Influences of Brucella melitensis with different virulence on macrophages

Abstract

Objective The survival and replication of two Brucella melitensis (B.melitensis) with different virulence in Raw 264.7 cell and their ability of inducing cytokine were compared to provide basis for establishing a method to identify virulence of Brucella. Methods B.melitensis 16M and M5 were used to infect Raw 264.7 cells and the amount of interleukin (IL)-1β, IL-6 and IL-12 in culture supernatants were detected via enzyme-linked immunosorbent assay at 4, 8 and 24 h after infection. We also evaluated the presence of colony-forming units (CFU) at 2, 4, 8, 24 and 48 h after infection via plate count method. Results The secretion of IL-6 in 16M and M5 groups at 4 h [(41.896 ± 0.575), (38.561 ± 0.305) ng/L] and 8 h [(38.943 ± 0.097), (38.159 ± 0.236) ng/L] after infection were higher than those of the control [(35.375 ± 1.132), (35.907 ± 1.025) ng/L, all P 0.05). A similar numbers of 16M and M5 were internalized while much more M5 organisms were killed within 8 hours after uptaken. Survived 16M exhibited a higher ability of replication than M5 in Raw 264.7 cells. Conclusion The intracellular viability of 16M is stronger than that of M5 and it indicates that the surviving and replication ability detection of Brucella in macrophages could be a feasible method to identify the virulence of different Brucella strains. Key words: Brucella; Virulence; Microphages; Cytokines