Interleukin-1beta-induced growth enhancement of Staphylococcus aureus occurs in biofilm but not planktonic cultures.
Staphylococcus aureus causes recalcitrant infections and forms resistant biofilms. Mechanisms of biofilm resistance to host defenses may include changes in gene expression that confer responsiveness to chemical mediators. In earlier studies fresh clinical isolates responded to inflammatory cytokines, but responsiveness was lost after multiple in vitro passages [Meduri et al. Cytokines IL-1beta, IL-6, and TNF-alpha enhance the In vitro growth of bacteria. Am J Respir Crit Care Med 1999;160:961-7]. Since biofilms more closely resemble in vivo growth and are implicated in recalcitrant infections, we hypothesized that biofilms, but not planktonic cells, would respond to cytokines. Biofilms were induced by ethanol in S. aureus ATCC 12600. Biofilms treated with 2 ng/mL interleukin-1beta (IL-1beta) for 6 h contained 2.5-fold more cells than untreated biofilms, but no growth-enhancement occurred in planktonic cultures. As determined by flow cytometry, IL-beta bound to 63.1% of biofilm cells, but only 11.2% of planktonic cells. Our results provide evidence of a differential response of biofilm and planktonic bacteria to chemical mediators, and suggest that biofilm bacteria may evade host defenses by growing more rapidly in response to the inflammatory mediators released by activated host defense cells.
McLaughlin
Renee A
RA
Department of Biology, Calvin College, 1726 Knollcrest Circle SE, Grand Rapids, MI 49546-4403, USA.
Hoogewerf
Arlene J
AJ
D001431:Bacteriological Techniques; D018441:Biofilms / Q000187:drug effects* / Q000254:growth & development*; D054407:Chemokine CCL4; D004305:Dose-Response Relationship, Drug; D005434:Flow Cytometry / Q000379:methods; D007375:Interleukin-1 / Q000378:metabolism / Q000494:pharmacology*; D015850:Interleukin-6 / Q000494:pharmacology; D019402:Macrophage Inflammatory Proteins / Q000494:pharmacology; D011135:Polysaccharides, Bacterial / Q000096:biosynthesis / Q000235:genetics; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology*; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D015854:Up-Regulation
D054407:Chemokine CCL4; D007375:Interleukin-1; D015850:Interleukin-6; D019402:Macrophage Inflammatory Proteins; D011135:Polysaccharides, Bacterial; D014409:Tumor Necrosis Factor-alpha; C113579:polysaccharide intercellular adhesin