Naturally occurring layered-mineral magnesium as a bactericidal against Escherichia coli

• Published in: Applied clay science 2017-12, Vol.149, p.87-96
• Main Authors: Zarate-Reyes, Luis, Lopez-Pacheco, Cynthia, Nieto-Camacho, Antonio, Apán, María Teresa Ramírez, Palacios, Eduardo, Kaufhold, Stephan, Ufer, Kristian, Garcia-Zepeda, Eduardo, Cervini-Silva, Javiera
• Format: Article
• Language: English
• ISSN: 0169-1317; 1872-9053
• DOI: 10.1016/j.clay.2017.07.035

Escherichia coli (E. coli) is a versatile organism that can colonize and adapt in the environment, and an example of antibiotic resistant bacteria, persistent throughout the world because they have evolved to express various defense mechanisms to cope with antibiotics and the immune system, therein the need to find good strategies for their treatment, such as the application of industrial minerals. Located in the outer section of the external membrane of E. coli, gram-negative bacteria, is lipid A, the lipid component of an endotoxin that consists of lipopolysaccharides, which is responsible for its toxicity of the bacteria. Arguably, the antibacterial activity of naturally occurring minerals is mediated by surface interactions with lipid A. Here, we study the antibacterial activity of layered mineral Mg against E. coli using in vitro and in vivo tests, and report on: (i) in-vitro E. coli (ATCC 25922) growth behavior (bacteriostatic or bactericidal activity); and (ii) in-vitro RAW264.7 cells growth. Furthermore, the oxidative stress, oxidative degradation of lipids in cell membrane resulting in cell damage via lipid peroxidation (LP), was quantified in vivo using the Thiobarbituric Acid Reactive Substances (TBARS) assay. Finally, since inflammation is the first reaction of an organism to defend itself from outside attack by microorganisms or toxic compounds, clinical tests for inflammation using two independent methods, namely to quantify the inhibition of edema [12-O-tetradecanoylphorbol-13-acetate (TPA) method] and the migration of neutrophils [Myeloperoxidate (MPO) method] were in turn assessed. Growth curves (log phase) for E. coli showed that adding brucite or talc in concentrations as low as 20μgmL−1 cause death. Absorbance values at λ=600nm were found to be significantly lower in magnitude relative to positive controls, with no evidence for the presence of Colony Forming Units (CFUs) in agar plates at 24 or 48h. Critical to E. coli growth, Mg acts as a cofactor of alkaline-phosphatase metaloenzyme(s); however, as a layered mineral, Mg exerts irreversible negative effects. Meanwhile, results showed a poor bactericidal activity of sepiolite, owing a higher microporosity and number of surface reaction sites, which were then attributed to gelification at the surface vicinity, provoked by dislocations at inversion sites of the tetrahedral sheet. Taken together these results showed that the bactericidal activity of layered mineral Mg was restricted by phy