Education and training:

Dr. Girish K. Radhakrishnan obtained MSc in Microbiology (1999) from School of Biosciences, Mahatma Gandhi University, Kerala and PhD in Biotechnology (2006) from School of Biotechnology, Madurai Kamaraj University, Tamil Nadu. He did his postdoctoral research (2006-2010) at the University of Wisconsin-Madison, USA and worked as Research Assistant Professor at the same university (2010-2012). He joined NIAB on 03 December 2012.

We study various aspects of the infectious intracellular bacterial pathogen Brucella, which causes the worldwide zoonotic disease brucellosis. This disease poses a serious veterinary and public health challenge in India, with estimated annual median losses of ₹28,300 crores. There is no human vaccine available, and existing animal vaccines have significant drawbacks. Treatment with antibiotics is often ineffective due to frequent failures, prolonged therapy with multiple drugs, and relapse. Diagnosis is complicated by atypical symptoms and the low sensitivity and specificity of current serodiagnostic assays. Compared to other bacterial pathogens, limited information exists on the virulence mechanisms that enable Brucella to survive and replicate within the host.

Our research aims to elucidate the virulence mechanisms by which Brucella invades phagocytic cells and modulates host innate and adaptive immune responses to promote chronic infection. We employ a range of genomic and proteomic techniques such as, LC-MS, Bioorthogonal Non-canonical Amino Acid Tagging (BONCAT), CRISPR-Cas9 gene editing, siRNA, lentivirus/AAV-based gene delivery, functional genomic yeast screening, Transposon Insertion Sequencing (TIS), and infection studies using gene knockout mice. We work with zoonotic Brucella species in the BSL-3/A-BSL-3 facility at NIAB. Our ultimate goal is to develop improved vaccines, therapeutics, and diagnostic assays for both animal and human brucellosis. 

Identification of Immunodominant Antigens and Development of Diagnostics and Vaccines for Brucellosis.
Identifying and characterizing immunodominant antigens secreted or shed by Brucella in the host bloodstream provides critical insights into its virulence and pathogenesis. These antigens are valuable for developing improved sero-diagnostic assays and next-generation vaccines for both animal and human brucellosis.

To identify novel immunodominant antigens, we performed high-throughput immunoprobing of a Brucella melitensis protein microarray using serum samples from infected cattle, goats, dogs, and humans. This analysis revealed antigens that are either shared across or unique to different host species (Frontiers in Microbiology, 2023). Based on these findings, we developed novel serodiagnostic assays and multi-epitope vaccine candidates for brucellosis.

Development of DIVA-compatible Serodiagnostics: Early detection of brucellosis in livestock is key to controlling transmission to humans. Current serodiagnostic assays suffer from limitations such as low sensitivity/specificity and inability to Differentiate Infected from Vaccinated Animals (DIVA). We developed a lateral flow assay (LFA) and indirect ELISA (iELISA) capable of distinguishing naturally infected animals from those vaccinated with S19 (DIVA capability). These kits are affordable, suitable for use in both animals and humans, and demonstrate high diagnostic performance. A patent application for these diagnostics has been filed, and the technology has been transferred to Engrave Bio Labs Pvt. Ltd. for commercialization.

Development of Novel Vaccines and Therapeutics for Brucellosis: To develop improved vaccines for brucellosis, we are pursuing two main strategies: multi-epitope vaccines (MEVs) and rationally designed live-attenuated vaccines.

We have generated two MEV candidates based on immunodominant proteins identified in our lab. Both have shown significant protection against Brucella melitensis and Brucella abortus in preclinical studies. A patent has been filed, and technology transfer is underway. In parallel, we have developed two novel live-attenuated vaccine candidates via targeted gene deletions affecting virulence but not in vitro viability. These are currently being evaluated in animal models.

For therapeutics, we are exploring three complementary approaches as represented below:-

We utilize high-throughput screening methods, including high-content screening (HCS), to identify promising therapeutic candidates, with detailed evaluations ongoing. Additionally, we developed a hybrid antibiotic by conjugating gentamicin with peptides derived from the Brucella virulence protein TcpB. This hybrid exhibits enhanced cellular permeability and anti-inflammatory properties, alongside its antimicrobial activity (Nandi et al. 2025, Journal of Inflammation Research).

Studies on Brucella–Host Interaction.
Understanding the complex mechanisms by which Brucella invades macrophages, replicates, and subverts host immune responses is central to our research. Brucella is recognized as a “stealth” pathogen due to its ability to evade both innate and adaptive immune responses, enabling chronic persistence in the host. Some of our key findings are outlined below:-

Brucella induces the expression of the host protein FBXO22, which activates NF-κB and enhances the expression of various phagocytic receptors on macrophages, promoting bacterial invasion. FBXO22 also degraddes anti-inflamamtory virulence proteins of Brucella (Mazumdar et al. 2022. Infection and immunity)

Brucella downregulates the host protein USP8 by targeting the TIRAP/CREB signaling pathway, leading to enhanced expression of CXCR4, a receptor implicated in Brucella entry into macrophages (Joshi et al. 2024. Infection and Immunity)

After invading the host cell, Brucella resides within a membrane-bound compartment known as the Brucella-containing vacuole (BCV), which undergoes sequential maturation through the dynamic recruitment and removal of host proteins essential for bacterial replication and egress. We have optimized methodologies for isolating intact BCVs at different stages of maturation using flow cytometry and magnetic nanoparticles. The proteome of these BCVs will be analyzed using LC-MS to identify both host and Brucella proteins involved in BCV trafficking and maturation, which are critical for intracellular survival and egress. These proteins may serve as potential targets for the development of novel therapeutic and preventive strategies for brucellosis.

The Brucella virulence protein TcpB attenuates NF-κB activation and proinflammatory cytokine production via TLR2/4 signaling by targeting the host protein CLIP170 (Jakka et al. 2018, Journal of Immunology). This study revealed CLIP170 as a novel negative regulator of TLR4 signaling and elucidated its role in the anti-inflammatory effects of the neurosteroid, pregnenolone (Murugan et al. 2019, Journal of Biological Chemistry).

We also demonstrated that TcpB promotes ubiquitination and proteasomal degradation of inflammatory caspases (caspase-1, -4, and -11), thereby suppressing non-canonical inflammasome activation (Jakka et al. 2017, Journal of Biological Chemistry).

Identification of Novel Virulence Genes of Brucella.
We employ high-throughput transposon mutagenesis, yeast-based screening platforms, and Bioorthogonal Non-Canonical Amino Acid Tagging to identify novel Brucella virulence factors. One such gene identified is ArgT, which appears to modulate host nitric oxide (NO) production. Brucella uses ArgT to deplete intracellular arginine, thereby reducing NO production and evading intracellular killing mechanisms (Mallik et al. 2024. Virulence).  A live-attenuated vaccine candidate based on the ArgT knockout strain of B. melitensis has been developed and is currently under evaluation. Another identified virulence gene, BM224, induces the unfolded protein response in host cells and is essential for the survival of Brucella within macrophages and in mice. Detailed characterization of BM224 and other putative Brucella virulence genes is currently underway.

19. Binita Roy Nandi, Biswaranjan Patra, Girish K Radhakrishnan* (2025) A Chimeric Peptide Derived from a Bacterial Effector Protein Attenuates TLR-2/4-Mediated Production of Pro-Inflammatory Cytokines and Enhances the Cellular Availability of Gentamicin. Journal of Inflammation Research 2025 Aug 9;18:10751–10775. https://doi.org/10.2147/jir.s526902

18. Sushree Rekha Mallik, Kiranmai Joshi and Girish K Radhakrishnan* (2024). The arginine/ornithine-binding protein ArgT plays an essential role in Brucella to prevent intracellular killing and contribute to chronic persistence in the host. Virulence 2024 Dec;15(1):2421983. https://doi.org/10.1080/21505594.2024.2421983

17. Kiranmai Joshi, Varadendra Mazumdar, Binita Roy Nandi, Girish K Radhakrishnan* (2024). Brucella targets the host ubiquitin-specific protease, Usp8, through the effector protein, TcpB, for facilitating infection of macrophages. Infection and Immunity, 4 January 2024, e0028923.
DOI: https://doi.org/10.1128/iai.00289-23

16. Subathra Murugan, Binita Roy Nandi, Varadendra Mazumdar, Kiranmai Joshi, Prachita Nandini, Swapna Namani, Padmaja Jakka, Girish K Radhakrishnan* (2023). Outer membrane protein 25 of Brucella suppresses TLR-mediated expression of proinflammatory cytokines through degradation of TLRs and adaptor proteins. Journal of Biological Chemistry 299 (11). DOI: https://doi.org/10.1016/j.jbc.2023.105309

15.  Prachita Nandini, Padmaja Jakka, Subathra Murugan, Varadendra Mazumdar, Deepak Kumar, Richa Prakash, Sukhadeo B Barbuddhe, Girish Radhakrishnan* (2023). Immuno-profiling of Brucella proteins for developing improved vaccines and DIVA capable serodiagnostic assays for brucellosis. Frontiers in Microbiology Sec. Infectious Agents and Disease Volume 14 – 2023 | doi: 10.3389/fmicb.2023.1253349 https://www.frontiersin.org/articles/10.3389/fmicb.2023.1253349/full

14. Varadendra Mazumdar, Kiranmai Joshi, Binita Roy Nandi, Swapna Namani, Vivek Kumar Gupta and Girish Radhakrishnan* (2022). Host F-Box Protein 22 Enhances the Uptake of Brucella by Macrophages and Drives a Sustained Release of Proinflammatory Cytokines through Degradation of the Anti-Inflammatory Effector Proteins of Brucella. Infection and Immunity 90(5):e0006022. doi: 10.1128/iai.00060-22. https://pubmed.ncbi.nlm.nih.gov/35420446/

13. Subathra Murugan, Padmaja Jakka, Swapna Namani,Varadendra Mujumdar and Girish Radhakrishnan* (2019). The neurosteroid, pregnenolone promotes degradation of key proteins in the innate immune signalling to suppress Journal of Biological Chemistry 294 (12) 4596-4607.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6433066/

12. Padmaja Jakka, Swapna Namani, Subathra Murugan, Nivedita Rai and Girish Radhakrishnan* (2018). The Brucella effector protein TcpB induces degradation of inflammatory caspases and thereby subverts non-canonical inflammasome activation in Journal of Biological Chemistry 292 (50), 20613-20627.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5733597/

11. Padmaja Jakka, Bindu Bhargavi, Swapna Namani, Subathra Murugan, Gary Splitter and Girish Radhakrishnan* (2017). Cytoplasmic Linker Protein CLIP170 Negatively Regulates TLR4 Signaling by Targeting the TLR Adaptor Protein Journal of Immunology 200 (2) 704-714.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5760445/

10. Sarwar Azam, Sashi Bhushan Rao, Padmaja Jakka, Veera NarasimhaRao, Bindu Bhargavi, Vivek Kumar Gupta, and Girish Radhakrishnan* (2016). Genetic Characterization and Comparative Genome Analysis of Brucella melitensis Isolates from International Journal of Genomics. Volume 2016 (2016),13 pages.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4976149/

9. Splitter G, Harms J, Petersen E, Magnani D, Durward M, Rajashekara G, Radhakrishnan  (2014) Studying host-pathogen interaction events in living mice visualized in real time using biophotonic imaging. Methods Mol Biol. 2014;1197:67-85.https://pubmed.ncbi.nlm.nih.gov/25172275/

8. Sashi Bhushan Rao, Vivek Gupta,Mukesh Kumar, Nagendra R. Hegde, Gary A. Splitter, Pallu Reddanna and Girish K. Radhakrishnan* (2014). Draft Genome Sequence of the Field Isolate Brucella melitensis strain BM IND-1 from India. Genome Announcements 2(3):e00497-14. doi:10.1128/genomeA.00497-14.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4038885/

7. Smith, A. Magnani. D, Kahn. M , Harms. J, Durward. M, Radhakrishnan. G, Liu, Y- P and Splitter, G (2013). Brucella Induces an Unfolded Protein Response via TcpB that Supports Intracellular Replication in Macrophages. PLoS Pathogen, 9(12): e1003785. doi:10.1371/journal.ppat.1003785.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3855547/

6. Radhakrishnan, G.  and Splitter, G. (2012) Modulation of host microtubule dynamics by pathogenic bacteria. Biomolecular Concepts. 3 (6), 571–580.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3625037/

5. Gupta VK, Radhakrishnan G, Harms J, Splitter G. (2012) Invasive Escherichia coli vaccines expressing Brucella melitensis outer membrane proteins 31 or 16 or periplasmic protein BP26 confer protection in mice challenged with B. melitensis. Vaccine, 30, 4017- 4022.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3361596/

4. Durward M, Radhakrishnan G, Harms J, Bareiss C, Magnani D and Splitter, G. A (2012) Active Evasion of CTL Mediated Killing and Low Quality Responding CD8+ T Cells Contribute to Persistence of Brucellosis. PLoS ONE 7(4): e34925.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3338818/

3. Radhakrishnan, G, Harms, J and Splitter, G (2011). Modulation of microtubule dynamics by a TIR domain containing protein from an intracellular pathogen Brucella. Biochemical Journal 439 (1) 79-83.https://pubmed.ncbi.nlm.nih.gov/21692747/

2. Radhakrishnan, G and Splitter, G. (2010).Biochemical and functional analysis of TIR domain-containing protein from Brucella melitensis. Biochemical and Biophysical Research Communications 397(1) 59-63.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2900483/

1. Radhakrishnan, G. K., Yu, Q., Harms, J. S., Splitter, G. A. (2009). Brucella TIR domain- containing protein mimics properties of the toll-like receptor adaptor protein TIRAP. Journal of Biological Chemistry 284(15): 9892-9898.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2665112/

Ongoing extramural research grants:

1. Understanding the role of an Ubiquitin Specific Peptidase in the invasion and intracellular replication of the zoonotic bacterial pathogen, Brucella
Funding agency: DBT
Duration: February 2022 to February 2025

2. Studies on the immunodominant proteins of the zoonotic pathogen, Brucella to develop improved diagnostic assays and vaccines for brucellosis.
Funding agency: DBT
Duration: September 2021 to September 2024

3. Development, evaluation and validation of peptide-based iELISA for the zoonotic diseases, (1) Brucellosis and (2) Coxiellosis (Q-fever).
Funding agency: DBT-NER
Duration: March 2021 to March 2023

Completed extramural research grants:

1. To understand the role of Cytoplasmic linker protein-170 in the down-regulation of TLR4 signaling. Funding agency: DBT.

2. Understanding the mechanism of host innate immune suppression by the Brucella effector protein, TcpB to identify novel drug targets for brucellosis. Funding agency: DST-SERB.

3. Development of peptide-based anti-inflammatory drug for septicemia. Funding agency: DST-DPRP.

4. To develop novel therapeutics for brucellosis: Identification and characterization of host factors supporting Brucella replication. Funding agency: DBT.

5. Understanding the immune mechanism of host disease resistance and development of marker vaccines and DIVA tests for Peste des Petits Ruminants (PPR). Funded by DBT-BBSRC (multi-institutional project). Funding agency: DBT-BBSRC.

Laboratory of Immunology and Microbial Pathogenesis
National Institute of Animal Biotechnology (NIAB),
Opp. Journalist Colony, Near Gowlidoddi,
Extended Q City Road, Gachibowli,
Hyderabad, Telangana-500 032,
India.

Email: girish[at]niab[dot]org[dot]in
Tel: +91-(0)40-2312-0142

Development of “Differentiating Infected from Vaccinated Animals (DIVA)” capable serodiagnostic assays for brucellosis:
Early detection and control of brucellosis in livestock is crucial for controlling the disease in humans. Existing serodiagnostic assays for brucellosis have many disadvantages such as poor sensitivity/specificity and lack of DIVA capability. We developed an indirect ELISA using an immunodominant protein (BM5) from Brucella for serodiagnosis of brucellosis in animals and humans. The BM5-ELISA can detect anti-Brucella antibodies in the Brucella-infected animals and humans with high specificity and sensitivity. The BM5-ELISA can efficiently differentiate Brucella abortus S19-vaccinated from naturally infected cattle. We developed recombinant BM5 protein as well as peptide (14 amino acids)-based ELISAs.

Patent awarded: –

1. Invention: Novel anti-inflammatory peptides.
Patent number: 556338

Patent applications filed:-

1. Cell permeable peptides; Indian Patent application no. 202141048139

2. Immunodominant protein and peptide-based brucellosis diagnosis kits and devices to differentiate infected animals from Brucella abortus S19-vaccinated animals. Indian Patent Application No. 201941010993

3.  Kits and devices for diagnosis of brucellosis and differentiation of infected animals from vaccinated animals.
Indian patent application no. 201941010993

4. Brucella tandem peptide protein candidates bru-tpp-i and bru-tpp-ii and method for development thereof.
Indian patent application no. 202541056122

Technology Transferred:-

BM5 protein/peptide-based brucellosis diagnostic assays with DIVA capability

Company: Engrave Bio Labs, Hyderabad

Web links
Pubmed: https://www.ncbi.nlm.nih.gov/pubmed/?term=Girish+Radhakrishnan
Google Scholar Link: https://scholar.google.com/citations?user=IEFTDcAAAAAJ&hl=en

Postdoctoral Research Opportunities are available.