Combined effect of eucalyptus microcorys aqueous extract and light on pathogenic escherichia coli survival in aquatic microcosm

Abstract

Microcosm experiments were carried out to investigate the effect of Eucalyptus microcorys aqueous plant extract on pathogenic Escherichia coli survival in water. The results clearly showed that the combined effect of light and extract concentration impacted significantly survival of the bacteria. The dark inhibition coefficient (KD) was 0.102 h-1, 0.116 h-1, 0.111 h-1, 0.123 h-1, 0.136 h-1 and 0.146 h-1 with 0.05%, 0.1%, 0.5%, 1%, 1.5% and 2% of extract concentration respectively. In the light conditions, we noted a relative increase of light inhibition coefficient (KL). The Self-Organizing Map according to incubation duration of cells in the extract solution permitted to group bacterial abundances in three clusters. Cluster I is the abundance of cells registered after 24 hours incubation in the plant extract solution. Cluster II is made up of all cells abundances registered after 9 and 12 hours incubation and Cluster III is constituted by cells abundances obtained after 3 and 6 hours incubation. Globally, for extract concentration 1, 1.5 and 2%, a calculation using Chick-Watson model resulted to a value of log(N/No) =-0.1Ct which is very close to chlorine disinfectant Chick-Watson model log(N/No) =-0.16 Ct. These results can improve in the new alternative method of treatment water by plant extracts.