“The biggest threat to human life comes from the smallest bugs,” reminded Prof. Anindya Sundar Ghosh, In-Charge of Molecular Microbiology Laboratory, Department of Biotechnology, IIT Kharagpur. He was recently at Birkbeck’s (University of London) Department of Biological Sciences to talk on “Penicillin interactive enzymes and tackling ß-lactam resistance in mycobacteria”. The occasion was provided by an international capacity-building workshop on the subject of antimicrobial resistance sponsored by the global challenges research fund (GCRF).
Prof. Ghosh says, “The development of antimicrobial resistance is an evolutionary process and is inevitable as it involves the transfer of genes from one bacterium to another. Unless we increase our understanding of how infectious microbes keep evolving and develop resistance towards the antimicrobials used against them, we will never be able to protect ourselves from these life-threatening pathogens. But if we are able to spread awareness among the public and healthcare professionals, we will possibly be able to reduce the excessive use of antibiotics which will, in turn, prevent further aggravation of this problem that is already a serious threat to human existence.”
The Molecular Microbiology Laboratory (MMBL) of the Department of Biotechnology, IIT Kharagpur is involved in antimicrobial research with special emphasis on cell wall modulating penicillin-interactive enzymes including beta-lactamases in four different species of bacteria, namely, E. coli, Acenitobacter baumannii, Klebsiella pneumoniae and Mycobacterium smegmatis. At the workshop at Birkbeck, Prof. Ghosh highlighted his team’s research on Mycobacterium smegmatis.
Antibiotics of the beta-lactam group are extremely popular and hold the lion’s share in the antibiotic market. Due to their property of selective toxicity, beta-lactam antibiotics are extremely effective. These drugs target only the bacterial cell wall – peptidoglycan – and since this is not present in humans and animals, they do not harm the host. It is precisely because they are so effective, and hence popular, that there arises the threat of their misuse.
Prof. Ghosh says, “Mycobactrerial cell wall peptidoglycan (PG) is synthesized and remodelled by a set of transglycosylases and transpeptidases, though very little knowledge is available on their physiological actions. So far the known transglycosylases are PonA1 and PonA2 & transpeptidases are PBPA, PBPB, LdtA and LdtB. The unique feature of mycobacterial PG is that it is crosslinked upto 80% and it contains non-traditional 3–3 peptide crosslinks instead of traditional 4–3 crosslinks. However, very little is known about the remodelling of PG in mycobacteria.”
His team has discovered the physiology of two enzymes – MSMEG_2433 and MSMEG_2432 – possessing DD-carboxypeptidase activities that help in the peptidoglycan remodelling activities. The physiological role of these enzymes is established through various molecular genetics and biochemical studies, including mutational analysis. These two enzymes together help in the maintenance of 3-3 crosslinks in mycobacterial PG, the deletion of which converts the cross-link pattern from 3-3 to 4-3 and renders the cell wall leaky (Pandey et al, Journal of Bacteriology, 2018).
At the workshop Prof. Ghosh brought attention to the fact that MSMEG_2433 is a dual enzyme possessing both DD-carboxypeptidase and beta-lactamase activities (Bansal et al, Microbiology, 2015). These activities are influenced by a glutamic acid residue (G75) present in the omega-like loop of this enzyme, which in turn makes G75 a potential target for synthesis of inhibitory peptides that can be used in the future antimicrobial chemotherapy against mycobacterial infections.
A key area of research in MMBL is the discovery or synthesis of novel and efficient antibacterial drug molecules. In fact, a group of researchers in MMBL is exploring the antibacterial efficacy of various combinations of antibiotics and nano-particles. Birkbeck University features prominently in its scheme of things. Prof. Ghosh is already working in collaboration with Birkbeck’s faculty in designing inhibitors for beta-lactamases and other proteins that interact with penicillins and prevent their antibiotic action. At the workshop he set out several more opportunities for collaborative research, including finding molecules that prevent the formation of drug-resistant microbial biofilms.
Prof. Ghosh pointed out, “We need a worldwide drive against the menace of antimicrobial resistance. This may be through direct and indirect collaborative research that might subsequently help develop a combined front in antimicrobial research with sufficient funding from the international and national funding authorities.”
In this context it would be important to point out that IIT Kharagpur’s Department of Biotechnology organized an international conference entitled “International Conference on Contemporary Antimicrobial Research (ICCAR-2018)” in association with the Society for Antimicrobial Research (SAR). The conference focussed on the development of public awareness on antimicrobial resistance, networking of researchers around the globe, effective antibiotic effluent treatment, increased involvement of healthcare professionals and above all, the urgent requirement of sufficient funds for antimicrobial research.
