The biofilm exopolysaccharide polysaccharide intercellular adhesin--a molecular and biochemical approach

Oxytropis glabra DC. Inhibits Biofilm Formation of Staphylococcus epidermidis by Down-Regulating ica Operon Expression

Staphylococcus epidermidis is one of the main causes of medical device-related infections and bovine mastitis owing to its biofilm-forming abilities. Oxytropis glabra DC. is one of the most widespread Fabaceae species and used as a Chinese herbal formulation in Western China. Our research investigated the effects of O. glabra on the biofilm formation of S. epidermidis and the possible inhibiting mechanism. The biofilm-forming reference strain, S. epidermidis SE-1 (ATCC 35,984), was employed as a model and semi-quantitative biofilm assay was performed to evaluate the antibiofilm activity of O. glabra. The exopolysaccharides (EPS) production and expression of ica operon were studied to explore the possible antibiofilm mechanism using thin-layer chromatography and quantitative real-time PCR assay, respectively. The results obtained indicated that O. glabra decoction at 7.5 mg mL-1 significantly inhibited biofilm formation by about 95% without affecting cell growth of S. epidermidis. Two hydrolysis productions of EPS were significantly decreased by 64% and 54% with the addition of 7.5 mg mL-1O. glabra and the expression of icaR was significantly up-regulated 2.2-times, whereas icaB was significantly down-regulated more than 50% by 7.5 mg mL-1O. glabra. These findings suggest a potential application for O. glabra as a promising candidate for the exploration of new drugs against S. epidermidis biofilm-associated infections.

Transcriptional Regulation of icaADBC by both IcaR and TcaR in Staphylococcus epidermidis

S. epidermidis is a primary cause of biofilm-mediated infections in humans due to adherence to foreign bodies. A major staphylococcal biofilm accumulation molecule is polysaccharide intracellular adhesin (PIA), which is synthesized by enzymes encoded by the icaADBC operon. Expression of PIA is highly variable among clinical isolates, suggesting that PIA expression levels are selected in certain niches of the host. However, the mechanisms that govern enhanced icaADBC transcription and PIA synthesis in these isolates are not known. We hypothesized that enhanced PIA synthesis in these isolates was due to function of IcaR and/or TcaR. Thus, two S. epidermidis isolates (1457 and CSF41498) with different icaADBC transcription and PIA expression levels were studied. Constitutive expression of both icaR and tcaR demonstrated that both repressors are functional and can completely repress icaADBC transcription in both 1457 and CSF41498. However, it was found that IcaR was the primary repressor for CSF41498 and TcaR was the primary repressor for 1457. Further analysis demonstrated that icaR transcription was repressed in 1457 in comparison to CSF41498, suggesting that TcaR functions as a repressor only in the absence of IcaR. Indeed, DNase I footprinting suggests IcaR and TcaR may bind to the same site within the icaR-icaA intergenic region. Lastly, we found mutants expressing variable amounts of PIA could rapidly be selected from both 1457 and CSF41498. Collectively, we propose that strains producing enhanced PIA synthesis are selected within certain niches of the host through several genetic mechanisms that function to repress icaR transcription, thus increasing PIA synthesis.IMPORTANCE Staphylococcus epidermidis is a commensal bacterium that resides on our skin. As a commensal, it protects humans from bacterial pathogens through a variety of mechanisms. However, it is also a significant cause of biofilm infections due to its ability to bind to plastic. Polysaccharide intercellular adhesin is a significant component of biofilm, and we propose that the expression of this polysaccharide is beneficial in certain host niches, such as providing extra strength when the bacterium is colonizing the lumen of a catheter, and detrimental in others, such as colonization of the skin surface. We show here that fine-tuning of icaADBC transcription, and thus PIA synthesis, is mediated via two transcriptional repressors, IcaR and TcaR.

Molar mass, entanglement, and associations of the biofilm polysaccharide of Staphylococcus epidermidis

Biofilms are microbial communities that are characterized by the presence of a viscoelastic extracellular polymeric substance (EPS). Studies have shown that polysaccharides, along with proteins and DNA, are a major constituent of the EPS and play a dominant role in mediating its microstructure and rheological properties. Here, we investigate the possibility of entanglements and associative complexes in solutions of extracellular polysaccharide intercellular adhesin (PIA) extracted from Staphylococcus epidermidis biofilms. We report that the weight average molar mass and radius of gyration of PIA isolates are 2.01×10(5)±1200 g/mol and 29.2±1.2 nm, respectively. The coil overlap concentration, c*, was thus determined to be (32±4)×10(-4) g/mL. Measurements of the in situ concentration of PIA (cPIA,biofilm) was found to be (10±2)×10(-4) g/mL.Thus, cPIA,biofilm Collapse

Key Words

• staphylococcus epidermidis
• biofilm
• entangled polymers
• polysaccharide-protein complex
• extracellular polysaccharides
• static light scattering

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MESH Headings

• Animals
• Bacterial Adhesion
• Biofilms/growth & development
• Carbohydrate Conformation
• Cattle
• Elasticity
• Hydrogen Bonding
• Hydrogen-Ion Concentration
• Polysaccharides, Bacterial/chemistry
• Polysaccharides, Bacterial/isolation & purification
• Protein Binding
• Serum Albumin, Bovine/chemistry
• Staphylococcus epidermidis/chemistry
• Static Electricity
• Viscosity

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Grants

• R01 GM069438 NIGMS NIH HHS
• R01 GM081702 NIGMS NIH HHS
• GM-069438 NIGMS NIH HHS

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Affiliation(s)

Mahesh Ganesan Department of Chemical Engineering, University of Michigan, Ann Arbor, MI 48105
Elizabeth J. Stewart Department of Chemical Engineering, University of Michigan, Ann Arbor, MI 48105
Jacob Szafranski Department of Emergency Medicine, University of Michigan, Ann Arbor, MI 48105
Ashley Satorius Department of Emergency Medicine, University of Michigan, Ann Arbor, MI 48105
John G. Younger Department of Emergency Medicine, University of Michigan, Ann Arbor, MI 48105
Michael J. Solomon Department of Chemical Engineering, University of Michigan, Ann Arbor, MI 48105

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Collaborators Collapse

Molecular basis of Staphylococcus epidermidis infections

Staphylococcus epidermidis is the most important member of the coagulase-negative staphylococci and one of the most abundant colonizers of human skin. While for a long time regarded as innocuous, it has been identified as the most frequent cause of device-related infections occurring in the hospital setting and is therefore now recognized as an important opportunistic pathogen. S. epidermidis produces a series of molecules that provide protection from host defenses. Specifically, many proteins and exopolymers, such as the exopolysaccharide PIA, contribute to biofilm formation and inhibit phagocytosis and the activity of human antimicrobial peptides. Furthermore, recent research has identified a family of pro-inflammatory peptides in S. epidermidis, the phenol-soluble modulins (PSMs), which have multiple functions in immune evasion and biofilm development, and may be cytolytic. However, in accordance with the relatively benign relationship that S. epidermidis has with its host, production of aggressive members of the PSM family is kept at a low level. Interestingly, in contrast to S. aureus with its large arsenal of toxins developed for causing infection in the human host, most if not all "virulence factors" of S. epidermidis appear to have original functions in the commensal lifestyle of this bacterium.

Biofilm Extracellular-DNA in 55 Staphylococcus Epidermidis Clinical Isolates from Implant Infections

Biofilm formation is broadly recognized as an important virulence factor in many bacterial species implicated in implant-related opportunistic infections. In spite of a long history of research and many investigative efforts aimed at elucidating their chemical composition, structure, and function, the nature of bacterial biofilms still remains only partly revealed. Over the years, different extracellular polymeric substances (EPS) have been described that contribute functionally and structurally to the organization of biofilms. Recently extracellular DNA (eDNA) has emerged as a quantitatively conspicuous and potentially relevant structural component of microbial biofilms of many microbial species, Staphylococcus aureus and S. epidermidis among them. The present study aims at comparatively investigating the amount of eDNA present in the biofilm of 55 clinical isolates of S. epidermidis from postsurgical and biomaterial-related orthopedic infections. Quantification of eDNA was performed by a non-destructive method directly on bacterial biofilms formed under static conditions on the plastic surface of 96-well plates.

Modulation of eDNA release and degradation affects Staphylococcus aureus biofilm maturation

Recent studies have demonstrated a role for Staphylococcus aureus cidA-mediated cell lysis and genomic DNA release in biofilm adherence. The current study extends these findings by examining both temporal and additional genetic factors involved in the control of genomic DNA release and degradation during biofilm maturation. Cell lysis and DNA release were found to be critical for biofilm attachment during the initial stages of development and the released DNA (eDNA) remained an important matrix component during biofilm maturation. This study also revealed that an lrgAB mutant exhibits increased biofilm adherence and matrix-associated eDNA consistent with its proposed role as an inhibitor of cidA-mediated lysis. In flow-cell assays, both cid and lrg mutations had dramatic effects on biofilm maturation and tower formation. Finally, staphylococcal thermonuclease was shown to be involved in biofilm development as a nuc mutant formed a thicker biofilm containing increased levels of matrix-associated eDNA. Together, these findings suggest a model in which the opposing activities of the cid and lrg gene products control cell lysis and genomic DNA release during biofilm development, while staphylococcal thermonuclease functions to degrade the eDNA, possibly as a means to promote biofilm dispersal.

Loss of a biofilm-inhibiting glycosyl hydrolase during the emergence of Yersinia pestis

Yersinia pestis, the bacterial agent of plague, forms a biofilm in the foregut of its flea vector to produce a transmissible infection. The closely related Yersinia pseudotuberculosis, from which Y. pestis recently evolved, can colonize the flea midgut but does not form a biofilm in the foregut. Y. pestis biofilm in the flea and in vitro is dependent on an extracellular matrix synthesized by products of the hms genes; identical genes are present in Y. pseudotuberculosis. The Yersinia Hms proteins contain functional domains present in Escherichia coli and Staphylococcus proteins known to synthesize a poly-beta-1,6-N-acetyl-D-glucosamine biofilm matrix. In this study, we show that the extracellular matrices (ECM) of Y. pestis and staphylococcal biofilms are antigenically related, indicating a similar biochemical structure. We also characterized a glycosyl hydrolase (NghA) of Y. pseudotuberculosis that cleaved beta-linked N-acetylglucosamine residues and reduced biofilm formation by staphylococci and Y. pestis in vitro. The Y. pestis nghA ortholog is a pseudogene, and overexpression of functional nghA reduced ECM surface accumulation and inhibited the ability of Y. pestis to produce biofilm in the flea foregut. Mutational loss of this glycosidase activity in Y. pestis may have contributed to the recent evolution of flea-borne transmission.