Sodium Salicylate Influences the Pseudomonas aeruginosa Biofilm Structure and Susceptibility Towards Silver.

Erik Gerner,Margarita Trobos,Peter Thomsen,Maria Werthén,Sofia Almqvist

doi:10.3390/ijms22031060

Abstract

Hard-to-heal wounds are typically infected with biofilm-producing microorganisms, such as Pseudomonas aeruginosa, which strongly contribute to delayed healing. Due to the global challenge of antimicrobial resistance, alternative treatment strategies are needed. Here, we investigated whether inhibition of quorum sensing (QS) by sodium salicylate in different P. aeruginosa strains (QS-competent, QS-mutant, and chronic wound strains) influences biofilm formation and tolerance to silver. Biofilm formation was evaluated in simulated serum-containing wound fluid in the presence or absence of sodium salicylate (NaSa). Biofilms were established using a 3D collagen-based biofilm model, collagen coated glass, and the Calgary biofilm device. Furthermore, the susceptibility of 48-h-old biofilms formed by laboratory and clinical strains in the presence or absence of NaSa towards silver was evaluated by assessing cell viability. Biofilms formed in the presence of NaSa were more susceptible to silver and contained reduced levels of virulence factors associated with biofilm development than those formed in the absence of NaSa. Biofilm aggregates formed by the wild-type but not the QS mutant strain, were smaller and less heterogenous in size when grown in cultures with NaSa compared to control. These data suggest that NaSa, via a reduction of cell aggregation in biofilms, allows the antiseptic to become more readily available to cells.

Highlights

Increased Silver Susceptibility of Biofilms Formed by Pseudomonas aeruginosa in the Presence of NaSa
At 100 ppm silver, the 5 mM NaSa treatment resulted in a significant 2.8 log10 reduction in viable cell counts, while 10 mM NaSa resulted in no viable cells compared to control biofilms grown without NaSa (Figure 1b)
These results revealed that biofilms grown in the presence of NaSa were more susceptible to silver than control biofilms, this effect was observed to a lesser extent for the Quorum sensing (QS)-mutant

Summary

Introduction

1.5% of the population in the Western world will suffer from hard-toheal wounds [1], and the presence of biofilms in these wounds is among the most important contributors to delayed healing [2]. Aggregated bacteria in biofilms are substantially more tolerant to antimicrobial agents and the host immune system than their planktonic counterparts due to protective biofilm matrix components, such as proteins, polysaccharides, and extracellular DNA (eDNA) [3]. A recent systematic review and meta-analysis revealed that a majority of chronic wounds (78%) contain biofilms [4], which are believed to contribute to delayed wound healing and should, be targeted when treating chronic wounds [2]. Alongside debridement and cleaning of the wound, the topical or systemic administration of antimicrobials can be used to combat biofilm-associated infections [2]

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