高温联合紫外线照射增强了大肠杆菌 O157:H7 中 stx2 基因向非致病性大肠杆菌的水平转移。
High temperature in combination with UV irradiation enhances horizontal transfer of stx2 gene from E. coli O157:H7 to non-pathogenic E. coli.
机构信息
Department of Animal Science, University of Wyoming, Laramie, Wyoming, United States of America.
出版信息
PLoS One. 2012;7(2):e31308. doi: 10.1371/journal.pone.0031308. Epub 2012 Feb 9.
BACKGROUND
Shiga toxin (stx) genes have been transferred to numerous bacteria, one of which is E. coli O157:H7. It is a common belief that stx gene is transferred by bacteriophages, because stx genes are located on lambdoid prophages in the E. coli O157:H7 genome. Both E. coli O157:H7 and non-pathogenic E. coli are highly enriched in cattle feedlots. We hypothesized that strong UV radiation in combination with high temperature accelerates stx gene transfer into non-pathogenic E. coli in feedlots.
METHODOLOGY/PRINCIPAL FINDINGS: E. coli O157:H7 EDL933 strain were subjected to different UV irradiation (0 or 0.5 kJ/m(2)) combination with different temperature (22, 28, 30, 32, and 37 °C) treatments, and the activation of lambdoid prophages was analyzed by plaque forming unit while induction of Stx2 prophages was quantified by quantitative real-time PCR. Data showed that lambdoid prophages in E. coli O157:H7, including phages carrying stx2, were activated under UV radiation, a process enhanced by elevated temperature. Consistently, western blotting analysis indicated that the production of Shiga toxin 2 was also dramatically increased by UV irradiation and high temperature. In situ colony hybridization screening indicated that these activated Stx2 prophages were capable of converting laboratory strain of E. coli K12 into new Shiga toxigenic E. coli, which were further confirmed by PCR and ELISA analysis.
CONCLUSIONS/SIGNIFICANCE: These data implicate that high environmental temperature in combination with UV irradiation accelerates the spread of stx genes through enhancing Stx prophage induction and Stx phage mediated gene transfer. Cattle feedlot sludge are teemed with E. coli O157:H7 and non-pathogenic E. coli, and is frequently exposed to UV radiation via sunlight, which may contribute to the rapid spread of stx gene to non-pathogenic E. coli and diversity of shiga toxin producing E. coli.
背景
志贺毒素（stx）基因已转移到许多细菌中，其中之一是大肠杆菌 O157:H7。人们普遍认为，stx 基因是通过噬菌体转移的，因为 stx 基因位于大肠杆菌 O157:H7 基因组中的 lambdoid 前噬菌体中。大肠杆菌 O157:H7 和非致病性大肠杆菌在牛饲养场中高度富集。我们假设，强烈的紫外线辐射与高温相结合，加速了 stx 基因向饲养场中非致病性大肠杆菌的转移。
方法/主要发现：将大肠杆菌 O157:H7 EDL933 菌株暴露于不同的紫外线照射（0 或 0.5 kJ/m2）与不同的温度（22、28、30、32 和 37°C）处理相结合，并通过噬菌斑形成单位分析 lambdoid 前噬菌体的激活，通过定量实时 PCR 定量诱导 Stx2 前噬菌体。数据表明，大肠杆菌 O157:H7 中的 lambdoid 前噬菌体，包括携带 stx2 的噬菌体，在紫外线照射下被激活，这一过程在温度升高时得到增强。一致地，Western 印迹分析表明，紫外线照射和高温也显著增加了志贺毒素 2 的产生。原位菌落杂交筛选表明，这些激活的 Stx2 前噬菌体能够将实验室大肠杆菌 K12 株转化为新的产志贺毒素大肠杆菌，通过 PCR 和 ELISA 分析进一步证实了这一点。
结论/意义：这些数据表明，高温与紫外线照射相结合，通过增强 Stx 前噬菌体诱导和 Stx 噬菌体介导的基因转移，加速了 stx 基因的传播。牛饲养场污泥中充斥着大肠杆菌 O157:H7 和非致病性大肠杆菌，并且经常通过阳光暴露于紫外线辐射下，这可能导致 stx 基因迅速传播到非致病性大肠杆菌和产志贺毒素大肠杆菌的多样性。
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