Many human diseases are caused by pathogens that produce exotoxins. The genes that encode these exotoxins are frequently encoded by mobile DNA elements such as plasmids or phage. Mobile DNA elements can move exotoxin genes among microbial hosts, converting avirulent bacteria into pathogens. Phage and bacteria from water, soil, and sediment environments represent a potential reservoir of phage- and plasmid-encoded exotoxin genes. The genes encoding exotoxins that are the causes of cholera, diphtheria, enterohemorrhagic diarrhea, and Staphylococcus aureus food poisoning were found in soil, sediment, and water samples by standard PCR assays from locations where the human diseases are uncommon or nonexistent. On average, at least one of the target exotoxin genes was detected in approximately 15% of the more than 300 environmental samples tested. The results of standard PCR assays were confirmed by quantitative PCR (QPCR) and Southern dot blot analyses. Agreement between the results of the standard PCR and QPCR ranged from 63% to 84%; and the agreement between standard PCR and Southern dot blots ranged from 50% to 66%. Both the cholera and shiga exotoxin genes were also found in the free phage DNA fraction. The results indicate that phage-encoded exotoxin genes are widespread and mobile in terrestrial and aquatic environments.

译文

:许多人类疾病是由产生外毒素的病原体引起的。编码这些外毒素的基因通常由可移动的DNA元件(如质粒或噬菌体)编码。可移动的DNA元素可以在微生物宿主之间移动外毒素基因,从而将无毒细菌转化为病原体。来自水,土壤和沉积物环境的噬菌体和细菌代表着噬菌体和质粒编码的外毒素基因的潜在库。通过标准PCR检测在人类疾病不常见或不存在的地方的土壤,沉积物和水样中发现了编码霍乱,白喉,肠出血性腹泻和金黄色葡萄球菌食物中毒的外毒素编码基因。平均而言,在所测试的300多个环境样本中,大约有15%检测到了目标外毒素基因中的至少一种。通过定量PCR(QPCR)和Southern点印迹分析证实了标准PCR测定的结果。标准PCR和QPCR结果之间的一致性介于63%至84%之间;标准PCR和Southern点印迹的一致性介于50%至66%之间。在游离噬菌体DNA部分中也发现了霍乱和志贺外毒素基因。结果表明,噬菌体编码的外毒素基因在陆地和水生环境中广泛存在并且可以移动。

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