Antibacterial activity of Zn-loaded Cuban zeolite against Helicobacter pylori in comparison to its Na-loaded and unmodified counterparts

Helicobacter pylori can be found in the stomach of about half of the humans, and a large population can be associated with serious diseases. To survive in the stomach H. pylori increases the pH locally by producing ammonia which binds to H(+) becoming ammonium. This work investigated the effects on the in-vitro growth of H. pylori of a natural cation-exchanger mainly composed (≈70%) of clinoptilolite and mordenite. The zeolitized material from Cuba was evaluated in its original form (M), as well as in its Na- (M-Na) and Zn-exchanged (M-Zn) counterparts. In the preliminary agar cup diffusion test, H. pylori revealed susceptibility only to M-Zn, with a direct relationship between concentration and width of inhibition halo. Further experiments evidenced that bacterium replication increases when ammonium is supplied to the growth medium and decreases when zeolites subtract NH(4)(+) via ion exchange. Due to the multi-cationic population of its zeolites M was not effective enough in removing ammonium and, in the Minimum Inhibitory Concentration (MIC) test, allowed bacterial growth even at a concentration of 50 mg/mL. Inhibition was achieved with M-Na because it contained sodium zeolites capable of maximizing NH(4)(+) subtraction, although the MIC was high (30 mg/mL). M-Zn evidenced a more effective inhibitory capacity, with a MIC of 4 mg/mL. Zinc has antimicrobial properties and H. pylori growth was affected by Zn(2+) released from clinoptilolite and mordenite. These zeolites, being more selective towards NH(4)(+) than Zn(2+), can also subtract ammonium to the bacterium, thus enhancing the efficacy of M-Zn. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s10653-020-00781-2) contains supplementary material, which is available to authorized users.