The Effect of Persistent Heavy Metal Exposure on Some Antioxidant Enzyme Activities and Lipid Peroxidation of the Freshwater snail, Lymnaea natalensis.

This study investigated the effect of persistent heavy metal exposure on the activity of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) of the freshwater snail, Lymnaea natalensis. Malondialdehyde (MDA) levels were also measured as an index of lipid peroxidation. The snails were exposed to cadmium, copper, lead and mercury for a total of 28 days at 0.1 mg/L, 0.1 mg/L, 0.2 mg/L and 0.1 mg/L respectively. Samples were collected at 1, 7, 14, 21 and 28 days intervals. Analysis of SOD showed significant initial increases in enzyme activity following exposure to copper, lead and mercury, while cadmium exposures caused increases from Day 14 onwards. Copper, cadmium and lead caused significant initial increases in CAT activity and mercury caused an increase only on Day 28. Copper caused a significant increase in GPx activity on Day 28 while MDA levels diminished significantly at Days 7-28. Similarly, cadmium caused significant increases of GPx activity on Day 28 whereas MDA levels were significantly reduced. Lead also caused a significant increase in GPx activity on Days 14-28 whilst no significant changes occurred in MDA levels. Mercury exposures caused significant increases in GPx activity on Days 7 and 21, whilst MDA levels were significantly reduced on Days 7 and 14. These findings suggest that persistent exposure of snails to heavy metals induces the antioxidant defence system, and decreases lipid peroxidation.

A comparison of metal levels and antioxidant enzymes in freshwater snails, Lymnaea natalensis, exposed to sediment and water collected from Wright Dam and Lower Mguza Dam, Bulawayo, Zimbabwe.

We compared the bioaccumulation of lead (Pb), cadmium (Cd), zinc (Zn), copper (Cu), nickel (Ni) and iron (Fe) with antioxidant enzyme activity in tissues of the snails, Lymnaea natalensis, exposed to elements of two differently polluted dams. 45 snails were exposed to sediment and water collected from Wight Dam (reference) whilst another 45 snails were also exposed to sediment and water collected from Lower Mguza Dam (polluted dam). Except for Fe in sediment and Pb in water, metal concentrations were statistically higher in sediment and water collected from Lower Mguza Dam. Lead, Cd and Zn were two times higher in tissues of snails exposed to Lower Mguza Dam elements. On one hand, superoxide dismutase (SOD), diphosphotriphosphodiaphorase (DTD) and catalase (CAT) activities were significantly lower whilst malondialdehyde (MDA) levels were significantly higher in tissues of snails exposed to Lower Mguza Dam sediment and water. On the other hand, selenium-dependent glutathione peroxidase (Se-GPX) activity was significantly elevated in tissues of snails exposed to Lower Mguza Dam sediment and water. Snails exposed to Lower Mguza Dam elements seem to have responded to pollution by increasing CAT and Se-GPX specific activity in an effort to detoxify peroxides produced as a result of metal induced oxidative stress.

Metal accumulation and antioxidant enzyme activity in C. gariepinus, catfish, and O. mossambicus, tilapia, collected from Lower Mguza and Wright Dams, Zimbabwe.

The aim of this study was to measure antioxidant enzyme activities as biological indicators of pollution in tissues of two species of fish. Five Clarius gariepinus and three Oreochromis mossambicus were collected from Umguza Dam (polluted dam) whilst seven C. gariepinus and eight O. mossambicus were collected from Wright Dam (relatively pristine dam). Diphosphotriphoshodiaphorase and catalase activities were consistently lower (42 +/- 2% and 78 +/- 20%, respectively) in liver whilst malondialdehyde levels were two times higher in muscles of both species of fish collected from Umguza Dam. However, seleniumdependent glutathione peroxidase (Se-GPX) activity was elevated four-fold in liver and gills of O. mossambicus collected from Umguza Dam. Metal levels were two to five times higher in muscles of both species of fish collected from Umguza Dam. Fish from Umguza Dam seem to have responded to pollution by increasing Se-GPX specificactivity in an effort to detoxify peroxides produced as a result of metal induced oxidative stress.

A comparison of antibiotic resistance in microorganisms isolated from chicken and ostrich faeces in Bulawayo; Zimbabwe

Samples of fresh faeces were obtained from a free-range chicken source; three commercial chicken farms and a commercial ostrich farm; all located around Bulawayo City; Zimbabwe; in order to determine the antibiotic resistance profile of selected bacterial isolates of interest in food-related human infections. Samples were prepared at various dilutions and plated on selective media for Coryneforms; Escherichia coli; Enterococcus faecalis and Pseudomonas. The targeted bacteria were isolated as pure cultures and tested for antibiotic resistance to ampicillin; chloramphenicol; oxytetracycline; sulphonamide; streptomycin and tetracycline. Isolates from the faeces of chickens and ostriches in the commercial farms were found to be generally more resistant to streptomycin; tetracycline and oxytetracycline as compared to those from the free- range chickens. This study emphasizes the need to monitor antibiotic resistance genes in the environment and to curb/curtail antibiotic use for growth promotion in farm animals; particularly in developing countries; as continued use will only add to the growing problem of microbial antibiotic resistance

The effect of schistosomiasis on the covalent binding of 2-acetylaminofluorene to mouse liver macromolecules in vivo and in vitro.

The covalent binding of [14C]acetylaminofluorene (AAF) to macromolecules in vivo and in vitro was measured in Schistosoma mansoni-infected and in non-infected mice. Liver microsomes from infected mice demonstrated a 42% decreased capacity to mediate covalent binding of AAF to DNA. In addition, the extent of binding of AAF to liver macromolecules in vivo was generally less in infected than non-infected mice.

The effect of schistosomiasis on the activation of aflatoxin B1.

This study examined activation of aflatoxin B1 (AFB1) in livers of Schistosoma mansoni-infected and noninfected mice by measuring covalent binding of [3H]AFB1 to cellular macromolecules in vivo and in vitro. During a one week time period after AFB1 treatment of animals, maximal binding of [3H]AFB1 to DNA, RNA and protein in liver occurred during the 1-6 hour period after treatment, with less binding throughout of AFB1 to macromolecules of infected mice. Experiments performed in vitro to determine the capacity of liver microsomes to mediate the binding of AFB1 to calf thymus DNA showed that microsomes from infected mice mediated the binding of less [3H]AFB1 to DNA than those from noninfected animals.