Antibacterial activity of Na-clinoptilolite against Helicobacter pylori: in-vitro tests, synergistic effect with amoxicillin and stability of the antibiotic formulated with the zeolite

Helicobacter pylori is a bacterium whose pathogenic strains cause severe gastroduodenal diseases. Ammonium plays a crucial role in the survival of H. pylori, and potentiates the effect of a toxin produced by the bacterium. This research has evaluated the possibility to exploit, against H. pylori growth, the selectivity of clinoptilolite towards ammonium. A specifically-prepared material containing 90% Na-clinoptilolite and H. pylori reference strain ATCC® 43504™ have been used to perform in-vitro tests. The Viable Colony Count test has evidenced, compared to the zeolite-free control, a decrease in bacterial growth from 13 to 87% for Na-clinoptilolite concentrations from 0.5 to 8 mg/mL. H. pylori growth has been inhibited in media containing 30 mg/mL of Na-clinoptilolite, whereas the same concentration of NH4-clinoptilolite, prepared through exchange from the Na-form, has allowed bacteria proliferation. The disc diffusion test revealed the existence of a synergy between amoxicillin trihydrate and Na-clinoptilolite, as the diameter of inhibition halo caused by the antibiotic has increased by 24% in growth media containing 0.125 mg/mL of Na-clinoptilolite, and by at least 70% for a zeolite concentration of 0.250 mg/mL. Conversely, NH4-clinoptilolite has not affected inhibition halo of amoxicillin. The results lead to correlate the antibacterial activity of Na-clinoptilolite with its ability to remove ammonium by cation exchange. Na-clinoptilolite does not affect the solid state stability of amoxicillin trihydrate, as determined by XRD and HPLC analyses performed on a physical mixture stored for 18 months at 20 °C and relative humidity of 20, 50, and 80%.