Synergism and Efficacy of Some Naturally Occurring D-amino Acids Against Clinically Relevant Bacterial and Fungal Species

Amino acids are predominantly synthesized and used in their l-enantiomeric form in all three kingdoms of life. however, bacteria produce diverse d-amino acids that are involved in the synthesis and cross-linking of peptidoglycan. several studies reported possible antimicrobial activities of selected d-amino acids against escherichia coli. the present study was undertaken to investigate the antibacterial and antifungal susceptibility patterns and growth inhibitory effects of certain d-amino acids, including d-alanine, d-lysine, d-serine, and d-proline. our findings indicate that dlysine is the most potent antibacterial and antifungal, among the examined d-amino acids, followed by d-alanine, whereas d-serine and d-proline had insignificant antimicrobial activities. gram positive bacteria were more susceptible to the antibacterial effects of d-amino acids than gram negative bacteria. growth kinetic studies revealed that d-lysine and d-alanine resulted in extended lag phases, suggesting that the d-amino acids successfully influenced the microorganisms’ ability to use nutrients efficiently and disrupted their normal biological functions. additionally, synergism was evident between d-alanine and d-lysine when combined with either ampicillin or amphotericin b. these results suggest a new avenue for d-amino acids’ potential as naturally occurring antimicrobial reagents for the treatment and prevention of microbial growth in food and agriculture applications