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Toxicants including heavy metals reaching the intestine following ingestion through food and water primarily interact with an ecosystem of eukaryotic and prokaryotic cells. Gut bacteria having a dynamic interrelationship with intestinal epithelial cells are known to play important and specific metabolic, trophic, and protective functions. The present study was undertaken to compare the effects of hexavalent chromium on rat intestinal epithelial cells and the resident gut bacteria following in vitro and in vivo exposures. The survival rate and viability pattern of two types of cells were comparable. Under in vitro conditions, the gut bacteria were quick to reduce Cr (VI) in early time periods, while, at 30 h time, both types of cells showed similar capacity for the reduction of Cr (VI). Chromium intoxication (10 ppm of Cr (VI) in drinking water for 10 weeks) caused significant decrease in membrane alkaline phosphatase and Ca(2 +)-Mg(2 +)-ATPase activities of intestinal epithelial cells as well as of three gut bacteria viz. Escherichia coli, Pseudomonas sp, and Lactobacillus sp. Major structural membrane constituents like carbohydrates and phospholipids also showed significant decline in both types of cells. These findings indicate that 10 ppm and higher Cr concentrations may cause toxic insult, resulting in impaired intestinal functional efficacy. It also implies that the gut bacteria can be used at least for preliminary screening of heavy metals gastrointestinal toxicity.

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The major nonoccupational source of chromium (Cr) for humans is through ingestion with food and water, but its effect on the gut microflora has not been studied. The present study was, therefore, undertaken to investigate the effects of chronic ingestion of potassium dichromate (chromium VI) on the resident gut bacteria of male Wistar rats. A group of rats was kept on drinking water containing 10 ppm chromium VI (Cr [VI]) (called Cr-stressed animals) and the other group was given plain water. After 10 weeks, Lactobacillus, Pseudomonas sp., and Escherichia coli were isolated from the cecum of the rats and various studies were performed. The most significant findings of the present study were the stimulation of growth of facultative gut bacteria from the Cr-stressed rats and the significant increase of growth even in the presence of lower concentrations of Cr. Furthermore, the capacity to reduce Cr (VI) was significantly decreased along with the increased tolerance of the bacteria to Cr (higher minimum inhibitory concentration [MIC] values), which was associated with the development of antibiotic resistance. The effects were most marked with the Pseudomonas sp. and least with the E. coli. The antibiotic resistance developed with the Lactobacillus may be a blessing in disguise, because the bacteria may continue to provide benefits even in patients given antibiotic therapy. The gut bacteria thus provide the first line of defense to the body by converting toxic Cr (VI) to a less toxic Cr (III) and may act as a prebiotic.