C
Service of Infectious Diseases, University Hospital of Geneva, Department of Internal Medicine, Geneva 14, Switzerland. Christian.Garzoni@insel.ch <Christian.Garzoni@insel.ch+>
Francois
Patrice
P
Huyghe
Antoine
A
Couzinet
Sabine
S
Tapparel
Caroline
C
Charbonnier
Yvan
Y
Renzoni
Adriana
A
Lucchini
Sacha
S
Lew
Daniel P
DP
Vaudaux
Pierre
P
Kelley
William L
WL
Schrenzel
Jacques
J
D004847:Epithelial Cells / Q000378:metabolism*; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial; D016680:Genome, Bacterial / Q000235:genetics*; D006801:Humans; D020411:Oligonucleotide Array Sequence Analysis; D016133:Polymerase Chain Reaction; D013211:Staphylococcus aureus / Q000235:genetics* / Q000502:physiology