Immunogenic Potency of Formalin and Heat Inactivated E. coli O157:H7 in Mouse Model Administered by Different Routes

Abstract

Background: Enterohemorrhagic Escherichia coli (E. coli) (EHEC) O157:H7 is a major foodborne pathogen causing severe disease in humans worldwide. Cattle are important reservoirs of E. coli O157:H7 and developing a specific immunity in animals would be invaluable. The administration of Whole Cell Vaccines (WCV) is a well-established method of vaccination against bacterial infections. Route of administration, inactivation and using suitable adjuvant have significant effects on the characteristics and efficacy of WCV.

Methods: In the present study, an attempt was made to evaluate the immunogenic potency of heat and formalin inactivated cells administered orally and subcutaneously in mouse model by ELISA. Mice pretreated with streptomycin were used as a model to evaluate the efficacy of subcutaneous versus oral administration of the vaccine. Following immunization, mice were infected with E. coli O157:H7 and feces were monitored for shedding.

Results: Both forms of inactivated cells induced immune response and hence protection against infectious diseases caused by E. coli O157:H7. However, formalin inactivated cells of E. coli O157:H7 showed superior antigenicity compared to heat inactivated cells. Subcutaneous immunization of mice with both heat and formalin inactivated E. coli O157:H7 induced significant specific levels of IgG antibodies but did not lead to significant antigen-specific IgA rise in feces, whereas oral immunization elicited significant levels of IgG antibodies with some animals developing antigen-specific IgA in feces.

Conclusion: Inactivated E. coli O157:H7 is highly immunogenic and can induce protective immune responses via oral immunization.

Keywords: Escherichia coli O157:H7; Formaldehyde; Hot temperature; Immunization; Mice; Vaccines.

Figure 1.

Agarose gel electrophoresis of PCR product of E. coli O157:H7 in order to confirm the bacteria. Lane 1: negative control; lane 2,4: positive control; lane 3: other bacteria; lane 5: 100 bp DNA ladder; lane 6–15: PCR product of the rfbE gene of E. coli O157:H7 grown in SMA.

Figure 2.

Specific serum IgG following oral versus subcutaneous immunization with inactivated bacteria. There were significant differences in antibody titer between immunized and control mice groups (p<0.05). A) IgG titer in the whole cell recipient group immunized subcutaneously, B) IgG titer in the whole cell recipient group immunized orally (Data represents the mean value±standard error of the three readings).

Figure 3.

E .coli O157:H7 specific serum and fecal IgA following oral immunization (A) Serum IgA titer whole cell and (B) Fecal IgA titer whole cell in different mice groups 7 days after the final immunization (Data represents the mean value±standard error of the three readings).

Figure 4.

E. coli O157:H7 shedding in feces following subcutaneous (A) and oral (B) administration in mice. Immunized and nonimmunized mice were orally fed with 10¹⁰ E. coli O157:H7 and shedding was monitored in the feces for 21 days. Differences were considered significant whenever p<0.05. The limit of detection for plating was 10¹⁰ CFU/0.1 g feces. XY graphs are used for presenting data.