School of Veterinary Medicine and Biomedical Sciences, University of Nebraska-Lincoln, Lincoln, NE 68583-0905, USA.
Vet Microbiol. 2013 Jan 25;161(3-4):315-24. doi: 10.1016/j.vetmic.2012.07.048. Epub 2012 Aug 3.
Heat-labile enterotoxin (LT) produced by enterotoxigenic Escherichia coli (ETEC) increases bacterial adherence to porcine enterocytes in vitro and enhances small intestinal colonization in swine. Heat-stable enterotoxin-b (STb) is not known to affect colonization; however, through an induction of net fluid accumulation it might reduce bacterial adherence. The relationship between fluid accumulation and bacterial adherence in jejunal loops inoculated with ETEC strains that produce LT, STb, both, or neither toxin was studied. Ligated jejunal loops were constructed in weaned Yorkshire pigs in two independent experiments (Exp. 1, n=5, 8-week-old; Exp. 2, n=6, 6-8-week-old). Each pig was inoculated with six F4ac(+)E. coli strains: (1) LT(+), STb(+) parent (WAM2317); (2) STb(-) (ΔestB) mutant (MUN297); (3) MUN297 complemented with STb (MUN298); (4) LT(-) STb(-) (ΔeltAB ΔestB) mutant (MUN300); (5) MUN300 complemented with LT (MUN301); and (6) 1836-2 (non-enterotoxigenic, wild-type). Pigs were confirmed to be K88 (F4)ab/ac receptor-positive in Exp. 2 by testing for intestinal mucin-type glycoproteins and inferred to be receptor-positive in both Exp. 1 and 2 based on histopathologic evidence of bacterial adherence. Strains that produced STb induced marked fluid accumulation with the response (ml/cm) to WAM2317 and MUN298 significantly greater than that to the other strains (P<0.0001). Conversely, bacterial adherence scores based on immunohistochemistry and CFU/g of washed mucosa were both lowest in the strains that expressed STb and highest in those that did not. For the two experiments combined, the Pearson correlation coefficient (R) between fluid volume (ml/cm) and log CFU per gram was -0.57021 (P<0.0001); R(2)=0.3521 (n=197). These results support the hypothesis that enterotoxin-induced fluid accumulation flushes progeny organisms into the lumen of the bowel, thereby increasing the likelihood of fecal shedding and transmission of the pathogen to new hosts.
不耐热肠毒素（LT）由肠产毒性大肠杆菌（ETEC）产生，可增加细菌在体外对猪肠细胞的黏附，并增强猪小肠的定植。热稳定肠毒素-b（STb）据知不会影响定植；然而，它可能通过诱导净液体积累来减少细菌黏附。本研究旨在研究产生 LT、STb、两者或均不产生毒素的 ETEC 菌株接种后的空肠袢中液体积累与细菌黏附之间的关系。在两个独立的实验（实验 1，n=5，8 周龄；实验 2，n=6，6-8 周龄）中，在断奶约克夏猪中构建结扎空肠袢。每只猪接种 6 株 F4ac(+)大肠杆菌菌株：（1）LT(+)、STb(+)亲本（WAM2317）；（2）STb(-)（ΔestB）突变株（MUN297）；（3）用 STb 互补的 MUN297（MUN298）；（4）LT(-)、STb(-)（ΔeltAB ΔestB）突变株（MUN300）；（5）用 LT 互补的 MUN300（MUN301）；（6）1836-2（非肠产毒型，野生型）。通过检测肠粘蛋白型糖蛋白，实验 2 中猪被证实为 K88（F4）ab/ac 受体阳性，根据细菌黏附的组织病理学证据，推断实验 1 和 2 中的猪均为受体阳性。产生 STb 的菌株引起显著的液体积累，WAM2317 和 MUN298 的反应（ml/cm）显著大于其他菌株（P<0.0001）。相反，基于免疫组化和洗去黏膜的 CFU/g 的细菌黏附评分在表达 STb 的菌株中最低，而在不表达 STb 的菌株中最高。对于两个实验的综合分析，体积（ml/cm）和每克 CFU 的对数之间的 Pearson 相关系数（R）为-0.57021（P<0.0001）；R2=0.3521（n=197）。这些结果支持这样的假设，即肠毒素诱导的液体积累将后代生物体冲洗到肠腔中，从而增加粪便脱落和病原体传播给新宿主的可能性。
