Abstract
BackgroundMany chronic diseases, such as non-healing wounds are characterized by prolonged inflammation and respond poorly to conventional treatment. Bacterial biofilms are a major impediment to wound healing. Persistent infection of the skin allows the formation of complex bacterial communities termed biofilm. Bacteria living in biofilms are phenotypically distinct from their planktonic counterparts and are orders of magnitude more resistant to antibiotics, host immune response, and environmental stress. Staphylococcus aureus is prevalent in cutaneous infections such as chronic wounds and is an important human pathogen.ResultsThe impact of S. aureus soluble products in biofilm-conditioned medium (BCM) or in planktonic-conditioned medium (PCM) on human keratinocytes was investigated. Proteomic analysis of BCM and PCM revealed differential protein compositions with PCM containing several enzymes involved in glycolysis. Global gene expression of keratinocytes exposed to biofilm and planktonic S. aureus was analyzed after four hours of exposure. Gene ontology terms associated with responses to bacteria, inflammation, apoptosis, chemotaxis, and signal transduction were enriched in BCM treated keratinocytes. Several transcripts encoding cytokines were also upregulated by BCM after four hours. ELISA analysis of cytokines confirmed microarray results at four hours and revealed that after 24 hours of exposure, S. aureus biofilm induced sustained low level cytokine production compared to near exponential increases of cytokines in planktonic treated keratinocytes. The reduction in cytokines produced by keratinocytes exposed to biofilm was accompanied by suppressed phosphorylation of MAPKs. Chemical inhibition of MAPKs did not drastically reduce cytokine production in BCM-treated keratinocytes suggesting that the majority of cytokine production is mediated through MAPK-independent mechanisms.ConclusionsCollectively the results indicate that S. aureus biofilms induce a distinct inflammatory response compared to their planktonic counterparts. The differential gene expression and production of inflammatory cytokines by biofilm and planktonic cultures in keratinocytes could have implications for the formation and persistence of chronic wounds. The formation of a biofilm should be considered in any study investigating host response to bacteria.
Highlights
Many chronic diseases, such as non-healing wounds are characterized by prolonged inflammation and respond poorly to conventional treatment
We investigated the transcriptional response of Human keratinocytes (HKs) exposed to S. aureus biofilm conditioned medium (BCM) and planktonic conditioned medium (PCM) to reveal genes associated with pathogenesis
planktonicconditioned medium (PCM) was found to contain several enzymes involved in glycolysis while biofilm-conditioned medium (BCM) contained proteins relating to translation in addition to proteins which were not identified by a Mascot search
Summary
Many chronic diseases, such as non-healing wounds are characterized by prolonged inflammation and respond poorly to conventional treatment. Bacterial biofilms are a major impediment to wound healing. In many environments bacteria exist as a complex, multispecies surface-associated community termed biofilm. Bacteria within these communities secrete an extracellular polymer matrix, form complex structures, and are Bacterial biofilms are a major barrier to healing in chronic wounds. Chronic-wound biofilms are not cleared by the host’s immune system and are resistant to traditional treatment strategies such as antibiotics [6]. Chronic wounds display abnormal progression through these phases including prolonged inflammation and failure to re-epithelialize. A recent study showed that biofilms were prevalent in chronic wounds and rare in acute wounds [8], but the role biofilms play in preventing wound healing and mechanisms involved have yet to be determined
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