耐药大肠杆菌的致病性与免疫原性

目的了解大肠杆菌耐药株的致病性与免疫原性。方法临床分离耐药大肠杆菌,经适宜条件培养后接种小鼠,观察耐药菌株对小鼠的致病性;并选择已知血清型的不同耐药谱和不同耐药水平的菌,分别培养至对数生长期,经甲醛灭活后免疫小鼠,2周后分别用致死剂量的原菌株和同期分离菌株进行攻毒,考察耐药菌株免疫原性。结果24株耐药菌普通肉汤培养物分别感染小鼠,在接种后18h,存活率仅为4%。只有2株菌在1周内仍不能将小鼠全部致死,经小鼠体内传3代后,可在18h内致死小鼠。耐药谱广的菌株感染的小鼠,心肌发生颗粒变性、局灶性出血、坏死;肝脏糖元溶解,脂肪变性;脾脏轻度淤血,淋巴细胞减少;肾脏出血,肾小球肾炎,上皮细胞颗粒变性,水泡变性。而耐药种类少的菌株与对照敏感菌株感染的小鼠主要特征为脾脏出血、淤血,坏死,脾小体消失;肠上皮细胞坏死、脱落、卡他性肠炎。免疫小鼠以免疫用菌株攻毒,均可得较高的保护率,最低为75%,最高为100%。免疫小鼠用非免疫菌株攻毒,小鼠感染后症状出现较缓慢,在18h后出现死亡高峰。耐药种类少的菌株免疫小鼠,对同期分离的非免疫用的致病性大肠杆菌攻击的保护率偏低,而对受试的11种抗生素耐受7种以上的菌株免疫小鼠后,对致病大肠杆菌攻击的保护率显著提高,多数达到75%以上,经统计学分析差异显著。结论耐药大肠杆菌具有较强致病性,且耐药特性与其免疫保护效果相关,多重耐药株对当前流行菌株具有更好的免疫保护作用。

Pathogenicity and Immunogenicity of Drug-resistant E. coli

Objective To explore the pathogenicity and immunogenicity of drug-resistant E.coli.Methods The clinically isolated drug-resistant E.coli strains were cultured under suitable condition and tested for pathogenicity in mice.The E.coli strains of known serotypes and different drug resistance spectrums and levels were cultured until logarithmic growth phase,then inactivated with foraldehyde and immunized to mice respectively.The immunized mice were challenged with a lethal dose of original strain or the strain isolated homochronously with the original one 2 weeks later,and the survival rates of mice were observed.Results The survival rate of mice 18 h after inoculation with 24 drug-resistant E.coli strains cultured in common broth medium was only 4%.The mice inoculated with another 2 strains died partially within 1 week.However,after subculture for 3 passages in mice,the 2 strains caused the death of mice within 18 h.In the mice inoculated with broad spectrum drug resistance,granular degeneration,focal hemorrhage and necrosis in cardiac muscle,glycogen dissolution and fatty degeneration in liver,mild haemostasis and decreased number of lymphocyte in spleen,as well as hemorrhage in kidney,glomerulonephritis,granular and hydatidiform degenerations of epithelial cells,were observed.However,in the mice inoculated with strains resistant to only a few of drugs or the drug-sensitive strains as control,the hemorrhage,haemostasis,necrosis and disappearance of globule in spleen,necrosis and abscission of entreic eptithelium cells as well as catarrhal enteritis were observed.The protective rate of mice challenged with original strain was 75% to 100%.The death peak of immunized mice appeared 18 h after challenge with the strains isolated homochronously with the original strain,and,compared with that in unimmunized mice,the post-infection symptoms appeared slowly in immunized mice.After challenge with the strains isolated homochronously with the original strain,the protective rate of mice immunized with the strains resistant to only a few of drugs was low,however,the protective rate of mice immunized with broad spectrum drug-resistant strains was significantly high.Conclusion The drug-resistant E.coli strains showed high pathogenicity,and their drug-resistance was associated with immune protective effect.Broad spectrum drug-resistant strain showed good immune protective effect against the challenge with the current strain.