Amino acids are vital for bacteria to grow and express specific functions and can be sourced from the environment. The availability of amino acids from the environment may affect the activity and growth pattern of bacteria (1). The response of the bacteria to exogenous amino acids is both amino acid and species specific (2). This suggested that certain amino acids can selectively suppress the growth of opportunistic pathogens in the intestine. Although the bacterial response to amino acids varies between strains, a hypothesis stipulated is that bacteria with similar origin will have similar responses to exogenous amino acids (3). The aim of this experiment is to discover the amino acids that can suppress the growth of some intestinal opportunistic pathogen, such as pathogenic Escherichia coli and Salmonella enterica. As a result of the experiment, diets can be formulated with encapsulated amino acids to reduce the growth of these bacteria in the intestine.
In vitro experiments were performed in 96 well plates. Serval opportunistic pathogens from broiler chicken were tested for their growth performance in a minimal broth media with and without the presence of the 20 different proteogenic amino acids. Absorbance (OD600) was measured at 2-hour intervals from 0 to 14 hour of incubation followed by measurements at 24 and 48 hours. Growth curves were produced from the measurement using a 96-well plate reader. The carrying capacity (maximum population that can be reached), growth rate, and doubling time of the bacteria were calculated and compared to show the effect of the amino acids on the bacterial growth. These calculations were done in Rstudio with an R package, growthcurver. Statistical significance of the differences in growth between the absence or presence of each amino acid was evaluated using paired t-tests or Wilcoxon signed rank tests depending on the normality of the data.
Preliminary result demonstrated that cysteine and histidine could inhibit and delay the growth of E. coli, respectively. In conclusion, specific amino acids have the potential to alter the growth pattern of bacteria.
This research was supported by the AgriFutures Chicken Meat Consortium on Nutrition, Gut Health, and Environment.