Are Clay Minerals in Jordanian Soils Antibacterial?

Clay separates have been recently evaluated for their antibacterial potential. The current research is conducted to investigate theantibacterial effects of clay fractions from Jordanian soils and their relation to the physical and chemical properties of the soils.Thirty three soil samples were collected from different sites in the country with a high clay content (mainly from northern andmiddle governorates). The physical and chemical properties of bulk soil and clay fractions were characterized. Thereafter, theclay fractions were screened for their antibacterial propertiesin vitroagainst common bacterial pathogens and clinical isolatesknown for their multidrug resistance.Seven clay fractions showed antibacterial properties against one or more of the tested pathogens in liquid culture. The X-raydiffraction (XRD) and X-ray Florescence (XRF) results of the antibacterial clay were correlated with the bacterial growthinhibition to understand the antibacterial mechanisms.Correlation analyses using Pearson’s product moments and backward elimination stepwise regressions indicated that the testedmicrobial strains are being significantly affected by different physical and chemical properties of the soil (e.g. EC, CEC, Availablewater), soil solution ionic concentrations (e.g. HCO^-and SO^2-, Na^+, and Ca^2+), clay fraction composition (Clay-Fe-oxide, Clay CaCO_3), and clay type (smectites, quartz, and englishite). On the other hand, FeO, AlO, and MgO clay compositions were found to be the most effective factors governing the antimicrobial activity. Thus, each microbial strain has a specific inhibitorcontrol that interacts with its antimicrobial mechanism. As a conclusion, this study indicates the bactericidal effect of some claymineral fractions from Jordanian soils, which still need to be clinically tested before use in medical applications.