Bahl Martin Iain, Sørensen Søren J, Hansen Lars Hestbjerg, Licht Tine Rask
Department of General Microbiology, University of Copenhagen, 1307 Copenhagen K, Denmark.
Appl Environ Microbiol. 2004 Feb;70(2):758-64. doi: 10.1128/AEM.70.2.758-764.2004.
We have investigated the transfer of Tn916 among strains of Enterococcus faecalis OG1 colonizing in the intestines of gnotobiotic rats. This animal model allows a low limit of detection and efficient colonization of the chosen bacteria. The animals continuously received tetracycline in drinking water. A tetracycline-sensitive recipient strain was allowed to colonize the animals before the resistant donor was introduced. The numbers of donors, recipients, and transconjugants in fecal samples and intestinal segments were estimated. The bioavailable amounts of tetracycline in fecal samples and intestinal segments were monitored by using bacterial biosensors carrying a transcriptional fusion of a tetracycline-regulated promoter and a lacZ reporter gene. Chromosomal locations of Tn916 in transconjugants isolated either from the same animal or from different animals were compared by Southern blot analysis. Our results indicated that selection for the resistant phenotype was the major factor causing higher numbers of transconjugants in the presence of tetracycline. Tetracycline-sensitive E. faecalis cells colonized the intestine even when the concentrations of tetracycline in feces and intestinal luminal contents exceeded growth-inhibitory concentrations. This suggests the existence of tetracycline-depleted microhabitats in the intestinal environment.
我们研究了Tn916在定殖于无菌大鼠肠道中的粪肠球菌OG1菌株间的转移情况。这种动物模型能够实现对选定细菌的低检测限和高效定殖。动物持续饮用含四环素的水。在引入抗性供体之前，先让一株四环素敏感受体菌株定殖于动物体内。对粪便样本和肠段中的供体、受体及接合子数量进行了估算。通过使用携带四环素调控启动子与lacZ报告基因转录融合体的细菌生物传感器，监测了粪便样本和肠段中四环素的生物可利用量。通过Southern印迹分析比较了从同一动物或不同动物分离出的接合子中Tn916的染色体定位。我们的结果表明，在四环素存在的情况下，对抗性表型的选择是导致接合子数量增加的主要因素。即使粪便和肠腔内容物中四环素的浓度超过生长抑制浓度，四环素敏感的粪肠球菌细胞仍能在肠道中定殖。这表明肠道环境中存在四环素耗尽的微生境。
