Grazing protozoa and the evolution of the Escherichia coli O157:H7 Shiga toxin-encoding prophage
Grazing protozoa and the evolution of the Escherichia coli O157:H7 Shiga toxin-encoding prophage
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DOI：
10.1098/rspb.2007.0245
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发表时间：
2007-08-22
影响因子：
4.7
通讯作者：
Levin, Bruce R.
中科院分区：
文献类型：
--
作者：
Meltz Steinberg, Karyn;Levin, Bruce R.
人类在大肠杆菌O157: H7（牛的一种共生细菌）的流行病学中起不到什么作用。那么，为什么大肠杆菌O157: H7编码毒力决定因素，如志贺毒素（Stxs），导致定殖人类的发病率和死亡率？一种可能性是，这些细菌对人类的毒力是巧合，这些毒力因子的进化和维持是为了它们在这些细菌的生态中扮演的其他角色。在这里，我们验证了大肠杆菌O157: H7携带stx编码的原噬菌体在放牧原生动物梨形四膜虫存在下提高大肠杆菌存活率的假设。在有四膜虫存在但不存在的情况下，携带编码stx的前噬菌体通过增加细菌在这些纤毛虫的食物液泡中的存活率，大大增加了大肠杆菌K-12和大肠杆菌O157的临床分离株的适应性。环境或天然宿主中的食草原生动物可能在大肠杆菌O157:H7编码stx的前噬菌体的生态和维持中发挥重要作用，并可能很好地促进这些细菌的毒力进化以定植人类。
Humans play little role in the epidemiology of Escherichia coli O157: H7, a commensal bacterium of cattle. Why then does E. coli O157: H7 code for virulence determinants, like the Shiga toxins (Stxs), responsible for the morbidity and mortality of colonized humans? One possibility is that the virulence of these bacteria to humans is coincidental and these virulence factors evolved for and are maintained for other roles they play in the ecology of these bacteria. Here, we test the hypothesis that the carriage of the Stx-encoding prophage of E. coli O157: H7 increases the rate of survival of E. coli in the presence of grazing protozoa, Tetrahymena pyriformis. In the presence but not the absence of Tetrahymena, the carriage of the Stx-encoding prophage considerably augments the fitness of E. coli K-12 as well as clinical isolates of E. coli O157 by increasing the rate of survival of the bacteria in the food vacuoles of these ciliates. Grazing protozoa in the environment or natural host are likely to play a significant role in the ecology and maintenance of the Stx-encoding prophage of E. coli O157:H7 and may well contribute to the evolution of the virulence of these bacteria to colonize humans.