USDA, ARS, National Animal Disease Center, Food Safety and Enteric Pathogens Research Unit, Ames, IA, 50010, USA.
Oak Ridge Institute for Science and Education (ORISE)/ARS Research Participation Program, Oak Ridge, TN 37831.
Vet Microbiol. 2018 Jun;219:190-199. doi: 10.1016/j.vetmic.2018.04.003. Epub 2018 Apr 20.
Escherichia coli O157:H7 (O157) can cause from a mild diarrheal illness to hemorrhagic colitis and hemolytic uremic syndrome in humans. Cattle are the primary reservoir for O157 and fecal shedding of O157 by these animals is a major risk factor in contamination of cattle hides and carcasses at slaughter. Vaccination is an important strategy to reduce fecal shedding of O157 in cattle. In this study, we evaluated the immunogenicity and efficacy of an inactivated vaccine strain of O157 formulated with an adjuvant. This vaccine strain was deleted of the hha gene enabling high level expression of the locus of enterocyte effacement (LEE) encoded proteins required for O157 colonization in cattle. The inactivated vaccine strain emulsified with the adjuvant or suspended in the phosphate-buffered saline (PBS) was injected in the neck muscles of two groups of weaned calves followed by a booster three weeks later with the corresponding formulation. Animals in groups 3 and 4 were injected similarly with the adjuvant and PBS, respectively. All animals were orally inoculated three weeks post-booster vaccination with a live culture of O157. The animals vaccinated with the adjuvanted vaccine showed higher serum antibody titers to the vaccine strain and shed O157 for a shorter duration and at lower numbers compared to the animals vaccinated with the non-adjuvanted vaccine, adjuvant-only, or PBS. Western blotting of the vaccine strain lysates showed higher immunoreactivity of serum IgG in vaccinated animals to several O157-specific proteins and lipopolysaccharides (LPS). The vaccination induced IgG showed specificity to LEE-encoded proteins and outer membrane LPS as LEE and waaL deletion mutants, unable to produce LEE proteins and synthesize high molecular weight LPS, respectively, yielded significantly lower antibody titers compared to the parent vaccine strain. The positive reactivity of the immune serum was also observed for purified LEE-encoded proteins EspA and EspB. In conclusion, the results of this animal study showed that a two-dose regimen of an adjuvanted vaccine is capable of inducing O157-specific immune response that directly or indirectly reduced fecal shedding of O157 in cattle.
大肠杆菌 O157:H7（O157）可引起人类轻度腹泻病、出血性结肠炎和溶血尿毒综合征。牛是 O157 的主要储存宿主，这些动物的粪便中 O157 的脱落是牛皮和屠体在屠宰时污染的主要危险因素。疫苗接种是减少牛粪便中 O157 脱落的重要策略。在这项研究中，我们评估了用佐剂配制的 O157 灭活疫苗株的免疫原性和功效。这种疫苗株缺失了 hha 基因，从而能够高水平表达 O157 在牛中定植所需的肠上皮细胞 effacement（LEE）编码蛋白的基因座。将佐剂乳化的灭活疫苗株或悬浮在磷酸盐缓冲盐水（PBS）中，注射到两组断奶小牛的颈部肌肉中，三周后用相应的制剂进行加强免疫。第 3 组和第 4 组的动物分别用佐剂和 PBS 进行类似注射。所有动物在加强免疫后三周口服接种 O157 活菌。用佐剂疫苗接种的动物显示出更高的针对疫苗株的血清抗体滴度，与用非佐剂疫苗、佐剂或 PBS 接种的动物相比，它们的 O157 脱落持续时间更短，数量更少。对疫苗株裂解物进行 Western blot 分析显示，接种动物的血清 IgG 对几种 O157 特异性蛋白和脂多糖（LPS）具有更高的免疫反应性。接种诱导的 IgG 特异性针对 LEE 编码蛋白和外膜 LPS，因为分别不能产生 LEE 蛋白和合成高分子量 LPS 的 LEE 和 waaL 缺失突变体，与亲本疫苗株相比，产生的抗体滴度显著降低。免疫血清对纯化的 LEE 编码蛋白 EspA 和 EspB 也表现出阳性反应。总之，这项动物研究的结果表明，两剂佐剂疫苗能够诱导 O157 特异性免疫反应，直接或间接减少牛粪便中 O157 的脱落。
