华东地区部分猪源大肠杆菌K 88黏附素的生物学特性

Identification of K88ac Fimbrial Antigen of Enterotoxigenic Escherichia coli Iso-lated from Diarrhoeal Piglets in Eastern of China

近年来,从华东地区患腹泻仔猪中分离到一些表达K 88菌毛的大肠杆菌,这些菌株只与K 88 a因子单抗反应,而不与b、c、d因子单抗反应。通过K 88常规血清交叉吸收试验、SDS-PAGE、W estern印迹,表明这些菌株不仅与K 88ac参考菌株C 83907制备的c因子血清反应,而且与以分离株SEC 586制备且经K 88ab、K 88ac、K 88ad参考菌株吸收后的血清也反应。对分离株SEC 586、SEC 464的K 88主要亚单位结构基因faeG的克隆、测序,发现该基因由846对核苷酸组成,编码菌毛主要亚单位的262个氨基酸及21个氨基酸的信号肽,比国外报道的K 88ac F aeG亚单位(263个氨基酸)少了1个氨基酸,比K 88ab、K 88ad(265个氨基酸)少了3个氨基酸。SEC 586、SEC 464菌株的F aeG亚单位氨基酸序列的同源性为97.7%,它们与K 88ac的同源性为94.7%和96.2%;与K 88ab的同源性为90.1%和91.2%;与K 88ad的同源性为87.0%和88.6%。结果表明,新分离的K 88ac大肠杆菌黏附素主要亚单位已发生了部分变异。

Some E. coli strains from newborn piglets with diarrhoea were isolated in the eastern regions of China during 2000 to 2003. They reacted with K88-a specific monoclonal antibody while not with K88-b,c,d specific monoclonal antibodies in the slide agglutination test. These isolates were identified with K88ac variant by cross-absorbed rabbit antisera to K88ac fimbria. The apparent molecular weight of K88ac antigens purified from these isolates was about 26 000 in SDS-PAGE, and experienced a positive reaction with the rabbit antisera absorbed with K88ac reference strain in Western blot. The faeG genes were amplified from the genomic DNA of these isolates by PCR. The PCR product of faeG was cloned into pGEM-T vector. Alignment analysis of major FaeG subunits of the K88ac fimbria of these isolates showed some differences in amino acid composition as compared with those of K88ac reference strains, implying that the antigenic differences between these isolates and reference strains may be owing to the mutation of major subunits of the fimbria. Comparison of the sequences of amino acids of the major units showed that the percent identity was 97.7 % between isolate SEC586 and isolate SEC464 in amino acid sequences of major subunit FaeG, and 90. 1% and 91. 2% comparing with K88ab reference strains, 94. 7% and 96. 2% with K88ac reference strains, 87.0% and 88.6% with K88ad reference strains, respectively. These results revealed that K88ac fimbrial antigens of these ETEC isolates experienced some variations as compared with those of K88ac reference strains.