TITLE:
Germicidal Action of Some Metals/Metal Ions in Combating E. coli Bacteria in Relation to Their Electro-Chemical Properties
AUTHORS:
Alakaparampil Joseph Varkey, Mgidi Donald Dlamini, Anaclet Bwampamye Mansuetus, Ababu Teklemariam Tiruneh
KEYWORDS:
Metal Inactivation; Disinfection; Heavy Metal Toxicity; Water Treatment; Rate of Inactivation; Escherichia coli
JOURNAL NAME:
Journal of Water Resource and Protection,
Vol.5 No.12,
December
9,
2013
ABSTRACT:
The germicidal properties of some metals and metal compounds were investigated in relation to their electro-chemical properties that may play a role in the inactivation of E. coli bacteria. These properties included the atomic and ionic radii, ionization energy, oxidation state, energy of formation with hydro-sulfide groups, and the redox potential of the metals. Cultures of E. coli bacteria with predetermined numbers of colony-forming units (CFU’s) were brought in contact with the metals as well as metal compounds, using Eosin methylene blue agar medium and sterilized, distilled water. The rate of inactivation was determined by counting the CFU’s at predefined intervals of time after inoculation. The experimental results showed that the rate of inactivation increases with increasing ionization energy of the metals. While the rate of inactivation increases with decreasing atomic radii for some of the transition metals, there is no apparent relationship between ionic radius and rate of inactivation for the metal compounds. In addition, non-transition group III metals such as aluminum and indium showed higher rates of inactivation that are comparable to the action of silver. This is probably due to the increase in coagulation potential and the resulting adsorption of bacteria, because a larger number of ions are able electrons carried by these atoms. In general, there is a difference between the atoms and the ions in terms of their rate of inactivation. This difference increases amongst the transition metals that have lower oxidation potential, lower ionization potential as well as larger ionic radius. The results also showed that for the metals, adsorption through coagulation is an important fact or that is responsible for inactivation of E. coli. For the metal compounds, additional mechanisms such as direct reaction through complex formation, physico-chemical distortion of the cell structure through direct entry of the ions into the cell, may contribute towards greater inactivation.