Antibacterial activity of Na-clinoptilolite against Helicobacter pylori: in-vitro tests, synergistic effect with amoxicillin and stability of the antibiotic formulated with the zeolite
Mauro Farina, Antonio Brundu, Maria Cristina Bonferoni, Claudia Juliano, Giovanna Rassu, Elisabetta Gavini, Guido Cerri
Microporous and Mesoporous Materials, Volume 288, 1 November 2019, Article 109592
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%.