Date Published: July 19, 2017
Publisher: Springer Berlin Heidelberg
Author(s): Xiao Wang, Da Teng, Qingfeng Guan, Ruoyu Mao, Ya Hao, Xiumin Wang, Junhu Yao, Jianhua Wang.
Diarrhea caused by pathogenic Escherichia coli (E. coli) is one of the most serious infectious diseases in humans and animals. Due to antibiotics resistance and the lack of efficient vaccine, more attention should be paid to find potential versatile vaccine candidates to prevent diseases. In this study, the sequence homology analysis indicated that OmpF from E. coli CVCC 1515 shares a high identity (90−100%) with about half of the E. coli (46.7%) and Shigella (52.8%) strains. Then the recombinant OmpF was supposed to be developed as a versatile vaccine to prevent E. coli infection. OmpF was expressed in E. coli BL21 (DE3) using the auto-induction method. The recombinant OmpF (rOmpF) protein had an average molecular weight of 40 kDa with the purity of 90%. Immunological analysis indicated that the titers of anti-rOmpF sera against rOmpF and whole cells were 1:240,000 and 1:27,000, respectively. The opsonophagocytosis result showed that 72.21 ± 11.39 and 11.04 ± 3.90% of bacteria were killed in the rOmpF immunization and control groups, respectively. The survival ratio of mice immunized with rOmpF ranged between 40 and 60% as observed within 36 h after challenge, indicating mice were partially protected from E. coli CVCC 1515 infection. The expressed rOmpF protein induced an effective immune response, but only provide a weak protection against pathogenic E. coli CVCC 1515 and a small reduction in E. coli CICC 21530 (O157:H7) excretion in a mouse infection model. Native forms of the OmpF antigen may be studied for immunogenicity and potential protective efficacy.
Bacterial diarrhea caused by enterotoxigenic Escherichia coli is the main infectious disease in humans and animals worldwide (Johnson et al. 2010). Enterotoxigenic E. coli is transmitted by food or water contaminated with animal or human feces. The E. coli CVCC 1515 (O149:K91 and K88ac) strain, a predominant serotype, occurred more frequently in neonatal and postweaning pigs (Noamani et al. 2003; Maynard et al. 2003). Urease-positive E. coli CVCC 1515 was responsible for over 90% of cases of post-weaning diarrhea in recent outbreaks in Canada, which leading to substantial economic losses (Noamani et al. 2003). None of the attempted solutions to the problem of post-weaning diarrhea due to enterotoxigenic E. coli in pigs has been consistently effective. Another enteric pathogen E. coli CICC 21530 (O157:H7) strain is major cause of food-borne diarrheal disease, and can produce large quantities of one or more related potent toxins that cause severe damage to the lining of the intestine. Close to 75,000 cases of E. coli O157:H7 infection with 2–10% deaths are now estimated to occur annually in the United States (Perna et al. 2001; Vali et al. 2004). Although antibiotics and vaccines are currently available to prevent E. coli-induced diarrheas, antibiotics residues may pose severe health hazards in human and there are few available vaccines against homologous E. coli challenge. Therefore, more attention should be paid to find potential versatile vaccine candidates to prevent diseases induced by E. coli.
Considering the diversity of pathogenic E. coli serotype, we took more attention on developing a versatile vaccine that provides heterologous protection for E. coli, even other gram-negative pathogens such as Salmonella or Shigella. Lots of diarrheal illness were co-infected by these strains (O’Ryan et al. 2015). As we all known, porins exist most frequently as trimers and the sequence homology among porins of several genera such as Escherichia and Neisseria has shown a highly conserved nature (Yadav et al. 2014). Therefore, as a porin of E. coli, the OmpF protein was selected to be a candidate vaccine in our study.