Full Length Research Paper

Survival of free-living and plankton-associated Escherichia coli in the final effluents of a waste water treatment facility in a peri-urban community of the Eastern Cape Province of South Africa

Augustina N. Osode and Anthony I. Okoh*

Department of Biochemistry and Microbiology, Applied and Environmental Microbiology Research Group (AEMREG), University of Fort Hare, Alice X1314, South Africa.

*Corresponding author. E-mail: aokoh@ufh.ac.za.

Accepted 9 June, 2010

   Abstract

Escherichia coli remains a major threat in many places around the globe as a major causative agent of diarrhea and its reservoir in the estuarine environment may play an important role in the survival and transport of pathogenic strains. The final effluents of a peri-urban waste water treatment facility were assessed for surviving E. coli community as free-living or plankton-associated cells in relation to some physicochemical parameter for a year period. The free-living E. coli population densities varied from 0 to 3.13 × 101 cfu/ml, while the plankton-associated E. coli densities vary with plankton sizes as follows: 180 µm (0 - 4.30 × 10¹ cfu/ml), 60 µm (0 - 4.20 × 10¹ cfu/ml), 20 µm (0 - 5.00 × 101 cfu/ml). The seasonal variations in the E. coli densities among the plankton size categories were significant (P < 0.05). Correlation analysis suggested that the counts of E. coli correlated negatively with salinity (P < 0.001) and positively with temperature, pH, turbidity and dissolved oxygen (P < 0.001) in the final effluent. Target genes that encode pathogenicity for E. coli were successfully amplified by PCR. The study suggested that final effluents are a significant sources of pathogenic E. coli in the receiving watershed.

Key words: Escherichia coli, free-living, plankton-associated, wastewater final effluent.