| Soybean isoflavones (SI) are the secondary metabolites mainly composed by isoflavone daidzein and genistein. SI are degraded into equol and O-desmethylangolensin (O-Dma) by intestinal microflora in gastra intestinal tract after being absorbed. At present, among all SI metabolites, equol shows the highest bioactivity.However, SI biotransforming microflora are being influeced by many factors, such as dietary habits, age, disease, use of antibiotic, and many other factors and so on.In this paper, ICR mice were used as experimental animals since their gut microflora can transforme daidzein into dihydrodaidzein(DHD) and equol stablely. The effects of different antibiotics on the biotransformation of daidzein into equol by intestinal microflora of ICR mice in vitro were investigated. In order to provide some guidance for rational useage of antibiotics for human beings, the critical inhibitory concentrctions of sonsitire antibiobics were determined as well.This is the first study of the influence of different antibiotics on transformation activicty of isoflance by intestinet microflora of ICR mice. All eleven kinds of antibiotics showed completely inhibitive effects on the bioconversion of daidzein into equol under normal adult dose. Three types of antibiotics including amoxicillin, ofloxacin and norfloxacin had no effects under the concentration of 1/32 normal adult dose. On the contrary, another five antibiotics including azithromycin, leucomycin, oxytetracycline, rifampicin, and metronidazole totally inhibited the biotransforming capacity of the intestinal microflora of ICR mice under the same concentration. The biosynthesized equol from daidzein was detected to decrease 87.7%,80.5% and 65.2%, respectively when the same concentration of doxycycline, erythromycin and cephradine was used. Under the concentration of 1/256 normal adult dose, three antibiotics including azithromycin, rifampicin and metronidazole showed completely inhibitive effects. The lowest inhibitive concentration of the three sensitive antibiotics mentioned above were 1/512,1/800 and 1/1024, respectively.Gram positive bacterial strain Niu-O16(AY263505) isolated from bovine rumen gastric juice is capable of biotransforming daidzein into DHD. In order to study whether bacterial strain Niu-016 was able to combine in gastrointestinal tract of ICR mice or not, the tested ICR mice were treated with sensitive antibiotics determined by in vitro experimats till their daidzein biotransformation activity was totally inhibited. In order to protect bceterial strain Niu-016 from being damaged by low-pH gastric juice of ICR mice, strain Niu-016 were wrapped into sodium microcapsules are not broken or melted in simulated gastric juice, however they can break down by simulated intestinal microcapsules witsowt bacterial stain Niu-016 were anatomy. In order to know whether such kind of microcapsules will experience similer procedures as that of in vitro experiments. The feces of tested ICR mice were collected for detection of eliminated microcapsules after being fed with microcapsules. But no microcapsules were found in any feces. At necropsy, there were a lot of microcapsules in ICR mouse stomach after 2 hours, but in intestine none of the miorocapasules were found. Six hours later, all the microcapsules disappeared in stomach. Microcapsules were not found neither in stomach nor intestine after 12 hours. Since no microcapsules were found in either mice feces by anatoy, which illustratment that all microcapsules can break throw completely 12 hours.Since the daidzein biotransforming activity was able to be totally inhibited for just about two weeks by using antibiotics. The deteced concentred of DHD by microflora of tested mice fed with bacterial strain Niu-O16 was much higher than that of blank control, it is still not sure whether baeterial strain Niu-016 can plant in intestinal tract of ICR mice or not. A further study in needed to be done.
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