Exploring Biosurfactants as Antimicrobial Approaches

Abstract

Antibacterial resistance is one of the most important global threats to human health. Several studies have been performed to overcome this problem and infection-preventive approaches appear as promising solutions. Novel antimicrobial preventive molecules are needed and microbial biosurfactants have been explored in that scope. Considering their structure, these biomolecules can be divided into different classes, glycolipids and lipopeptides being the most studied. Besides their antimicrobial activity, biosurfactants have the advantage of being biocompatible, biodegradable, and non-toxic, which favor their application in several areas, including the health sector. Often, the most difficult infections to fight are associated with biofilm formation, particularly in medical devices. Strategies to overcome micro-organism attachment are thus emergent, and it is possible to take advantage of the antimicrobial/antibiofilm properties of biosurfactants to produce surfaces that are more resistant to the deposition/attachment of bacteria. Approaches such as the covalent bond of biosurfactants to the medical device surface leading to repulsive physical-chemical interactions or contact killing can be selected. Simpler strategies such as the absorption of biosurfactants on surfaces are also possible, eliminating micro-organisms in the vicinity. This review will focus on the physical and chemical characteristics of biosurfactants, their antimicrobial activity, antimicrobial/antibiofilm approaches, and finally on their structure-activity relationship.

Keywords: antifouling; antimicrobial; antimicrobial release; biosurfactants; contact killing; structure–activity relationship.

Figure 1

Major advantages and drawbacks of current antimicrobial therapy and alternative strategies to overcome the shortage of new antibiotics and antimicrobial resistance.

Figure 2

Classification of microbial biosurfactants according to their chemical structure.

Figure 3

Mechanism of action of antimicrobial biosurfactants towards bacteria. Microbial biosurfactants (in purple) binding to the membrane surface (in grey) will lead to structural alterations with consequent rupture and cell lyses.

Figure 4

Representative scheme of release-based coatings. Antimicrobial compounds (presented in purple) will be released from biomaterial and promote micro-organism’s (presented in pink) membrane disruption and their death in surrounding environment and further prevent its attachment to biomaterial surface.

Figure 5

Reaction scheme of silanization: hydrolysis, hydrogen bonding, condensation.

Figure 6

Reaction scheme—oxidation, silanization, peptide bond.

Figure 7

Functionalization of gold surfaces with acidic sophorolipids (A-SLs).

Figure 8

Representative scheme of bacteria adhesion when adding biosurfactants to surfaces.