Infections and Cystic Fibrosis Unit, IRCCS San Raffaele Scientific Institute, 20132 Milan, Italy.
Department of Biosciences, University of Milan, 20133 Milan, Italy.
Int J Mol Sci. 2017 Nov 14;18(11):2417. doi: 10.3390/ijms18112417.
is an important opportunistic pathogen in cystic fibrosis (CF) patients, and has also been isolated from natural environments. In previous work, we explored the virulence and pathogenic potential of environmental strains and demonstrated that they do not differ from clinical strains in some pathogenic traits. Here, we investigated the ability of the environmental Mex1 strain, isolated from the maize rhizosphere, to persist and increase its virulence after serial passages in a mouse model of chronic infection. Mex1 strain, belonging to the IIIA, was embedded in agar beads and challenged into the lung of C57Bl/6 mice. The mice were sacrificed after 28 days from infection and their lungs were tested for bacterial loads. Agar beads containing the pool of colonies from the four sequential passages were used to infect the mice. The environmental strain showed a low incidence of chronic infection after the first passage; after the second, third and fourth passages in mice, its ability to establish chronic infection increased significantly and progressively up to 100%. Colonial morphology analysis and genetic profiling of the Mex1-derived clones recovered after the fourth passage from infected mice revealed that they were indistinguishable from the challenged strain both at phenotypic and genetic level. By testing the virulence of single clones in the infection model, we found that two Mex1-derived clones significantly increased their pathogenicity compared to the parental Mex1 strain and behaved similarly to the clinical and epidemic LMG16656. Our findings suggest that serial passages of the environmental Mex1 strain in mice resulted in an increased ability to determine chronic lung infection and the appearance of clonal variants with increased virulence in non-vertebrate hosts.
是囊性纤维化 (CF) 患者的重要机会性病原体，也已从自然环境中分离出来。在之前的工作中，我们探讨了环境 株的毒力和致病潜力，并证明它们在一些致病特征上与临床株没有区别。在这里，我们研究了从玉米根际分离的环境 Mex1 株在慢性感染小鼠模型中连续传代后保持和增加其毒力的能力。 Mex1 株属于 IIIA 型，被嵌入琼脂珠中，并被挑战进入 C57Bl/6 小鼠的肺部。感染后 28 天，处死小鼠并检测其肺部细菌载量。用含有连续 4 次传代的 菌落的琼脂珠感染小鼠。环境 株在第一次传代后慢性感染的发生率较低；在第二次、第三次和第四次传代后，其建立慢性感染的能力显著且逐渐增加至 100%。对从感染小鼠中回收的经过第四次传代的 Mex1 衍生克隆进行菌落形态分析和遗传特征分析表明，它们在表型和遗传水平上与受挑战的菌株完全相同。通过在 感染模型中测试单个克隆的毒力，我们发现两个 Mex1 衍生克隆与亲本 Mex1 菌株相比显著增加了它们的致病性，并且与临床和流行的 LMG16656 相似。我们的研究结果表明，环境 Mex1 株在小鼠中的连续传代导致其确定慢性肺部感染的能力增加，并在非脊椎动物宿主中出现具有增加毒力的克隆变异体。
