Membrane Porins: An alternative key to combat bacterial Infections

Work done in the lab of Prof. Dipshikha Chakravortty at the Department of Microbiology and Cell Biology in the Indian Institute of Science, Bengaluru

About author

Atish Roy Chowdhury completed his bachelor’s degree in Microbiology with a Physics and cChemistry minor at St. Xavier’s College, Kolkata (West Bengal). He joined Bose Institute, Kolkata, to obtain his master’s degree in Life Sciences with a specialization in Molecular Cell Biology. Following, Atish undertook doctoral research at the lab of Professor Dipshikha Chakravortty at the Department of Microbiology and Cell Biology in the Indian Institute of Science, Bengaluru. where he was engaged in characterizing the role of outer membrane porins in antimicrobial resistance and pathogenesis of Salmonella Typhimurium.

Interview

How would you explain your research outcomes to the non-scientific community?

During my doctoral research at the Indian Institute of Science (IISc), I worked with Salmonella Typhimurium, a Gram-negative pathogen that causes self-limiting gastroenteritis and diarrhea in humans. This pathogen is associated with severe bloodstream infection in sub-Saharan Africa. My work aimed to understand the role of outer membrane porins in the virulence and antimicrobial resistance of Salmonella.

We can compare the bacterial outer membrane porins with the windows on the walls of our room. The walls protect us from external dangers when we are inside the room. Simultaneously, the windows we can use for the passage of fresh air. Bacterial pathogens are also very smart. They use their outer membrane as an impenetrable barrier against external threats such as antibiotics, reactive oxygen (ROS), and nitrogen species (RNI) in macrophages. At the same time, the outer membrane porins assist in transporting nutrients (minerals, amino acids, sugars, etc.) across the membrane. During a storm, we shut down the windows to stop the entry of dust particles and rain inside the room. Similarly, when Salmonella experiences any significant threat, it alters the permeability of its outer membrane with the help of porins. This stealthy yet intelligent strategy made Salmonella infection nearly incurable.

Using genetic engineering tools, I have removed these porins from the outer membrane of Salmonella to see how bacteria respond to antibiotic therapy and the innate immune response of phagocytes.

How do these findings contribute to your research area?

With thorough research, I have identified one outer membrane porin (or Omp) in Salmonella named OmpA, which executes a multifaceted role in protecting the bacteria from the host innate immune response and antibiotic therapy.

Host macrophages have highly robust innate immune arsenals such as ROS, RNI, and antimicrobial peptides to deal with invading pathogens. But Salmonella can easily overcome the host immune response with the help of two pathogenicity islands named SPI-1 and SPI-2. My study revealed that deleting OmpA from Salmonella makes the bacteria replication-deficient in macrophages. The pore size of OmpA is smaller than any other outer membrane porins. It is an intelligent strategy of Salmonella to express OmpA in the harsh environment of macrophages so that it can restrict the entry of ROS/ RNI and replicate successfully. In the absence of OmpA, the enhanced expression of another porin OmpF (with a larger pore size) compromised the stability of the bacterial outer membrane and made the bacteria susceptible to intracellular nitrosative stress.

I further showed that OmpA deficiency allows the entry of β-lactam antibiotics (ceftazidime and meropenem) in Salmonella. In the absence of OmpA, the antibiotics disintegrated the bacterial envelope and facilitated the release of genomic DNA. Altogether, my study establishes OmpA as an essential virulence factor of Salmonella Typhimurium.

What was the exciting moment during your research?

During the initial days of my Ph.D. (early 2017), when I was a novice and learning different lab techniques, I struggled with simple plasmid isolation and PCR amplification. It took more than a month for me to learn plasmid isolation properly. Every day I used to run multiple gels to determine whether my PCR had worked and ended up with empty gels. Due to consecutive failures, I started thinking that doing a Ph.D. was not my cup of tea, and that I would return to Kolkata. However, I didn’t quit. One fine morning at 3:30 AM, I found that my PCR had worked. The thick purple bands of PCR-amplified products on the UV transilluminator gave me immense happiness, and I went to bed completely satisfied. After so many years, I still feel motivated and excited whenever I think about that incident.

“This study establishes OmpA as an essential virulence factor of Salmonella Typhimurium.”

What do you hope to do next?

My doctoral research gave me adequate opportunities to learn about the behaviour of microbial pathogens during infection and antibiotic treatment. Using this knowledge, I wish to explore more in the field of ‘host-pathogen interaction’ and ‘antimicrobial resistance’ in my postdoc to design novel antimicrobial therapeutics.

Where do you seek scientific inspiration from?

My mother is my most significant source of inspiration to do scientific research. I also get continuation motivation from my Ph.D. supervisor Prof. Dipshikha Chakravortty (Department of Microbiology and Cell Biology, IISc, Bengaluru). From the first day in the lab, she taught me how to ask and think independently to solve novel scientific questions. She gave me immense liberty to conduct research to execute my scientific thoughts. I got scientific inspiration from my colleagues in the lab and other faculties of our department as well.

How do you intend to help Indian science improve?

I firmly believe that India has a lot of talent and potential to do quality research. The willingness of young Indian researchers to get involved in performing fundamental and translational research is unparalleled. However, we need more sincere attention, significant funding, and industrial exposure in research to match the international level and attract talent to Indian labs. Simultaneously, collaboration and regular student exchange programs between Indian institutes and the top universities worldwide can also improve Indian science.

Reference

Roy Chowdhury, A., Sah, S., Varshney, U., & Chakravortty, D. (2022). Salmonella Typhimurium outer membrane protein A (OmpA) renders protection from nitrosative stress of macrophages by maintaining the stability of bacterial outer membrane. PLoS pathogens, 18(8), e1010708. https://doi.org/10.1371/journal.ppat.1010708

Chowdhury, A. R., Mukherjee, D., Singh, A. K., & Chakravortty, D. (2022). Loss of outer membrane protein A (OmpA) impairs the survival of Salmonella Typhimurium by inducing membrane damage in the presence of ceftazidime and meropenem. The Journal of antimicrobial chemotherapy, dkac327. Advance online publication. https://doi.org/10.1093/jac/dkac327

Copy Editor

Nivedita Kamath

Postgraduate in Biotechnology

Nivedita is a Postgraduate in Biotechnology, with one year Project Assistantship experience at inStem, DBT. She is currently a UPSC aspirant planning to appear for 2021 CSE. Although switching from science career to focus on governance policy and administration, her love for science remains ever-etched in all that she does. On her journey from a researcher toward public administrator, she believes in the critical role of science communication and journalism in bridging the gap between lab benches and public fields. Being part of BioPatrika is her being one stone laid for that very bridge.

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