Early effects of Staphylococcus aureus biofilm secreted products on inflammatory responses of human epithelial keratinocytes

Abstract

BackgroundChronic wounds such as diabetic foot ulcers, pressure ulcers, and venous leg ulcers contribute to a considerable amount of mortality in the U.S. annually. The inability of these wounds to heal has now been associated with the presence of microbial biofilms. The aim of this study was to determine if products secreted by S. aureus biofilms play an active role in chronic wounds by promoting inflammation, which is a hallmark of chronic wounds.MethodsIn vitro experiments were conducted to examine changes in gene expression profiles and inflammatory response of human epithelial keratinocytes (HEKa) exposed to products secreted by S. aureus grown in biofilms or products secreted by S. aureus grown planktonically.ResultsAfter only two hours of exposure, gene expression microarray data showed marked differences in inflammatory, apoptotic, and nitric oxide responses between HEKa cells exposed to S. aureus biofilm conditioned media (BCM) and HEKa cells exposed to S. aureus planktonic conditioned media (PCM). As early as 4 hours post exposure, ELISA results showed significant increases in IL-6, IL-8, TNFα, and CXCL2 production by HEKa cells exposed to BCM compared to HEKa cells exposed to PCM or controls. Nitric oxide assay data also showed significant increases in nitric oxide production by HEKa cells treated with BCM compared to HEKa cells treated with PCM, or controls.ConclusionsTaken together, these results support and extend previous findings that indicate products secreted by S. aureus biofilms directly contribute to the chronic inflammation associated with chronic wounds.

Biphasic influence of Staphylococcus aureus on human epidermal tight junctions

“…We found an upregulation of proinflammatory cytokines IL‐1β, IL‐6, IL‐8, and TNF‐α upon live S. aureus treatment. An upregulation of gene expression of these cytokines in NHEKs was reported using S. aureus biofilm–secreted products, S. aureus biofilm–conditioned medium, or planktonic‐conditioned medium . An involvement of these cytokines in the S. aureus –induced increase in TER is also supported by the fact that the addition of IL‐1β and TNF‐α to infected keratinocytes here produced a short‐term TER‐increasing effect.…”

In vitro studies evaluating the effects of biofilms on wound‐healing cells: a review

“…). The reduction in primary HK viability , proliferation , and migration due to BCM and PCM was later confirmed by other investigators using different strains of S. aureus . BCM‐induced apoptosis was also demonstrated in another primary HK investigation and in the HaCaT cell line , which is an immortalized keratinocyte cell line.…”

“…Using primary HK, Tankersley et al. performed a similar investigation. They examined the production of IL‐1, IL‐6, IL‐8, TNF‐α, and CXCL‐2 after both 4 and 8 h of exposure to either S. aureus BCM or PCM.…”

Effect of UV-photofunctionalization on oral bacterial attachment and biofilm formation to titanium implant material

“…We also observed that the biomass attached to UV-treated titanium remained sparse, predominantly consisting of individual attached cells and small cell clusters compared to untreated surfaces that were mostly covered in maturing biofilms comprised of large colonies that appeared to be encased in matrix material. In addition to preventing host cell attachment to the implant by competing for space, biofilms have also been shown to elicit much stronger inflammatory response – an important reason for bone loss – compared to planktonic bacteria [57, 58]. Furthermore, bacteria contaminating titanium implants have been demonstrated to migrate into and infect surrounding tissues, while apparently not being cleared by macrophages [59].…”