Short communication: Bacillus subtilis expressing chicken NK-2 peptide enhances the efficacy of EF-1a vaccination in Eimeria maxima-challenged broiler chickens

Authors: LEE, YOUNGSUB - US Department Of Agriculture (USDA); Park, Inkyung; WICKRAMASURIYA, SAMIRU - US Department Of Agriculture (USDA); Lillehoj, Hyun

Submitted to: Animals
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/15/2023
Publication Date: 4/18/2023
Citation: Lee, Y., Park, I.N., Wickramasuriya, S.S., Lillehoj, H.S. 2023. Short communication: Bacillus subtilis expressing chicken NK-2 peptide enhances the efficacy of EF-1a vaccination in Eimeria maxima-challenged broiler chickens. Animals. https://doi.org/10.3390/ani13081383.
DOI: https://doi.org/10.3390/ani13081383

Interpretive Summary: Avian coccidiosis is caused by intestinal parasites costing more than $ 13 billion annual losses to the global poultry industry due to inefficient feed utilization, impaired growth rate, and high mortality following parasite-induced intestinal damage. Due to the restriction of using antibiotics in poultry production, there has been increasing interest in developing antibiotic-alternative strategies to manage coccidiosis. In this report, ARS scientists describe a novel antibiotic-alternative strategy which involves recombinant vaccination strategy using immunodominant antigens of Eimeria to elicit a protective immune response in the gut. Using an immunodominant antigen, elongation factor-1a (EF-1a), this study showed that EF-1a recombinant vaccination elicits cross-protective immunity against many different species of Eimeria parasites. Furthermore, this study showed that EF-1a-induced protective immunity can further be enhanced by co-administration with a chicken antimicrobial peptide, NK-lysin 2 (cNK-2). Therefore, this novel strategy can be used to enhance host protection, immune response, and resilience against avian coccidiosis.

Technical Abstract: This study was conducted to investigate synergistic effects of orally delivered Bacillus subtilis (B. subtilis) expressing chicken NK-2 peptide (cNK-2) on vaccination with recombinant Eimeria elongation factor-1a (rEF-1a) protein against Eimeria maxima (E. maxima) infection in broiler chickens. One-day-old chickens were assigned into the following five groups: control (CON, no Eimeria infection), non-immunized control (NC, PBS), component 1 (COM1, rEF-1a only), component 2 (COM2, rEF-1a plus B. subtilis empty vector), and component 3 (COM3, rEF-1a plus B. subtilis-NK-2). The first immunization was administered intramuscularly on day 4, and the second immunization was given one week later with the same concentration of components as the primary immunization. The immunization of B. subtilis spores (COM2 and COM3) were performed by oral administration given for 5 consecutive days a week later the second immunization. On day 19, all chickens except the CON group were orally challenged with sporulated E. maxima oocysts (1.0 × 104/chicken). The results of the in vivo vaccination showed that all chickens immunized with rEF-1a (COM1, COM2, and COM3) produced higher (p < 0.05) serum antibodies against EF-1a on 12 days post E. maxima infection (dpi). The COM3 group showed a significantly (p < 0.05) higher average body weight gain (BWG) on 0-6, 6-9, and 0-12 dpi compared to those of non-immunized chickens (NC). Immunization with rEF-1a alone (COM1) reduced gut lesion score on 6 dpi and fecal oocyst shedding on 9 dpi, whereas co-administration with B. subtilis spores (COM2 or COM3) led to further reduction in lesion score. E. maxima infection increased the expression levels of IFN-' and IL-17ß in the jejunum, but these expressions were downregulated in the rEF-1a-immunized (COM1) group and in the groups immunized with rEF-1a and orally treated with B. subtilis spores (COM2 or COM3) at 4 dpi. A reduced gene expression of occludin in the jejunum of E. maxima-infected chickens on 4dpi was upregulated following immunization with COM2. Collectively, rEF-1a vaccination induced significant protection against E. maxima infection in broiler chickens, and the efficacy of rEF-1a vaccination was further enhanced by co-administration with orally-delivered B. subtilis spores expressing chicken antimicrobial peptide, cNK-2.