Involvement of surface polysaccharides in the organic acid resistance of Shiga Toxin-producing Escherichia coli O157:H7
Involvement of surface polysaccharides in the organic acid resistance of Shiga Toxin-producing Escherichia coli O157:H7
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DOI：
10.1046/j.1365-2958.2002.02768.x
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发表时间：
2002-02-01
影响因子：
3.6
通讯作者：
Ohta, M
中科院分区：
文献类型：
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作者：
Barua, S;Yamashino, T;Ohta, M
一般来说，野生大肠杆菌菌株可以在中等酸性的富含有机酸的条件下有效生长。我们发现产生滋贺毒素的E.大肠杆菌（STEC）O 157：H7 NGY 9在补充有乙酸（pH 5.4）的Luria-Bertani（LB）-2-吗啉代乙磺酸（MES）肉汤中比K-12菌株生长更快。假设STEC O 157：H7对乙酸的抗性是由于已知机制以外的机制，我们筛选了对乙酸敏感的STEC突变体。NGY 9进行mini-Tn 5诱变，从50000个菌落中分离出5个显示出明显乙酸敏感表型的突变体。mini-Tn 5的插入分别发生在fcl、wecA（rfe）和wecB（rffE）基因上，并分别导致表面O-多糖的缺失、O-多糖和肠杆菌共同抗原（ECA）的缺失以及ECA的缺失。另外两个突变体显示waaG（rfaG）基因的失活，但在不同的位置，导致了一个深粗糙突变体的外核心寡糖的脂多糖（LPS）的损失，以及表型的损失O-多糖和ECA。随着分别携带fcl、wecA、wecB和waaG基因的质粒的引入，所有突变体在它们的O-多糖和ECA生产中得到补充，并且在富含有机酸的培养条件下恢复正常生长。我们还发现，沙门氏菌LPS突变体Ra，Rb 1，Rc，Rd 1，Rd 2和Re的生长抑制在乙酸的存在下，与父母相比。这些结果表明，LPS（包括O-多糖）和ECA的充分表达是STEC O 157：H7和沙门氏菌对乙酸和其他短链脂肪酸的抗性所必需的。据我们所知，这是一个新确定的生理作用的O-多糖和ECA以及耐酸机制。
In general, wild Escherichia coli strains can grow effectively under moderately acidic organic acid-rich conditions. We found that the Shiga Toxin-producing E. coli (STEC) O157:H7 NGY9 grows more quickly than a K-12 strain in Luria-Bertani (LB)-2-morpholinoethanesulphonic acid (MES) broth supplemented with acetic acid (pH 5.4). Hypothesizing that the resistance of STEC O157: H7 to acetic acid is as a result of a mechanism(s) other than those known, we screened for STEC mutants sensitive to acetic acid. NGY9 was subjected to mini-Tn5 mutagenesis and, from 50 000 colonies, five mutants that showed a clear acetic acid-sensitive phenotype were isolated. The insertion of mini-Tn5 in three mutants occurred at the fcl, wecA (rfe) and wecB (rffE) genes and caused loss of surface O-polysaccharide, loss of both O-polysaccharide and enterobacterial common antigen (ECA) and loss of ECA respectively. The other two mutants showed inactivation of the waaG (rfaG) gene but at different positions that caused a deep rough mutant with loss of the outer core oligosaccharide of lipopolysaccharide (LPS) as well as phenotypic loss of O-polysaccharide and ECA. With the introduction of plasmids carrying the fcl, wecA, wecB and waaG genes, respectively, all mutants were complemented in their production of O-polysaccharide and ECA, and normal growth was restored in organic acid-rich culture conditions. We also found that the growth of Salmonella LPS mutants Ra, Rb1, Rc, Rd1, Rd2 and Re was suppressed in the presence of acetic acid compared with that of the parents. These results suggest that the full expression of LPS (including O-polysaccharide) and ECA is indispensable to the resistance against acetic acid and other short chain fatty acids in STEC O157:H7 and Salmonella. To the best of our knowledge, this is a newly identified physiological role for O-polysaccharide and ECA as well as an acid resistance mechanism.