Kairong Mao

Brucellosis is a widespread zoonotic disease caused by Gram-negative Brucella bacteria. Immunisation with attenuated vaccine is an effective method of prevention, but it can interfere with diagnosis. Live, attenuated Brucella abortus strain 104M has been used for the prevention of human brucellosis in China since 1965. However, at present, no fast and reliable method exists that can distinguish this strain from field strains. Single nucleotide polymorphism (SNP)-based assays offer a new approach for such discrimination. SNP-based minor groove binder (MGB) and Cycleave assays have been used for rapid identification of four Brucella vaccine strains (B. abortus strains S19, A19 and RB51, and B. melitensis Rev1). The main objective of this study was to develop a PCR assay for rapid and specific detection of strain 104M. We developed a SNP-based MGB PCR assay that could successfully distinguish strain 104M from 18 representative strains of Brucella (B. abortus biovars 1, 2, 3, 4, 5, 6, 7 and 9, B. melitensis biovars 1, 2 and 3, B. suis biovars 1, 2, 3 and 4, B. canis, B. neotomae, and B. ovis), four Brucella vaccine strains (A19, S19, S2, M5), and 55 Brucella clinical field strains. The assay gave a negative reaction with four non-Brucella species (Escherichia coli, Pasteurella multocida, Streptococcus suis and Pseudomonas aeruginosa). The minimum sensitivity of the assay, evaluated using 10-fold dilutions of chromosomal DNA, was 220 fg for the 104M strain and 76 fg for the single non-104M Brucella strain tested (B. abortus A19). The assay was also reproducible (intra- and inter-assay coefficients of variation = 0.006–0.022 and 0.012–0.044, respectively). A SNP-based MGB PCR assay was developed that could straightforwardly and unambiguously distinguish B. abortus vaccine strain 104M from non-104M Brucella strains. Compared to the classical isolation and identification approaches of bacteriology, this real-time PCR assay has substantial advantages in terms of simplicity and speed, and also reduces potential exposure to live Brucella. The assay developed is therefore a simple, rapid, sensitive, and specific tool for brucellosis diagnosis and control.

To study the pattern recognition and activation effect of mast cells infected by Brucella (B.) suis S2. Mast cells derived from bone marrow in vitro were infected by B.suis S2. The change in the cell morphology was observed with Wrights-Giemsa's staining, and cell degranulation was tested with toluidine blue staining. The extracellular levels of histamine, IFN-γ and IL-12 of mast cells at 1 and 12 h after infection were detected by indirect ELISA. The uptake pattern of mast cells to B.suis S2 was determined by laser-scanning confocal microscopy. The expressions of TLR4 and TLR8 mRNA were detected by RT-PCR at 12 and 24 h after infection by B.suis S2, and the TLR4 and TLR8 protein expressions were detected by flow cytometry at 24 h. The form of mast cells infected by B.suis S2 was obviously changed. Significant degranulation was observed at 1 h, and at 1, 12 h post-infection by B.suis S2, the content of histamine secreted by mast cells was significantly higher than that of normal control group (P<0.05), and IFN-γ and IL-12 were not found. At 30 min and 1 h, B.suis S2 bound to the mast cell surface and were not uptaken into the mast cells. Compared with the control group, the expression of TLR4 mRNA increased after 12 h infection by B.suis S2, and was reduced at 24 h. The expression of TLR4 protein rose at 24 h, but the expression of TLR8 mRNA and protein did not alter at 12 and 24 h after infection by B.suis S2. B.suis S2 can bind to the cell surface and activate mast cells, cause their degranulation, induce the release of histamine, but IFN-γ and IL-12 were not found during the observing time. The mechanism may be that B.suis S2 can be recognized by mast cells through TLR4 but can not be phagocytosed by mast cells.

Objective To make a comparison of the characteristics between macrophages and dendritic cells (DC) infected by Brucella suis (B. suis) S(2);. Methods Wrights-Giemsa's stainning was used to observe the cell morphology and calculate the phagocytic rate. ELISA was employed to detect the expressions of IL-12 and TNF-α in cell culture supernatants as well as the contents of IFN-γ and IL-4 in the co-culture with T cells. With annexin-V-FITC/PI double staining, the cell apoptosis rate was determined by flow cytometry. Results 1 h after infected by B. suis S(2);, the phagocytic rate of macrophages was (43.6±4.8)%, which was significantly higher than that of the DC (16.3±2.7)% (P<0.05). The apoptosis rates of normal macrophages and macrophages 6, 12 and 24 h after infected by B. suis S(2); were (3.09±1.21)%, (19.89±1.36)%, (22.73±2.21)% and (42.44±3.12)%, respectively, which were dramatically higher than those of the DC at the corresponding time points, being (1.82±0.01)%, (3.76±0.13)%, (7.87±0.56)% and (9.08±0.23)%, respectively (P<0.05). The levels of IL-12 secreted by macrophages 24 and 48 h after infected by B. suis S(2); were significantly lower than those by the DC (P<0.01). At 24, 48 and 72 h, the levels of TNF-α secreted by macrophages were dramatically lower than those by the DC (P<0.01), and the levels of IFN-γ in the co-culture supernatants of macrophages and T cells were significantly lower than those in DC and T cell co-culture (P<0.01). Conclusion Macrophages have a better ability in phagocytosing B. suis S(2); than DC and the apoptosis rate of macrophages is higher than that of DC after infected by B. suis S(2);, but in activating and inducing the cellular immune response and presenting antigen, DC are stronger than macrophages.

Brucella melitensis and Brucella suis are intracellular pathogens of livestock and humans. Here we report four genome sequences, those of the virulent strain B. melitensis M28-12 and vaccine strains B. melitensis M5 and M111 and B. suis S2, which show different virulences and pathogenicities, which will help to design a more effective brucellosis vaccine.

Vaccination has not been used widely because of the interference in the discrimination between infected and vaccinated animals in immune-screening procedures. In the present study, chloramphenicol resistance gene (Cm(r)) was cloned into the genomic DNA of brucella suis S2 strain by homologous recombination with knocking out the WbkC gene, and obtained the recombinant rS2-WbkC. Further study confirmed that rS2-WbkC was conversed into rough-phenotype form smooth-phenotype. The recombinant keeps the ability to chloramphenicol resistance after 25 passages in tryptic soy agar (TSA). Mice tests showed rS2-WbkC offered similar protection to S2 strain, but more safe than S2. Serum collected form rS2-WbkC immunized mice could be easily distinguished from antiserum produced by smooth-phenotype brucella abortus. In view of these result, rS2-WbkC is a promising candidate for vaccine strain.

Brucellosis is a crucial zoonosis caused by Brucella, which has some traits of wide hosts, great infectivity and difficulty in cure. Brucellosis caused great losses to farming and people's health. Vaccination is the main measure used to control Brucellosis, and some attenuated Brucella strains were often used as vaccines. To find more effective vaccines, Scientists are now constructing recombinant strains, DNA vaccines and subunit vaccines, as well as inducing new attenuated strains from isolations. The present applications of B. abortus strain 19 (S19) , B. melitensis Rev. 1 (Rev. 1), B. suis strain 2 (S2), B. abortus strain 45/20 (45/20) and rough strain B. abortus 51 (RB51) were discussed. And some recent research work on Brucella vaccines, such as Brucella recombinant vaccines, DNA vaccines and so on, were reviewed in this paper.