致泻性大肠杆菌astA基因的分型与致病性研究

EAST1, a heat-stable enterotoxin, which is firstly detected in enteroaggregative E. coli, could cause diarrhea in human intestines though food poison. In the previous study, astA could exist in both plasmid and chromosome DNA, and effect the expression of EAST1 enterotoxin. The astA gene found in outbreak strains showed more diversity in nucleotide sequences than the ones in non-pathogenic strains, and carried multiple clones of astA gene with multiple amino acids changes at residues. However, the subtyping and the pathogenicity of astA gene, and the epidemiological role of EAST1 in human intestinal diseases was not clarified. In this study, we aim to classify the astA gene types of 446 strains isolated from foods, and animal and healthy carriers and patient feces by gene sequencing and protein modeling. The relationship between astA types and pathogenicity of strains will be clarified by using the multiple-locus variable number tandem repeats analysis method, combine with the data analysis of serotype identification, antimicrobial resistances and phythogenetic grouping characteristics. It will help to know the important role of astA in the epidemiologic studies of diarrheogenic E. coli.

EAST1是发现于肠黏附性大肠杆菌中的一种热稳定性肠毒素，是引起食源性腹泻的主要原因之一。前期研究表明，其编码基因astA广泛存在于致泻性大肠杆菌的质粒和染色体上并影响EAST1毒素的表达，且引起食物中毒菌株的astA基因具有多样性并在氨基酸残基上表现出更多的差异。然而多数研究因样本量小且菌株来源单一，导致astA基因的分型、致病性强弱以及与其在基因组中的位置关系尚不明确。本项目以食物、动物粪便及健康人和病人来源的446株致泻性大肠杆菌为研究对象，从基因表达和系统发育分析入手，研究astA基因的致病性差异，考察核苷酸序列和蛋白质空间构象之间的内在规律，分析其与基因位点的相互关联，运用统计学手段推测astA基因的合理分型。并结合菌株的血清型及耐药性特点，通过系统发育学方法解析不同基因分型菌株与致病菌株间的亲缘性，从而阐明astA基因分型与其致病性之间的关系。

EAST1是发现于肠黏附性大肠杆菌中的一种热稳定性肠毒素，是引起食源性腹泻的主要原因之一。前期研究表明，其编码基因astA广泛存在于致泻性大肠杆菌的质粒和染色体上并影响EAST1毒素的表达，且引起食物中毒菌株的astA基因具有多样性并在氨基酸残基上表现出更多的差异。然而多数研究因样本量小且菌株来源单一，导致astA基因的分型、致病性强弱以及与其在基因组中的位置关系尚不明确。本项目以食物、动物粪便及健康人和病人来源的272株含有astA基因的致泻性大肠杆菌为研究对象，与标准株和食物中毒菌株的astA基因序列和氨基酸序列进行对比分型，结果表明，71.32%（194株）菌株的astA基因型与标准型相同，15.44%（42株）菌株的astA基因型与食物中毒菌株的基因型相同，其中96-127-23(clone 2)型17株(6.25%)，96-127-23(clone 3)型1株(0.37%)，V199(clone 3)型24株(8.82%)，主要来源于牛粪和猪粪样品，结果与前期研究的猪源和牛源大肠杆菌致泻性强的结果相一致。该研究结果为后续大肠杆菌食物中毒的防控起到积极的参考价值。