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Recognized as a mobile genetic element, integron is correlated to the excision and integration of exogenous genes, especially bacterial resistance genes. However, most of the investigations focused on Gram-positive bacteria with few exceptions. In this study, Enterococcus faecalis was selected to investigate the excision and integration of class 1 integron. A total of eight plasmids were subjected to establish the transformants for excision and integration test. As results showed, positive excision assay was observed, which had been confirmed by the further integration assays and PCR amplification. The observation of class 1 integron mediated excision and integration of various exogenous antibiotics resistance genes should raise the attention of integrons as novel antibiotic resistance determinant in Gram-positive bacteria, especially in Enterococcus.

In this study, a number of frequently detected gene cassettes from bacterial integrons have been detected and characterized by rapid and simple loop-mediated isothermal amplification (LAMP) assays. Six gene cassettes commonly found in class 1 integrons were studied, including dfrA12, dfrA17, aadA2, aadA5, orfF, and blaVIM2. Primers design, sensitivity, specificity, optimization of each LAMP assay, as well as application of the developed 6 individual LAMP assays on a large scale of bacteria, had been conducted. The optimal amplification was obtained with temperature as 65 °C, reaction time span as 45 min and volume as 25 μl. For application, 272 isolates with various gene cassettes yielded expectable positive amplicons and other 685 integron-negative bacteria showed negative results for the LAMP assays, totaling 100% detection rate and specificity.