Conditional DNA excision between two LoxP sites can be achieved in the mouse using Cre-ERT, a fusion protein between a mutated ligand binding domain of the human estrogen receptor (ER) and the Cre recombinase, the act...
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Conditional DNA excision between two LoxP sites can be achieved in the mouse using Cre-ERT, a fusion protein between a mutated ligand binding domain of the human estrogen receptor (ER) and the Cre recombinase, the activity of which can be induced by 4-hydroxy-tamoxifen (OHT), but not natural ER ligands, We have recently characterized a new ligand-dependent recombinase, Cre-ERT2, which was similar to 4-fold more efficiently induced by OHT than Cre-ERT in cultured cells. In order to compare the in vivo efficiency of these two ligand-inducible recombinases to generate temporally-controlled somatic mutations, we have engineered transgenic mice expressing a LoxP-flanked (floxed) transgene reporter and either Cre-ERT or Cre-ERT2 under the central of the bovine keratin 5 promoter that is specifically active in the epidermis basal cell layer. No background recombinase activity could be detected, while recombination was induced in basal keratinocytes upon OHT administration. Interestingly, a dose-response study showed that Cre-ERT2 was similar to 10-fold more sensitive to OHT induction than Cre-ERT.
Background. Despite widespread use of potent antibiotics, infections of artificial implants and catheters are of increasing concern. We tested whether local treatment with 3% hydrogen peroxide (H2O2), long known as an...
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Background. Despite widespread use of potent antibiotics, infections of artificial implants and catheters are of increasing concern. We tested whether local treatment with 3% hydrogen peroxide (H2O2), long known as an inexpensive wound disinfectant, could prevent or reduce bacterial growth on polymer biomaterials. Methods. Two-centimeter-long pieces of polyurethane and silicone tubing were contaminated with a standardized solution of Staphylococcus epidermidis (10(5)/mL) and then rinsed and wiped with saline (0.9%) solution. Bacterial growth was assessed after incubation at 37 degrees C for 24 hours. Bacterial colonies were compared for the following treatments: wiping only with saline;wiping with 1.5%, 2%, or 3% H2O2;pretreating biomaterials with 3% H2O2 and subsequent contamination for 2 and 4 hours without treatment after contamination;and contamination of tubings I month after pretreatment with 30% H2O2. The effect of 3% H2O2 was also assessed on contamination with Escherichia coli. Results. Bacterial growth was reduced by more than 99% when the contaminated tubes were treated with 3% H2O2 compared with saline control (p < 0.001). Lower concentrations of H2O2 were less effective. The length of the contamination period had no influence on the effectiveness of H2O2 when used on polyurethane but did with silicone tubings. Pretreatment with H2O2 1 month before contamination still reduced bacterial growth rate by 90% on polyurethane and by 75% on silicone tubings. Comparable effects on bacterial growth rate were observed for staphylococci (-90%, p < 0.001) and escherichiae (-90%, p < 0.001). Conclusions. Local treatment with 3% H2O2 significantly reduced bacterial growth on polymer biomaterials even for I month after treatment. This finding might influence clinical strategies of prevention of foreign body infection. (C) 1999 by The Society of Thoracic Surgeons.
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