Preliminary Study On Biological Function Of 43K OMP Gene Mutant Strains Of Fusobacterium Necrophorum

Fusobacterium necrophorum（F.necrophorum）is a gram-negative and anaerobic bacterium.It mainly causes ruminant foot rot,liver abscess and calf diphtheria with tissue necrotizing and suppurative lesions,and participates in the pathogenic process of dairy cow mastitis and endometritis.43K OMP is an important outer membrane proteins of F.necrophorum,which can mediate the adhesion of F.necrophorum to host cells.However,the biological functions of 43K OMP other than adhesion to host cells have not been fully revealed.In order to study the biological function of 43K OMP gene in F.necrophorum infection,the biological characteristics of 43K OMP gene deletion strain were studies by the following methods.In order to clarify the effect of defective 43K OMP gene on the biological characteristics of F.necrophorum,this study compared the bacterial morphology,colony morphology,growth curve,drug resistance,biofilm content and morphology,cell adhesion ability,inhibition of cell proliferation ability,induction of apoptosis ability and mouse virulence of A25 and A25Δ43K OMP.The results showed that there was no significant difference in bacterial morphology,colony morphology,growth curve and inhibition of RAW264.7 cell proliferation between A25 and A25Δ43K OMP;The drug sensitivity of A25Δ43K OMP to clarithromycin,kanamycin and polymyxin B increased,the drug sensitivity to ampicillin,erythromycin and sulfamethoxazole decreased,the content of biofilm increased significantly（P<0.05）,and aggregated colonies and gully structures were formed earlier;The adhesion ability of A25Δ43K OMP to Eph4 1424 cells,AML-12 cells,BEND cells and MAC-T cells decreased significantly（P<0.05）,and the apoptosis ability of RAW264.7 cells induced by infection for 4 h decreased significantly（P<0.05）;In vivo tests showed that the mortality of mice in A25 group was 100%,the time of death of mice was concentrated in 1～3 d after infection,and there was no obvious pathological change in the eyes of dead mice.The mortality of mice in A25Δ43K OMP was 80%,the time of death of mice was concentrated in 5～7 d,and white coagulative necrosis appeared in the eyes of dead mice（6/10）.The LD₅₀ of A25 and A25Δ43K OMP were 3.66×10⁷CFU and9.44×10⁷CFU respectively.Compared with A25,the virulence of A25Δ43K OMP decreased by about 3 times.In conclusion,the 43K OMP gene of F.necrophorum can participate in the adhesion process of F.necrophorum to host cells,play an important role in the drug resistance and biofilm formation of F.necrophorum,and is related to the virulence of F.necrohphorum.This study provides a theoretical basis for the related research of F.necrophorum 43K OMP.