The present invention provides a heat-stable and protease-resistant antibacterial activity in excretory-secretory products (ESP) of Trichuris suis. The antibacterial activity is not more than 10,000 MW; is resistant to boiling, trypsin, and pronase E; has a bactericidal mode of action; and is effective against Gram positive and Gram negative bacteria, including Escherichia coli, Campylobacter jejuni, Campylobacter coli, and Staphylococcus aureus. The antibacterial activity is useful in applications for killing or inhibiting the growth of microorganisms, in particular bacteria.