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.

Responses of succinate dehydrogenase and non-specific alkaline phosphatases and mortality of tilapia to ambient pH stress in a sewage-fed aquaculture pond.

The fish, tilapia (Oreochromis mossambicus) of 50-60 g body weight was experimentally exposed to effluent gradients of highly alkaline pH in a sewage-fed aquaculture farm for examining the pH stress-induced responses of mortality and the stress marker enzyme succinate dehydrogenase and the non-specific alkaline phosphatases of fish prior to death at different hours of intoxication. A second trial was performed after two months when water quality changed along the sewage effluent gradient. An in situ experiment was also performed for better understanding of the responses of enzymatic activities attributable to different levels of pH conditions. Time required for 100% mortality of fish tended to increase from 30 min in pH 11.6 to 22 hr in pH 10.2. There was no mortality of fish when water quality improved significantly (with pH ranging between 9.6 to 8.0) after two months. The activities of succinate dehydrogenase and intracellular alkaline phosphatases assayed in gills and liver prior to death of fish tended to reduce with increase in survival hour, following a pattern of decay curve. On the other hand, percent of enzymatic inhibition of the exposed fish over the control increased as the survival hour increased following a pattern of exponential curve. It appears that the highest water pH of 11.6. maximum ratio for ammonium to ammonium hydroxide (1: 21) and reduced level of dissolved oxygen (2.62 mg/l) were perhaps responsible for the 100% mortality of fish within 30 min of their exposure and the enzymatic activities in the gills and liver assayed prior to death of fish tended to reduce as the acclimatization period of fish increased and vice-versa.

Oxygen uptake and filtration rate as animal health biomarker in Lamellidens marginalis (Lamarck).

The freshwater bivalve, L. marginalis was experimentally exposed to 10 and 30 ppm concentrations of CdCl2 to examine filtration rate, oxygen uptake and glycogen level of liver and gills for health assessment for their reuse in the reclamation of cadmium intoxicated environments. In situ experiment was also performed for better appraisal of the filtration rate in the lake. Oxygen uptake in the treated group exceeded that of control by 15-22% during the early 24 hr after cadmium exposure, but followed an essential decline (23-30%) thereafter. The reduction of filtration rate ranged from 12-62% in laboratory to 83-85% in field trials. At the tissue level, glycogen content was reduced by 61-72% in liver and 52-63% in gill. In both tissues, glycogen content was inversely proportional to the cadmium contents of the animal. Critical appraisal of data suggests that the threshold values of cadmium in gill and liver were 50-80 microg/g dw for oxygen uptake and 50-60 microg/g for filtration rate because of marked reduction of these parameters beyond the values of cadmium. It is concluded that filtration rate, oxygen uptake of the freshwater bivalve, L. marginalis can be used as biomarker for animal health assessment and for possible reuse of the stock animals.