Bacteriocins as a new generation of antimicrobials: toxicity aspects and regulations

Abstract

In recent decades, bacteriocins have received substantial attention as antimicrobial compounds. Although bacteriocins have been predominantly exploited as food preservatives, they are now receiving increased attention as potential clinical antimicrobials and as possible immune-modulating agents. Infections caused by antibiotic-resistant bacteria have been declared as a global threat to public health. Bacteriocins represent a potential solution to this worldwide threat due to their broad- or narrow-spectrum activity against antibiotic-resistant bacteria. Notably, despite their role in food safety as natural alternatives to chemical preservatives, nisin remains the only bacteriocin legally approved by regulatory agencies as a food preservative. Moreover, insufficient data on the safety and toxicity of bacteriocins represent a barrier against the more widespread use of bacteriocins by the food and medical industry. Here, we focus on the most recent trends relating to the application of bacteriocins, their toxicity and impacts.

Keywords: antimicrobials; bacteriocins; gastrointestinal bioavailability; regulations; safety evaluation; toxicity.

Figure 1.

Physiological conditions that may influence the stability and biological activity of bacteriocins during the gastrointestinal transit. Figure created in biorender, https://biorender.com/.

Figure 2.

Bacteriocin interplays in the gastrointestinal tract. 1. Stability in gastrointestinal condition including enzymes, pH changes, commensal bacteria; 2. Possible pathways for bacteriocin absorption by epithelial cells; 3. Bacteriocin interaction with immune system.

Figure 3.

In vitro toxicity assays. Three different assays that have been mostly employed for toxicity evaluation of bacteriocins based on various cell functions: 1. Neutral red assay (measures cell viability upon lysosome function), 2. MTT assay (measures cell viability upon mitochondria activity), and 3. LDH release assay (membrane Integrity).

Figure 4.

4A. Main targets for bacteriocins in Gram-positive and Gram-negative bacteria. A. Perturbations of the membrane bilayer by pore formation and efflux of ions and metabolites; B. Perturbation of cell wall synthesis; C. Membrane depolarization; D. Perturbation of septum formation; E. Disruption of replication and transcription; F. Inhibition of ribosomal function and perturbation of protein synthesis; G. Blocking of chaperon functions necessary for proper folding of proteins. Bacteriocins ( ) 4B. Mechanism of bacterial resistance to antibiotics and bacteriocins. A. Mutation of a receptor; B and C. Modifications of the membrane composition; D. Septum formation E. Expression of efflux pumps; F. Expression of immunity genes; G. Degradation or inactivation of chaperones. Bacteriocins ( ), Antibiotics ( ) Figures created in biorender https://biorender.com/. (There are symbols for bacteriocins as red cross in bracets and antibiotics as green cross in brackets which can't be added here please consider those.

Figure 5.

Guideline for evaluation and approval of new bacteriocins for food applications.

Figure 6.

Guideline for evaluation and approval of new bacteriocins for human and veterinary applications.

Figure 7.

Guideline for safety evaluation of bacteriocins intended for food, human, and animal uses.