The myth of antibiotic spider silk

Simon Fruergaard,Marie Braad Lund,Andreas Schramm,Thomas Vosegaard,Trine Bilde

doi:10.1016/j.isci.2021.103125

Abstract

SummarySpider silk is frequently attributed antimicrobial properties. This notion is based on studies reporting antimicrobial activity (AMA) of spider silk; however, close inspection of these studies reveals that the evidence is conflicting, and at best anecdotal. We performed a systematic study of antimicrobial properties of different silk types from seven species across the spider phylogeny. We found no evidence of AMA of silk in direct contact and disc diffusion assays against Gram-negative Escherichia coli and Pseudomonas putida, and the Gram-positive Bacillus subtilis. Furthermore, staining experiments and fluorescence microscopy showed the presence of live bacteria on silk surfaces indicating no antimicrobial effect on direct contact. A critical evaluation of the literature reveals that published tests of AMA are scarce and that all the studies claiming positive results are compromised by methodological shortcomings. Our analysis demonstrates that the common notion that spider silk is antimicrobial is not supported by empirical data.

Highlights

Spiders express extraordinary behavioral and physiological adaptations that enable them to occupy a very broad range of habitats
We found no evidence of antimicrobial activity (AMA) of silk in direct contact and disc diffusion assays against Gram-negative Escherichia coli and Pseudomonas putida, and the Gram-positive Bacillus subtilis
Spiders were kept under sterile conditions and retreat silk collected AMA was investigated by WDA and Disk diffusion assay (DDA) with native silk, water, and ethanol extracts AMA was investigated by growing bacteria in various media directly on orb webs and by cross-streaking AMA test in liquid E. coli culture

Summary

Introduction

Spiders express extraordinary behavioral and physiological adaptations that enable them to occupy a very broad range of habitats. Spider silk was attributed healing properties and records report a variety of medical applications, in particular in relation to wound healing (Heimer, 1988; Newman and Newman, 1995). In this context, silk fibers are believed to possess antimicrobial properties, and studies reporting potential antimicrobial molecules on spider silk, such as metal chelators (Hu et al, 2007) and fatty acids (Hattori et al, 1987), have substantiated this notion (Romer and Scheibel, 2008; Saravanan, 2006). Spider silks are protein-based fibers with primarily nonpolar and hydrophobic amino acids (Romer and Scheibel, 2008; Vollrath, 2000) that may be targeted as substrate for microbes, requiring antimicrobial properties as defense

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Conclusion