Background: It has been a very common practice to use probiotics or
their metabolites as alternative antimicrobial strategies for the
treatment and prevention of infections as rampant and indiscriminate
use of antibiotics causes the development of antibiotic-resistant
pathogens. The objective of this study was to select a potential
antimicrobial probiotic strain of Escherichia coli from the human
gastrointestinal tract and investigate the production of
diketopiperazines that contribute to the antimicrobial activity.
Results: E. coli GutM4was isolated from the feces of a healthy adult.
E. coli GutM4 showed significant antagonistic activity against 10
indicator pathogens, and this activity was no less than that of the
reference strain E. coli Nissle 1917 against eight of the indicator
pathogens. Moreover, E. coli GutM4 produced antagonistic substances
containing trypsin-targeted peptide bonds because the inhibitory
effects of E. coli GutM4 supernatant significantly decreased upon
treatment with trypsin. Consistent with the antagonistic activity and
peptide compounds of E. coli GutM4, 14 2,5-diketopiperazines were
isolated from the fermented broth of E. coli GutM4, including 12
cyclo(Pro-Phe), 3 cyclo(Pro-Tyr), and 5 cyclo(4-hydroxyl-Pro-Leu),
which are reported to have antipathogenic activity. Conclusion: E. coli
GutM4 produces 2,5-diketopiperazines that are partly involved in
antagonistic action against human pathogens in vitro