Abstract
Numerous studies have investigated the antibacterial effect of both silver ions and silver nanomaterials on a large diversity of environmentally and clinically relevant bacteria. However, contradictory results are reported in which inhibition concentrations were varying by a 10-fold. This study investigated whether this variance in results could be attributed to the difference in experimental conditions, especially the microbial growth medium. B. subtilis was exposed to 500 µg L−1 Ag+ in liquid growth media with different concentrations of some commonly used media components: tryptone, yeast extract, Cl−, and S2−. The toxic effect was investigated by means of three complementary analysis techniques: (i) analyzing the growth curves obtained by optical density measurements, (ii) using flow cytometry, and (iii) by transmission electron microscopy. The silver ion toxicity towards B. subtilis decreased as more tryptone, yeast extract, or S2− was present. This study demonstrates that the medium composition, rarely acknowledged as an important experimental factor in bacterial toxicity studies, has a profound impact on the observed silver toxicity towards B. subtilis.
Highlights
Silver and its salts have been used for centuries for its effective antibacterial, antifungal, and antiviral properties in preserving water or food and preventing infections of wounds
The results show that the undefined complex components tryptone (C) and yeast extract (D) can totally diminish the antibacterial effect of 500 μg L−1 Ag+ at a concentration of 1 g L−1 tryptone or yeast extract
In order to increase our understanding in this respect, we investigated whether growth media components can affect the toxic effect of Ag+ perceived by bacteria, here the gram-positive model organism B. subtilis
Summary
Silver and its salts have been used for centuries for its effective antibacterial, antifungal, and antiviral properties in preserving water or food and preventing infections of wounds. In order to predict the possible ecological and human toxicity of silver, as well as to verify the antimicrobial effect of new products and applications, a large number of scientific papers describe toxicity tests for AgNPs, Ag+, and colloidal silver towards a wide range of pure or mixed cultures of bacteria in both growth media or biological matrices. Mainly attributed to Ag+ 18, we investigated the influence of some commonly used growth media components on the antimicrobial effect of Ag+ on B. subtilis in this paper
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