猪源大肠杆菌(ETEC、STEC、AEEC)毒力基因及其与O抗原型的关系

目的]揭示从我国部分地区仔猪腹泻或水肿病病猪体内分离到的300个大肠杆菌分离株所属病原型(pathotype)、毒力基因及其与O血清型的关系.方法]O血清型采用常规的凝集试验进行测定,毒力基因采用PCR方法检测.结果]通过对这300个分离株的O血清型及其毒素、紧密素和黏附素基因进行鉴定,结果显示除50株未定型、17株自凝外,测定出233个分离株的血清型,这些分离株覆盖了45个血清型,其中以0149、0107、0139、093和091为主,共133株,占定型菌株的57.1%;拥有est Ⅰ、estⅡ、elt、stx2e和eae A基因的菌株分别为102(34.0%)、190(63.3%)、81(27.0%)、57(19.0%)和54(18.0%)株;分离株中有51株K88基因阳性(其中菌毛表达率为100%),75株F18基因阳性(其中菌毛表达率为50.7%),在K88菌株中,0149血清型与est Ⅰ或estⅡ elt密切相关,在F18菌株中,0107血清型与est Ⅰ或estⅡ、0139血清型与stx2e紧密相关.依其毒力特征可将这些分离株分为以下6种类型:ETEC、STEC、AEEC、ETEC/STEC、AEEC/ETEC和AEEC/ETEC/STEC,分别拥有190、24、36、32、17和1个菌株,占分离株的63.3%、8.0%、12.0%、10.7%、5.7%和0.3%.通过分析这些分离株的O血清型、毒素类型和黏附素型之间的相关性:猪源ETEC以0149、0107、093和098等血清型为主,0149:K88菌株主要与estⅡ或estⅡ elt肠毒素相关,0107:F18菌株主要与estⅡ相关,093和098血清型菌株主要与estⅡ肠毒素相关;STEC菌株以0139:F18血清型为主,拥有stx2e;AEEC菌株拥有紧密素,无明显优势血清型;ETEC/STEC菌株以0107:F18和0116:F18血清型为主,主要与est Ⅰ stx2e或estⅡ stx2e密切相关,ETEC/AEEC菌株以091和0107血清型为主,全部拥有肠毒素est Ⅰ和紧密素基因.结论]我国至少存在6种病原型的猪肠道致病性大肠杆菌,其中ETEC为我国部分地区猪大肠杆菌病的主要病原,同时其病原型日益复杂.

Virulence genes of pathogenic Escherichia coli from ill pigs in China and their relationship with O-serogroups

OBJECTIVE: We determined the distribution of serogroups and virulence factors among Escherichia coli isolates from pigs with diarrhea and/or edema disease from 10 provinces in China between 1998 and 2007. METHODS: Three hundred E. coli isolates were serogrouped with O-antisera and detected for genes of enterotoxins, shiga-toxin-two-variant (Stx2e), intimin, K88, K99, 987P, F18 and F41 fimbrial antigens by PCR. RESULTS: Among 300 isolates, 233 were determined to be placed in serogroups, 50 were unable to be serogrouped, and the rest 17 auto-agglutinated. These isolates distributed in 45 serogroups and 57.1% (133/233) belonged to 5 O serogroups: O149, O107, O139, O93 and O91. Several uncommon O serogroups were discovered. PCR analysis confirmed the genes of est I (STa), est II (STb), elt (LT), stx2e (Stx2e) and eaeA (Intimin) within the isolates. There were six pathotypes of porcine E. coli by their pathogenic factors, namely enterotoxigenic E. coli (ETEC), shiga toxin-producing E. coli (STEC), attaching-effacing E. coli (AEEC), ETEC/ STEC, AEEC/ETEC and AEEC/ETEC/STEC. The correlation between pathotypes and serogroups showed that the combinations of O149/K88/estII, O149/K88/est II+elt, O107/F18/est II, 093/est II and O98/est II were common types in ETEC strains, O139/ F18/stx2e for STEC strains, eaeA gene for AEEC strains, O107/F18/estI+stx2e, O107/F18/estII + stx2e and O116/F18/est I +elt+stx2e for ETEC/STEC strains, 091/est I/eaeA and O107/est I /eaeA for AEEC/ETEC/STEC strains". CONCLUSION: ETEC was commonly associated with swine colibacillosis, whereas the kinds of enteric E. coli pathogens become more complex in China.