Comparative Evaluation of Antibacterial Effects of Zeolite Composite Powder and Protamine Sulfate on Escherichia coli, Bacillus subtilis, and B. subtilis Endospores

Bacterial contamination in the environment poses a significant threat to human health. Herein, we investigated the antibacterial properties of zeolite composite powder containing silver, titanium and zinc ions, designed for potential use in environmental bacterial decontamination. Non-pathogenic Escherichia coli, Bacillus subtilis, B. subtilis endospores and an ampicillin-resistant fluorescent E. coli strain were employed as test organisms. Considering that combinations of antimicrobial agents can exhibit synergistic effects, zeolite composite powder was also tested in combination with the antimicrobial peptide protamine sulfate. Results showed that 500 mg of zeolite composite with a contact time of 15 minutes was required to inhibit E. coli growth, whereas B. subtilis growth was completely inhibited at a much lower dose (50 mg). Germinated B. subtilis endospores were effectively inhibited by combining 90 mg zeolite composite with 1 mg mL-1 protamine. Furthermore, zeolite composite significantly reduced the colony count of ampicillin-resistant fluorescent E. coli in liquid culture after 5 hours of treatment, achieving greater inhibition than protamine alone, which reduced colonies by 85%. When applied to alginate bead–immobilized fluorescent E. coli, zeolite also proved more effective than protamine in decreasing bacterial viability. Overall, this study highlights not only the strong antibacterial potential of zeolite composites but also underscores the importance of optimizing contact time for rapid and efficient bacterial decontamination in environmental applications.