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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.

The intestinal bacteria are known to play a significant role in intestinal homoeostasis and the mucosal immune system. In vitro interactions of Ampicillin (0.5-2.0 mg mL À1 ), Amphotericin-B (25-200 mg mL À1 ) and Ciprofloxacin (50-500 ng mL À1 ) with Escherichia coli, Pseudomonas sp. (Gram-negative), Lactobacillus sp., Staphylococcus sp. (Gram-positive), total mixed population of gut bacteria and intestinal epithelial cells were studied. In vitro exposure of Ciprofloxacin showed significant dose-dependent inhibition throughout the growth phase in bacteria. Similar patterns of concentration-dependent changes in membrane transport enzymes and structural constituents, dehydrogenase activity associated with respiratory and energy-producing processes and esterase activity test linked to the general heterotrophic activity of the cell were observed in both bacteria and epithelial cells. The antibiotic effects were in the order of Amphotericin-B o Ampicillin o Ciprofloxacin. Validation studies were conducted using rat intestinal loops filled with different concentrations of antibiotics and incubated for 30 min. In situ changes in epithelial cell membrane enzymes and constituents also indicated similar trends as observed following in vitro exposures. The findings suggest that these antibiotics exert similar cytotoxic effects on intestinal epithelial cells and gut bacteria. Thus, gut bacteria can be used for in vitro screening of gastrointestinal-cellular toxicity caused by antibiotics.

Chromium is a toxic heavy metal, which primarily exists in two inorganic forms, Cr (VI) and Cr (III). Highly soluble hexavalent chromium is carcinogenic due to its oxidizing nature. It is well established that the intestinal bacteria including Lactobacilli have regulatory effect on intestinal homeostasis and a breakdown in the relationship between intestinal cells and bacteria results in the manifestation of gastrointestinal (GI) disorders. In this study Cr (VI) resistance was developed in Lactobacillus strains and the reduction of Cr (VI) was evaluated. All resistant strains showed similarities with their respective normal strains and did not acquire resistance to various antibiotics. A complete bacterial reduction of 32ppm Cr (VI) was observed within 6 to 8 hours. The presence of chromate reducing enzyme have also been established following the partial purification (2 to 5 fold) and characterization of chromate reductase in Lactobacillus strains. The chromate reductase of our strains showed optimum activity at pH 6.0 and 30°C. To our knowledge; these strains are fast in Cr (VI) reduction than any other known bacteria. The results suggest that chromate- resistant Lactobacillus strains would be useful for chromium detoxification from GI-tract as well as for bioremediation of hexavalent chromium from contaminated environment.

Aspirin, a commonly used therapeutic non-steroidal anti-inflammatory drug (NSAID) is known to cause gastric mucosal damage. Intestinal bacteria having a regulatory effect on intestinal homeostasis play significant role in NSAID-induced intestinal injury. Bacteria and specific cell lines are considered to be suitable for toxicity screening and testing of chemicals. Therefore, to evaluate and compare in vitro toxicity, cultures of rat intestinal epithelial cells (IEC), isolated bacteria and IEC-6 cell line were assessed for viability, morphometric analysis, membrane transport enzymes and structural constituents for membrane damage, dehydrogenase activity test for respiratory and energy producing processes and esterase activity test for intra- and extra-cellular degradation, following the post exposure to aspirin (0—50 µg mL- 1). Similar pattern of dose-dependent changes in these parameters were observed in three types of cells. Similar in situ effects on IEC validated the in vitro findings. These findings indicate that higher aspirin concentrations may alter cellular functions of IEC and gut bacteria. Furthermore, results suggest that gut bacteria and IEC-6 cell line can be used for the initial screening of gastrointestinal cellular toxicity caused by NSAIDs.