Antibacterial Activity of Kaolin–Silver Nanomaterials: Alternative Approach to the Use of Antibiotics in Animal Production

Abstract

According to the search for alternatives to replace antibiotics in animal production suggested in the antimicrobial resistance action plans around the world, the objective of this work was to evaluate the bactericidal effect of kaolin–silver nanomaterial for its possible inclusion as an additive in animal feed. The antibacterial activity of the C3 (kaolin–silver nanomaterial) product was tested against a wide spectrum of Gram-negative and Gram-positive bacteria (including multidrug resistant strains) by performing antibiograms, minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC), as well as growth inhibition curves against seven strains causing infections in animals. The C3 product generated inhibition halos in all the tested strains, and a higher activity against Gram-negative bacteria was found, with MBC values ranged from 7.8 µg/mL (P. aeruginosa) to 15.6 µg/mL (E. coli and Salmonella). In contrast, it was necessary to increase the concentration to 31.3 µg/mL or 250 µg/mL to eliminate 99.9% of the initial population of S. aureus ATCC 6538 and E. faecium ATCC 19434, respectively. Conversely, the inhibition growth curves showed a faster bactericidal activity against Gram-negative bacteria (between 2 and 4 h), while it took at least 24 h to observe a reduction in cell viability of S. aureus ATCC 6538. In short, this study shows that the kaolin–silver nanomaterials developed in the framework of the INTERREG POCTEFA EFA183/16/OUTBIOTICS project exhibit antibacterial activity against a wide spectrum of bacteria. However, additional studies on animal safety and environmental impact are necessary to evaluate the effectiveness of the proposed alternative in the context of One Health.

In Vitro Genotoxicity Evaluation of an Antiseptic Formulation Containing Kaolin and Silver Nanoparticles

“…It should be noted that the material was not completely removed after washing in the MLA and MN tests, it was present in all the following incubation steps, which makes the negative results even more significant. Furthermore, it is important to highlight that the silver-kaolin formulation demonstrated its in vitro antimicrobial activity at concentrations much lower than the ones tested in our studies, showing minimum inhibitory concentrations of 3.9–15.6 µg/mL and minimum bactericidal concentrations of 7.8–250 µg/mL, against several bacterial strains [ 25 ].…”

“…Based on the known bactericidal effect of silver, a new material was developed to be used as a feed additive, which was composed of kaolin as support for AgNPs, (Feed additive for animals: Spanish National patent N° 200701496 and Nanosystems comprising silver and antibiotics and their use for the treatment of bacterial infections: Patent in international extension China, Japan, USA, EPO, Brazil, Colombia and Mexico, N° PCT/EP2018/059006). This silver-kaolin formulation exhibited activity against a wide spectrum of Gram-negative and Gram-positive bacteria, including multidrug-resistant strains [ 25 ]. The use of the silver-kaolin formulation as alternative to antibiotics in livestock farms would contribute to a decrease in antimicrobial resistance problem caused by antibiotics overuse in animals.…”

Genotoxicity and Toxicity Assessment of a Formulation Containing Silver Nanoparticles and Kaolin: An In Vivo Integrative Approach

“…A new material composed by a metallic silver-based clay with bactericidal activity was developed and patented to be used as a feed additive [ 30 ]. Perez-Etayo and colleagues demonstrated its in vitro activity against both Gram-positive and Gram-negative bacteria, including resistant and multi-resistant ones to different antibiotic groups, being more effective against Gram-negative bacteria [ 31 ]. However, when novel materials are introduced into food sector, it is essential to understand any impact they can cause on animal or human health.…”

Biosafety evaluation of an antiseptic formulation containing silver nanoparticles

“…Also, the in vitro antibacterial activity of the silver-kaolin formulation developed in OUTBIOTICS was confirmed by Perez-Etayo and colleagues (Pérez-Etayo et al, 2021). The formulation exerted antimicrobial activity against a wide selection of gram-positive and gram-negative bacteria, including resistant and multi-resistant ones to different antibiotic groups, being more effective against gram-negative bacteria.…”

“…A formulation based on AgNPs embedded in a kaolin matrix was developed to be used as a feed additive and contribute to decrease the AMR problem. The antimicrobial activity of AgNPs has been widely demonstrated and the silver-kaolin formulation developed showed antimicrobial activity against a wide spectrum of gram-negative and gram-positive bacteria, including multidrug resistant strains (Pérez-Etayo et al 2021).…”