Molecular epidemiology of Burkholderia mallei isolates from India (2015-2016): New SNP markers for strain tracing

Glanders, caused by a bacterium called B. mallei, is primarily an infectious horse and human disease. Although its incidence is rare in developed countries, it is nonetheless prevalent in several geographical areas of the world. There is a lack of cost-effective, rapid and specific molecular typing tools for epidemiological tracing of glanders cases. We previously reported an SNP-based typing method that categorizes global B. mallei strains into three lineages (L1 to L3), as well as additional branches, sub-branches and groups. However, further discrimination of the Indian and Pakistani isolates within the L2B2sB2 sub-branch was not possible due to the lack of sufficient epidemiological markers. In this study, 10 B. mallei strains isolated from four states in India during 2015-2016 were whole genome sequenced; SNP analysis further confirmed their position in the L2B2sB2 branch. To better track the strains, four new markers targeting Indian or Pakistani strains, and specifically targeting sub-groups within the Indian strains, were identified. The new SNP markers were tested and validated on the 10 Indian isolates included in this study as well as on 6 contemporary B. mallei Pakistani strains. These rapid and discriminating typing tools will contribute to the epidemiological monitoring of B. mallei infections, particularly in South Asia and the Middle East, endemic regions of the disease.

Development of a microsphere-based immunoassay for the serological detection of glanders in equids

Burkholderia mallei is the etiologic agent of glanders, an infectious disease of solipeds, with renewed scientific interest due to its increasing incidence in different parts of the world. More rapid, sensitive and specific assays are required by laboratories for confirmatory testing of this disease. A microsphere-based immunoassay consisting of beads coated with B. mallei recombinant proteins (BimA, GroEL, Hcp1, and TssB) has been developed for the serological diagnosis of glanders. The proteins' performance was compared with the OIE reference complement fixation test (CFT) and an indirect enzyme-linked immunosorbent assay (iELISA) on a large panel of sera comprised of uninfected horses (n=198) and clinically confirmed cases of glanders from India and Pakistan (n=99). Using Receiver Operating Characteristics (ROC) analysis and adjusting the cutoff levels, Hcp1 (Se=100%, Sp=99.5%) and GroEL (Se= 97%, Sp=99.5%) antigens exhibited the best specificity and sensitivity. Neither Hcp1 and GroEL proteins, nor iELISA reacted with doubtful and positive CFT samples from glanders free countries which further confirmed the false positive reactions seen in CFT.

High-resolution melting PCR analysis for rapid genotyping of Burkholderia mallei

Burkholderia (B.) mallei is the causative agent of glanders. A previous work conducted on single-nucleotide polymorphisms (SNP) extracted from the whole genome sequences of 45 B. mallei isolates identified 3 lineages for this species. In this study, we designed a high-resolution melting (HRM) method for the screening of 15 phylogenetically informative SNPs within the genome of B. mallei that subtype the species into 3 lineages and 12 branches/sub-branches/groups. The present results demonstrate that SNP-based genotyping represent an interesting approach for the molecular epidemiology analysis of B. mallei.

Liposomised recombinant ribosomal L7/L12 protein protects BALB/c mice against Brucella abortus 544 infection

Brucella abortus, a facultative intracellular pathogen, is of tremendous zoonotic importance because of its ability to induce spontaneous abortion in cattle and other livestock. It is also known to cause persistent undulant fever, endocarditis, arthritis, osteomyelitis and meningitis in humans. The available vaccines against this dreadful infection suffer from limitations like short-term immunity, increased risk of hypersensitivity and low prophylactic index in the recipients. In the present study, we have demonstrated that liposomal form of a recombinant ribosomal L7/L12 protein, a B-T cell antigen of B. abortus, activates strong immune response in the host. In contrast, free antigen generates moderate immune response in the immunised animals. The liposomisation of rL7/L12 protein causes tremendous increase in cell-mediated immune response in terms of delayed type hypersensitivity, T-cell proliferation and up-regulation in type I cytokine expression, etc. Moreover, the liposome encapsulated antigen elicited stronger humoral immune response as compared to standard vaccine (S-19) or IFA-L7/L12 combination in the immunised animals. The effectiveness of liposome-based vaccine was also substantiated by better systemic clearance of bacterial load after challenging the animals with B. abortus 544 pathogen. The results of the present study suggest the potential of liposome-based rL7/L12 antigen as prospective and efficient candidate vaccine capable of eliciting both cell mediated as well as humoral immune responses against experimental murine brucellosis.