Cadmium tolerance and antibiotic resistance in Escherichia coli isolated from waste stabilization ponds.

The incidence pattern of cadmium tolerance and antibiotics resistance by Escherichia coli was examined periodically from the samples of water, sludge and intestine of fish raised in waste stabilization ponds in a sewage treatment plant. Samples of water and sludge were collected from all the selected ponds and were monitored for total counts of fecal coliform (FC), total coliform (TC) and the population of Escherichia coli, which was also obtained from the intestine of fishes. Total counts of both FC and TC as well as counts of E. coli were markedly reduced from the facultative pond to the last maturation pond. Tolerance limit to cadmium by E. coli tended to decline as the distance of the sewage effluent from the source increased; the effective lethal concentration of cadmium ranged from 0.1 mM in split chamber to 0.05 mM in first maturation pond. E. coli isolated from water, sludge and fish gut were sensitive to seven out of ten antibiotics tested. It appears that holistic functions mediated through the mutualistic growth of micro algae and heterotrophic bacteria in the waste stabilization ponds were responsible for the promotion of water quality and significant reduction of coliform along the sewage effluent gradient.

Cadmium tolerance and antibiotic resistance of Pseudomonas sp. isolated from water, sludge and fish raised in wastewater-fed tropical ponds.

The numbers of Pseudomonas sp. isolated were counted in samples collected from water, sludge and intestine of fishes raised in different wastewater ponds along an effluent gradient in a sewage treatment plant. Total fish yield in the last maturation pond increased by 73% over the yield in first maturation pond or facultative pond. The number of Pseudomonas sp. isolated from the intestine of the tilapia (Oreochromis mssambicus) raised in facultative pond, was more than three times the counts (7.22 × 108/g) observed in the last maturation pond (2.025 × 108/g). The effective lethal concentration of cadmium for Pseudomonas sp. isolated from the intestine of the tilapia was 0.6 mM and 0.08-0.09 mM when the fish was procured from facultative pond and last maturation pond, respectively. The Pseudomonas sp. isolated from the intestine of the tilapia did not have resistance to any of the ten antibiotics tested. However, the bacterium isolated from raw sewage, water and sediment of the anaerobic pond was resistant to seven out of ten antibiotics tested.