Synergistic and Antagonistic Effects of Phenylalanine and Various Antibiotics on the Growth of Pathogenic Bacteria

Abstract

Broad-spectrum antibiotics have been widely used in the treatment of many systemic and local infections in humans and animals. Herein, we aimed to determine the synergistic and antagonistic effects of phenylalanine with antibiotics cefoxitin, amoxicillin, vancomycin, lincomycin, and bacitracin against 14 pathogenic bacteria. The effect of antibiotics, either alone or in combination with this biomolecular liquid, was tested using the disk diffusion method against different bacteria. The addition of phenylalanine to antibiotic disks directly affected their antimicrobial activity. All the antibiotics used did not show any antimicrobial activity against Staphylococcus haemolyticus when used alone. However, in combination with phenylalanine, each antibiotic inhibited the growth of S. haemolyticus. The use of this biomolecular liquid together with amoxicillin and vancomycin also increased the antimicrobial activity against Enterococcus durans. The use of phenylalanine in combination with antibiotics also resulted in antagonistic effects on some pathogens. Further, the effects of antibiotics in combination with phenylalanine on different bacterial pathogens were investigated in vitro. Results provide valuable information to further our understanding of the molecular mechanism of action of antibiotics and to improve their efficacy against bacterial pathogens.