Bacteria Can Hide Out In Cells For Weeks
By Nicole Kenny, Virox Technologies Inc.

Another interesting study was released recently that revealed a fascinating survival strategy used by Staphylococcus aureus. The paper, “A global view of Staphylococcus aureus whole genome expression upon internalization in human epithelial cells,” was published earlier this year in BMC Genomics and profiled in ScienceDaily. It explained that Staph. Bacteria may evade the immune system’s defences and dodge antibiotics by climbing into our cells and then lying low to avoid detection. The research shows how S. aureus makes itself at home in human lung cells for up to two weeks.

A team of 12 researchers from University Hospital of Geneva, Switzerland and the Institute of Food Research, Norwich, UK, set out to uncover what S. aureus did inside human lung epithelial cells using an in vitro model. They found that shortly after S. aureus entered the lung cells, the bacteria’s gene expression profile dramatically changed: gene expression for bacterial metabolic functions and transport shut down, putting the bacteria in a dormant state.

Simultaneously, production of toxins potentially lethal for the epithelial cells becomes strictly controlled to limit cellular damage. Mechanisms that helped the bacteria to survive and/or multiply, including metabolic and energy production functions, then resumed. Although most of the bacteria had died by about four days as a result of antibiotic treatment, the team still found viable bacteria in their model system two weeks after infection.

The findings may help in understanding relapsing infections (even years after the first episode was apparently cured), and in designing a new antibacterial drugs. S. aureus has not traditionally been considered an intracellular pathogen, but the molecular details that govern its extended persistence remain largely unknown.