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

Christian Garzoni,Sabine Couzinet,Antoine Huyghe,William L Kelley,Daniel P Lew,Yvan Charbonnier,Pierre Vaudaux,Adriana Renzoni,Caroline Tapparel,Jacques Schrenzel,Patrice Francois,Sacha Lucchini

doi:10.1186/1471-2164-8-171

Christian Garzoni, Sabine Couzinet + Show 10 more

Open Access

https://doi.org/10.1186/1471-2164-8-171

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Abstract

BackgroundStaphylococcus 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.ResultsWe 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.ConclusionThese 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.

Highlights

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
Infection model and bacterial RNA isolation We developed a model system that displayed protective survival of S. aureus 6850 within human lung epithelial cells A549
We examined the intracellular survival of strain 6850 as a function of time using the lysostaphin/gentamicin protection

Summary

Introduction

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. S. aureus is responsible for chronic diseases such as osteomyelitis [9], rhinosinusitis [10], or otitis [11] These infections are difficult to eradicate and often relapse even after prolonged and adapted antibiotic therapy [12,13], suggesting that S. aureus has developed specific strategies for intracellular persistence. Anti-infective agents commonly used for the treatment of S. aureus infections could enhance selection of invasive intracellular strains [14]

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