The outer membrane proteins of Stenotrophomonas maltophilia are potential vaccine candidates for channel catfish (Ictalurus punctatus)

• OMPs of S. maltophilia were prepared by using the sodium dodecyl sulfate (SDS) method.
• Biological characteristics of OMPs were analyzed by SDS-PAGE, and the OMPs contain more than 6 proteins from 78.3 to 14.2 kDa.
• OMPs of S. maltophilia as channel catfish potential vaccine against S. maltophilia.
• Pro, Fcps and Gly have been used to investigate the enhancement effect to OMPs of S. maltophilia, and their works were good.
• OMPs + Pro, OMPs + Fcps, OMPs + Gly and OMPs conferred RPS = 73.33, 66.67, 63.33 and 60%, respectively.

Channel catfish (Ictalurus punctatus) is an important agricultural fish that has been plagued by Stenotrophomonas maltophilia (S. maltophilia) infections in recent years, some of them severe. The outer membrane proteins (OMPs) of S. maltophilia are one of the most immunogenic and highly conserved candidates for vaccine development in aquaculture. The present study investigated OMPs of S. maltophilia as vaccine on immune response and disease resistance against S. maltophilia of channel catfish and investigated the enhancement effect of natural adjuvants Propolis (Pro), FIG polysaccharide (Fcps), Glycyrrhizine (Gly) to OMPs of S. maltophilia for further study. The results indicated that channel catfish injected intraperitoneally with OMPs showed better immune response including leukocytes phagocytosis activity, serum bactericidal activity, complement C3, IgM level and an increasement of resistance against S. maltophilia compared to the control group. Moreover, Pro, Fcps and Gly could enhance the immune response of OMPs. The relative percent of survival (RPS) was 73.33%, 66.67%, 63.33%, 60%, 0% in fish injected OMPs + Pro, OMPs + Fcps, OMPs + Gly, OMPs and 0.65% normal saline, respectively. These results suggested that OMPs used as vaccine could induce and stimulate immune response and enhance disease resistance in channel catfish, especially for Pro as immunoenhancer. Results revealed that OMPs were an effective vaccine against S. maltophilia in channel catfish.