Use of non-bound proteinogenic amino acids to modulate the growth of pathogenic bacteria from broiler chickens

Pathogenic bacteria can inhabit the chicken intestinal tract and potentially cause disease and mortality in chickens. Proteinogenic amino acids are major nutrients available in the intestine that have diverse growth-modulating effects on bacteria. However, limited knowledge exists about the direct association between amino acids and the growth of bacteria in the microbiome of the chicken's intestinal tract. The present study evaluated the growth-modulating effects of the 20 proteinogenic amino acids on chicken pathogens. Seven bacterial species were tested, including avian pathogenic Escherichia coli (APEC), Salmonella enterica., Staphylococcus aureus, Clostridium perfringens, Enterococcus cecorum, Enterococcus faecalis, and Enterococcus faecium. All bacteria were tested in minimal nutrient medium (MNM) in an in vitro model, with or without the addition of each amino acid. Bacterial growth was measured by absorbance (OD₆₀₀) and visualised as growth curves. l-cysteine significantly (p ≤ 0.05) inhibited the growth of APEC, extended the lag phase and increased the maximum density of C. perfringens, Salmonella enterica. and S. aureus. In contrast, l-glutamine and l-glutamic acid significantly shortened the lag phase and increased both the growth rate and maximum density of C. perfringens, Glycine and l-serine significantly (p ≤ 0.05) increased the maximum density of S. aureus. The effect of amino acids was insignificant (p ≥ 0.05) on the total growth of Enterococcus spp. These findings suggested that l-cysteine has inhibiting effects on APEC, C. perfringens, S. enterica and S. aureus. l-glutamine and l-glutamic acid promoted the growth of C. perfringens, while glycine and l-serine promoted the growth of S. aureus.