Abstract
Staphylococcus aureus can produce a multilayered biofilm embedded in extracellular polymeric matrix. This biofilm is difficult to remove, insensitive to antibiotics, easy to develop drug-resistant strains and causes enormous problems to environments and health. Phage lysin which commonly consists of a catalytic domain (CD) and a cell-wall binding domain (CBD) is a powerful weapon against bacterial biofilm. However, the real-time interaction between lysin and S. aureus biofilm is still not fully understood. In this study, we monitored the interactions of three lysins (ClyF, ClyC, PlySs2) against culture-on-chip S. aureus biofilm, in real-time, based on surface plasmon resonance (SPR). A typical SPR response curve showed that the lysins bound to the biofilm rapidly and the biofilm destruction started at a longer time. By using 1:1 binding model analysis, affinity constants (KD) for ClyF, ClyC, and PlySs2 were found to be 3.18 ± 0.127 μM, 1.12 ± 0.026 μM, and 15.5 ± 0.514 μM, respectively. The fact that ClyF and PlySs2 shared the same CBD but showed different affinity to S. aureus biofilm suggested that, not only CBD, but also CD affects the binding activity of the entire lysin. The SPR platform can be applied to improve our understanding on the complex interactions between lysins and bacterial biofilm including association (adsorption) and disassociation (destruction).
Highlights
Compared to microbiological laboratory conditions where Staphylococcus aureus often grows planktonically in nutrient-rich conditions, S. aureus found in the environment almost always forms sessile microbial communities called biofilms on both biotic and abiotic surfaces (Periasamy et al, 2012; Moormeier and Bayles, 2017)
Three important steps should be considered during preparation: (1) The chips must be cleaned with ammonia/hydrogen peroxide firstly; (2) High concentrations of S. aureus need to be used to form stable biofilms; and (3) Blocking with BSA is a necessary step to saturate non-specific protein absorption sites on the chip
Repeated testing was done on S. aureus biofilms only and the results were highly reproducible as shown in Supplementary Figure 1B
Summary
Compared to microbiological laboratory conditions where Staphylococcus aureus often grows planktonically in nutrient-rich conditions, S. aureus found in the environment almost always forms sessile microbial communities called biofilms on both biotic and abiotic surfaces (Periasamy et al, 2012; Moormeier and Bayles, 2017). Real-Time Biofilm-Lysin Interactions combat S. aureus biofilms owing to their strong lytic activity, high specificity, and rare chance of resistance development (Fischetti, 2008; Szweda et al, 2012; Cha et al, 2019). These specialized lysins usually have a modular structure containing two domains separated by a flexible linker region: one or more N-terminal catalytic domains (CD) for catalyzing peptidoglycan degradation and one C-terminal cell-wall binding domain (CBD) for recognizing and binding to specific cell wall ligands (Oliveira et al, 2013). Despite the successful engineering of chimeric lysis, questions still remain such as how the lysins interact with the biofilms and if different CDs and CBDs could affect the ability of lysins to remove biofilms
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