Brucella melitensis 16MΔTcfSR as a potential live vaccine allows for the differentiation between natural and vaccinated infection.

Brucellosis is a zoonotic disease that poses a serious threat to public health and safety. Although the live attenuated vaccines targeting brucellosis, such as M5-90, are effective, there are a number of drawbacks to their use. For example, the vaccines are unable to differentiate between the natural and vaccinated forms of the infection, and these vaccines have also been shown to cause abortion in pregnant animals. Therefore, a safer and more potent vaccine is required. In the present study, a B. melitensis 16M TcfSR promoter mutant (16MΔTcfSR) was constructed in an attempt to overcome these drawbacks. A TcfSR mutant was derived from B. melitensis 16M and tested for virulence and protection efficiency. Levels of immuoglobulin G (IgG), and cytokine production were determined. In addition, TcfS was assessed as a diagnostic marker for brucellosis. The survival capacity of the 16MΔTcfSR mutant was shown to be attenuated in the RAW 264.7 murine macrophage cell line and BALB/c mice, and the vaccination was shown to induce a high level of protective immunity in BALB/c mice. In addition, the 16MΔTcfSR vaccination elicited an anti-Brucella-specific IgG response and induced the secretion of interferon-γ. Thus, the TcfS antigen allowed for the serological differentiation between the natural and vaccinated infection in animals. In conclusion, the results demonstrated that the 16MΔTcfSR mutant was attenuated in murine macrophage cells and BALB/c mice; therefore, 16MΔTcfSR is a potential candidate for a live attenuated vaccine against B. melitensis infection.