Parreira Valeria R, Liao Jing Hua, Kim Sang-Hyun, Gyles Carlton L
Department of Pathobiology, University of Guelph, Guelph, Ontario N1G 2W1, Canada.
Vet Res. 2008 May-Jun;39(3):38. doi: 10.1051/vetres:2008015. Epub 2008 Mar 4.
The relationship of the urease operon in the highly virulent O149 porcine enterotoxigenic Escherichia coli (ETEC) strain Ro8 to a genomic island (GI) homologous to O island (OI) 48 of O157 enterohemorrhagic E. coli (EHEC) strain EDL933 was investigated. Eighty-four of 84 O149:H10 strains were urease positive whereas 44 of 44 O149:H43 porcine ETEC strains were urease-negative. Seventeen of 17 O149:H10 strains that were tested possessed the OI-48 homolog whereas 24 of 24 O149:H43 strains lacked this OI. Transposon insertions in lipB or guaA genes in strain Ro8 eliminated urease activity while insertions in the caiF gene increased urease activity. When the O149 ure operon was cloned on a high copy number plasmid, urease expression was increased approximately 11-fold in Ro8 and 83-fold in O157 strain EDL933 compared with that in the wild type Ro8. The O149 urease activity was expressed despite the presence of the same premature stop codon in ureD that is present in ure+ O157:H7 strains that are urease-negative. The ure operon in Ro8 consists of 4 893 nucleotides with 99% identity with the ure operons in EHEC O157:H7 strains EDL933 and Sakai, and is part of a GI similar to GI-48 of strain EDL933. This OI, designated OI-48149 , is inserted in the serX tRNA gene in strain Ro8 and contains genes for urease, tellurite resistance, iha and an AIDA-I-like adhesin. The presence of a homolog of the O157:H7 OI-48 in highly virulent O149 porcine ETEC suggests that this OI may contribute to establishment of the bacteria in the intestine.
研究了高毒力O149猪产肠毒素大肠杆菌（ETEC）菌株Ro8中脲酶操纵子与一个与O157肠出血性大肠杆菌（EHEC）菌株EDL933的O岛（OI）48同源的基因组岛（GI）之间的关系。84株O149:H10菌株中有84株脲酶呈阳性，而44株O149:H43猪ETEC菌株中有44株脲酶呈阴性。所检测的17株O149:H10菌株中有17株拥有OI-48同源物，而24株O149:H43菌株中均缺乏该OI。Ro8菌株中lipB或guaA基因的转座子插入消除了脲酶活性，而caiF基因中的插入则增加了脲酶活性。当O149脲操纵子克隆到高拷贝数质粒上时，与野生型Ro8相比，Ro8中的脲酶表达增加了约11倍，O157菌株EDL933中增加了83倍。尽管在ureD中存在与脲酶阴性的ure+ O157:H7菌株中相同的提前终止密码子，但O149脲酶活性仍得以表达。Ro8中的脲操纵子由4893个核苷酸组成，与EHEC O157:H7菌株EDL933和Sakai中的脲操纵子有99%的同一性，并且是一个与菌株EDL933的GI-48相似的GI的一部分。这个OI被命名为OI-48149，插入到Ro8菌株的serX tRNA基因中，包含脲酶、亚碲酸盐抗性、iha和一个AIDA-I样黏附素的基因。高毒力O149猪ETEC中存在O157:H7 OI-48的同源物，表明该OI可能有助于细菌在肠道中的定植。
