PRELIMINARY ECOLOGICAL INVESTIGATIONS OF E. COLI INTERACTIONS WITH AQUEOUS SUSPENSIONS OF NA-MONTMORILLONITE, ILLITE, AND PALYGORSKITE

Antibacterial properties of clay minerals have been periodically reported in the literature, however these reports are often preliminary in nature and do not address many mineralogical variables nor do they address the specific mechanisms causing supposed cell death. We investigated phyllosilicates having systematic structural variation of 2:1 layers: an illite, a Na-montmorillonite and a palygorskite-rich clay. An illite used in our experiments is from the Diecke K-bentonite, Mauzy VA and is similar to the illite reported by Williams et al. (2004) as having antibacterial properties on Escherichia coli. The average measured pH of suspensions of illite was 6.92 and the percent solids was 2.39 %. The average measured pH of suspensions of Na-montmorillonite was 9.20 and the average percent solids of the suspension was 2.90 wt%. For palygorskite-rich clay average measured pH of suspensions was 7.20 and the average percent solids was 0.782%. For the experiments a lab strain of E. coli was used. Three replicates of each clay or control media were produced. Each tube had 9.0 ml of clay suspension (or distilled water, or control). Once the E. coli was inoculated into each tube, the abundance of viable E. coli was determined at time zero, using a dilution, spread plate count approach with Nutrient agar. Viable cells were enumerated from exposure times ranging from t=0 hours to t= 24 hours. Our results indicate that no aqueous suspension of any of the minerals investigated killed the bacteria. Furthermore there was no qualitative indication that these minerals had an inhibitory effect.