2.10 Antimicrobial peptides
AMPs, also known as host defense peptides, are short, positively charged
proteins found in many organisms, including humans. They have the
ability to directly eliminate harmful microbes or enhance the body’s
immune response. With the growing issue of antibiotic resistance, AMPs
are being recognized as potential therapeutic solutions. They provide
quick and targeted action against bacteria that are resistant to
traditional antibiotics and have a low risk of developing resistance,
positioning them as excellent options for antibacterial
treatments.25 Bacteria often produce AMPs to fight off
rival bacteria within their environment.26Gram-positive and Gram-negative bacteria have membranes with negatively
charged lipids that attract the positively charged AMPs. In
Gram-negative bacteria, AMPs first need to breach the outer membrane,
which is strengthened by cations like calcium and magnesium attached to
lipopolysaccharides. AMPs likely use a method where they displace these
cations, creating temporary openings in the outer membrane for entry.25,27 Antimicrobial peptides (AMPs) fight bacteria
mainly by interacting with their membranes in different ways. Some
peptides insert into the membrane to create pores, while others coat the
membrane surface and disrupt it like a detergent when they reach a high
concentration. Additionally, some peptides cause the membrane to bend
around a central opening. AMPs can also block the creation of cell walls
and inhibit the production of proteins or genetic material. Among the
most studied AMPs are insect-derived peptides, particularly cecropins,
which effectively target bacteria like E. coli by damaging their
membranes.28 AMPs causes ion leakage and
depolarization that lead to membrane dysfunction and rapid cell
lysis.29 Although bacteria are less likely to resist
AMPs due to their multiple targets, recent studies show that resistance
can develop under selective pressure, and AMPs also face challenges due
to low stability and high production costs.25,30 In
ovo treatment with D-CATH-2 reduced APEC mortality and bacterial load in
chickens. Combining surfactin with amoxicillin enhanced its
effectiveness, lowering mortality and APEC levels while boosting
cytokine genes. Peptides like A3 and cecropin A-D-Asn also decreasedE. coli in the chicken gut, suggesting antimicrobial peptides as
alternatives or supplements to antibiotics in poultry.2,31