Retention of Escherichia coli cells through a sand column during percolation of bacteria-contaminated water with a neutral pH: The potential role of the cell growth phase and sterilized or unsterilized nature of the sand grains

Abstract

The present study aims to assess the retention of Escherichia coli cells harvested from 3 different growth phases, contained in water pH 7 percolating through sterilized and unsterilized sand grains of 3 size ranges (0.1-0.3mm, 0.3-0.5mm, and 0.5-0.8mm). Water containing E. coli (7×107 CFU/mL) was prepared in an Erlenmeyer flask with the tap connected. The bacteriological analysis of water percolated was carried on the first drops, then after 2h, 4h, 6h and 8h. Results showed that through sterilized sand columns, cells abundances in water percolated varies from 5.2×104 to 22.48×104, , from 2.43×104 to 9.88×104 and from 1×104 to 4,26×204 CFU/mL with cells harvested from the lag, and stationary phase, respectively. Through unsterilized sand columns, they varied from 2.02×104 to 9.31×104, from 0.5×104 to 12.35×104 and from 1.7×104 to 5.04×104 CFU/mL with cells from the lag, exponential and stationary phase, respectively. Overall, the cells retained percentages (CRP) seems smaller with sterilized sand compared to unsterilized sand grain when bacteria cells were harvested from lag and exponential phases. The CRP seems also varying with percolation duration considering each grain size and sand type, and when considering all 3 growth phases. The Mann-Whitney comparison test showed a significant difference (P<0.05) between sterilized and unsterilized sand in cells abundance contained in water percolated through sand size 0.1-0.3mm for each of the cells growth phase. It also shown significant difference in cells abundance contained in water percolated through sterilized sand when cells were harvested from different growth phases (P<0.05), but not through unsterilized sand columns.