Immunogenicity of a novel HMT13 adjuvant-based inactivated vaccine against Avian pathogenic Escherichia coli serogroups O36, O78, and O109.

Avian colibacillosis, mainly caused by avian pathogenic Escherichia coli (APEC), is one of the most prominent diseases in the poultry industry. Inactivated vaccines are crucial for preventing and controlling APEC infection, with adjuvants playing a key role in ensuring their effectiveness. However, traditional oil-emulsion inactivated vaccines often cause severe adverse reactions in animals. Based on the serogroups of 343 clinically isolated APEC strains from many provinces of China, O36, O78 and O109 were identified as the predominant serogroups currently circulating in these regions, with O36 and O109 being rarely noticed before. Consequently, we further screened these three dominant serogroups for their promising immunogenicity to develop effective inactivated vaccines. The immune side effects of 7 adjuvants including water-in-oil emulsions (Marc-52, ISA 71 VG, and ISA 78 VG), water-in-oil-in-water emulsions (ADJ 501 and HMT 13), oil-in-water emulsion (ADJ 2052), and aluminum hydroxide gels were evaluated and compared. The results showed that the vaccine formulated with HMT 13 as an adjuvant exhibited sufficient protective efficacy against homotypic APEC infection while effectively stimulating humoral and cellular immune responses. Moreover, inactivated vaccines containing HMT 13 could be easily absorbed at the inoculation site without interfering with chicken growth; they also possessed favorable emulsification properties facilitating storage. Therefore, HMT 13 represents an excellent adjuvant for developing an inactivated vaccine against chicken colibacillosis. This study presents a novel multivalent inactivated vaccine against chicken colibacillosis based on the use of HMT13 as an adjuvant, which offers a new approach for the prevention and control of APEC currently prevalent in most of China.