The Research Of Pathogenetic Characteristics Of Enterotoxigenic Escherichia Coli And The Screening And Inhibitory Effect Of Probiotic On Pathogenic Bacteria

Enterotoxigenic Escherichia coli (ETEC) is one of the most important pathogenic bacteria in human and animals (postweaning piglets, calves, lambs). Neonatal animals often die from diarrhea and dehydration after infected ETEC. The diarrhea is responsible for economic losses due to mortality, morbidity, decreased growth rate, and cost of medication. At present, the effective way to treat this disease is to add antibiotics to the feed, but it is controversial and averse because of the problem of the bacteria with resistance to antibiotics. Many countries have forbidden or restricted the use of antibiotics and side-effect. Probiotic is frequently and successfully adopted to add to the feed because it is nontoxic, no resistance, no residue and no side-effect.This paper includes application for Green fluorescent protein (GFP) in the research of pathogenesis of ETEC and the screening and inhibitory effect of probiotic on pathogenic bacteria. The mainly results of the research are as follows:1. The plasmid pGLO with green fluorescent protein gene was transformed successfully to enterotoxigenic Escherichia coli strain K88 by electroshock. It could be observed that the GFP expressed stably and efficiently in transformant by the detection of ultraviolet radiating and fluorescent microscope. By detection of PCR amplification of a structural gene in flagellum, the analysis of fatty acid and serological identification,the transformant and the wild-type strains were proved to have the same genetic background. Meanwhile the transformant was not impaired in their ability to grow under different ferment conditions such as different temperature, pH and salt concentration of culture media, compared with the wild-type strain.2. The mice model was established by challenged K88 and K88-GFP. In the model, LD₅₀ (median lethal dose) of K88 was 5.53×10⁸ CFU/mL, LD₅₀ of K88-GFP was 4.86×10⁸ CFU/mL. Fluorescence provided a convenient way for the study of adherence and colonization in organs of mice. A large number of K88-GFP bacteria were discovered in liver and kidney, whereas only rare bacteria were obtained from on...