Dynamic interaction between airway epithelial cells andStaphylococcus aureus

Abstract

Staphylococcus aureus is a major cause of pulmonary infection, particularly in cystic fibrosis (CF) patients. However, few aspects of the interplay between S. aureus and host airway epithelial cells have been investigated thus far. We investigated by videomicroscopy the time- and bacterial concentration-dependent (104, 106, and 108CFU/ml) effect of S. aureus on adherence, internalization, and the associated damage of the airway epithelial cells. The balance between the secretion by S. aureus of the α-toxin virulence factor and by the airway cells of the antibacterial secretory leukoproteinase inhibitor (SLPI) was also analyzed. After 1 h of interaction, whatever the initial bacterial concentration, a low percentage of S. aureus (<8%) adhered to airway cells, and no airway epithelial cell damage was observed. In contrast, after 24 h of incubation, more bacteria adhered to airway epithelial cells, internalized bacteria were observed, and a bacterial concentration-dependent effect on airway cell damage was observed. At 24 h, most airway cells incubated with bacteria at 108CFU/ml exhibited a necrotic phenotype. The necrosis was preceded by a transient apoptotic process. In parallel, we observed a time- and bacterial concentration-dependent decrease in SLPI and increase in α-toxin expression. These results suggest that airway cells can defend against S. aureus in the early stages of infection. However, in later phases, there is a marked imbalance between the bactericidal capacity of host cells and bacterial virulence. These findings reinforce the potential importance of S. aureus in the pathogenicity of airway infections, including those observed early in CF patients.

LiveStaphylococcus aureusand bacterial soluble factors induce different transcriptional responses in human airway cells

“…However, Weinrauch et al (52) showed that low doses of ␣-toxin induce DNA fragmentation and cell death, whereas high doses result in massive necrosis without DNA fragmentation. In agreement with Da Silva et al (10), who have worked on the same MM-39 cell line, we observed a prominent necrosis phenotype of the MM-39-cells, with a transient apoptotic process 9 h after interaction (Fig. 5).…”

“…Fluorescent images were recorded every 30 min for 24 h as previously described (10). Variations of the YO-PRO-1 and of the propidium iodide fluorescence intensities were expressed as the ratio of the fluorescence intensity at a given time to the initial fluorescence intensity.…”

“…MM-39 cells were incubated with either live bacteria or bacterial supernatant (prepared as described in EXPERIMENTAL PROCE-DURES), and RNA were profiled to evaluate the respective contributions of a direct contact with live bacteria or of soluble components to the transcriptional response. After 3 h of exposure to 10 8 CFU/ml of live S. aureus (equivalent to a multiplicity of infection of 50 bacteria per cell), 15.0 Ϯ 6.5% of the total number of airway epithelial cells exhibited adherent bacteria. Internalized bacteria were detected in 3.0 Ϯ 2.3% of the cells.…”

Genetic susceptibility to S. aureus mastitis in sheep: differential expression of mammary epithelial cells in response to live bacteria or supernatant

“…Regulation of apoptosis is a very complex phenomenon, and the analysis of the MEC transcriptome in the various conditions of stimulation tested in our study confirms this complexity. Moreilhon et al (34) also reported the presence of antiapoptotic genes in airway cells stimulated by Sp, and to a lesser extent by Sa, whereas many other reports show proapoptotic mechanisms consecutive to an infection (5,30,48,52). As a result we cannot make a clear conclusion about apoptosis; a large increase in MEC apoptosis might reveal degradation of the mammary gland tissue and so an alteration of its functioning, whereas enhanced apoptosis might be also a normal phenomenon with the cell turnover.…”

Downregulation by a long-acting β2-adrenergic receptor agonist and corticosteroid of Staphylococcus aureus-induced airway epithelial inflammatory mediator production

“…S. aureus surface proteins such as adhesins and protein A are produced during exponential growth phase, whereas most exoproteins, including toxins, hemolysins, and tissue-degrading enzymes, are secreted during the stationary phase. Alpha-toxin, one of the major soluble VF of S. aureus, is able to induce transient apoptosis followed by the necrosis of human airway epithelial cells (HAEC) (9). We have also recently shown that live S. aureus and more predominantly soluble VF in contact with HAEC induce marked alterations in the transcriptional expression profile of HAEC associated with activation of the NF-B and activator protein (AP)-1 pathway, upregulation of PGE 2 and cyclooxygenase (COX)-2 expression and proinflammatory cytokine release such as IL-1␤ and IL-8 (23).…”