Antimicrobial agents based on metal-ion zeolite materials: a multivariate approach to microbial growth inhibition

Bacteria are susceptible to zeolites doped with metal ions. Although the complete mode of action remains unclear, it is widely accepted that metal ions kill bacteria by inducing the production of reactive oxygen species (ROS), which are detrimental to microbial life processes. In this study, two zeolite structures, MFI and LTA, were selected as hosts for the preparation of various metal-ion zeolite materials, which were then tested for their antimicrobial activity against eight different bacterial strains—Escherichia coli, Enterococcus faecalis, Klebsiella pneumoniae, Staphylococcus saprophyticus, Proteus mirabilis, Pseudomonas aeruginosa, methicillin-sensitive Staphylococcus aureus (MSSA) and methicillin-resistant Staphylococcus aureus (MRSA)—and five yeasts—Saccharomyces cerevisiae, Candida albicans, Candida tropicalis, Candida glabrata and Candida parapsilosis. Minimum inhibitory concentrations (MICs) and antimicrobial efficacies (%) were determined for each material–microbe pair. In addition to comparing eukaryotic and prokaryotic models, bacterial susceptibility was assessed across differences in cell wall structure (Gram-positive vs. Gram-negative), growth phase (exponential vs. stationary), and strain type (clinical isolate vs. type strain). Principal component analysis (PCA) and hierarchical clustering were used to identify patterns across MIC and antimicrobial efficacy data of the antimicrobial performance of metal-ion zeolite materials. Furthermore, ANOVA-simultaneous component analysis (ASCA) was applied on a balanced a posteriori designed dataset to assess the contribution of experimental factors to the observed variance. To demonstrate a direct application, selected samples were preliminary tested as coatings for fruit packaging to evaluate their potential for prolonging shelf life. These findings highlight the potential of metal-ion exchanged zeolites as antimicrobial agents for healthcare and food packaging applications.