Chelating agents exert distinct effects on biofilm formation in Staphylococcus aureus depending on strain background: role for clumping factor B

Abstract

Staphylococcus aureus is a leading cause of catheter infections, and biofilm formation plays a key role in the pathogenesis. Metal ion chelators inhibit bacterial biofilm formation and viability, making them attractive candidates as components in catheter lock solutions. The goal of this study was to characterize further the effect of chelators on biofilm formation. The effect of the calcium chelators ethylene glycol tetraacetic acid (EGTA) and trisodium citrate (TSC) on biofilm formation by 30 S. aureus strains was tested. The response to subinhibitory doses of EGTA and TSC varied dramatically depending on strain variation. In some strains, the chelators prevented biofilm formation, in others they had no effect, and they actually enhanced biofilm formation in others. The molecular basis for this phenotypic variability was investigated using two related strains: Newman, in which biofilm formation was inhibited by chelators, and 10833, which formed strong biofilms in the presence of chelators. It was found that deletion of the gene encoding the surface adhesin clumping factor B (clfB) completely eliminated chelator-induced biofilm formation in strain 10833. The role of ClfB in biofilm formation activity in chelators was confirmed in additional strains. It was concluded that biofilm-forming ability varies strikingly depending on strain background, and that ClfB is involved in biofilm formation in the presence EGTA and citrate. These results suggest that subinhibitory doses of chelating agents in catheter lock solutions may actually augment biofilm formation in certain strains of S. aureus, and emphasize the importance of using these agents appropriately so that inhibitory doses are achieved consistently.

Staphylococcus aureus clumping factor B mediates biofilm formation in the absence of calcium

“…Out of these, we found only two, TCH60 and ST38, with mutations leading to premature stop codons. Because we found in our earlier study (Abraham et al, 2012) that nearly 30 % of S. aureus isolates form strong biofilms in EGTA, and we confirmed in a number of these strains that biofilm formation in EGTA was ClfB-dependent, we hypothesize that additional genetic differences must lead to the observed phenotype in other strains. For example, clfB transcript levels could be higher in some strains or aur transcript levels could be lower.…”

“…We found previously (Abraham et al, 2012) that a subset of S. aureus strains produce strong biofilms in the presence of the chelating agents EGTA and trisodium citrate. We also found that if we deleted clfB in these strains, the ability to produce a biofilm under chelating conditions was nearly completely abolished.…”

“…We found in a separate study (Abraham et al, 2012), that subinhibitory concentrations of the chelating agents trisodium citrate and EGTA effectively reduce biofilm formation in a subset of S. aureus isolates, whereas in some strains, they do not exert an appreciable effect, and in other strains they actually significantly augment biofilm formation. The finding that chelating agents can augment biofilm formation in some strains may have important clinical implications as citrate is used in catheter lock solutions such as Citra-Lock and DuraLock-C (although the FDA does not approve citrate for this use in the USA (O'Grady et al, 2011).…”

Innovative Strategies for Combating Biofilm-Based Infections

“…Some metal ions play an important role in biofi lm formation, stimulating cell-cell adhesion and aggregation (Abraham et al 2012 ), and the effect of metal ion chelation upon biofi lm formation has been investigated as a strategy to combat biofi lms. Ethylenediaminetetraacetic acid (EDTA) was shown to disperse P. aeruginosa biofi lms and result in 1,000-fold enhanced killing by gentamicin (Banin et al 2006 ), while a combination of EDTA and minocycline effectively reduced in vitro and ex vivo staphylococcal catheter colonization (Raad et al 2003 ).…”

Two repetitive, biofilm-forming proteins from Staphylococci: from disorder to extension

“…However, more recently, bacterial surface proteins involved in cell-cell interactions have also been identified [6]. S. aureus and S. epidermidis surface proteins that have been implicated in biofilm formation include SasC [7], SesC and Embp [8], fibronectin-binding proteins (FnBPs) [9][10][11], the fibrinogen-binding protein ClfB [12], SasG and Aap [13,14] and the recently discovered Sbp which influences both polysaccharide and protein-dependent biofilm formation in S. epidermidis [15]. The balance between PNAG/PIAdependent and protein-dependent biofilm formation affects biofilm morphology and this balance can differ between S. aureus and S. epidermidis; clinical and non-clinical isolates and under different environmental conditions [9,[16][17][18].…”