NOVEL SMALL MOLECULE-ANTIBIOTIC COMBINATIONS TO ERADICATE MULTIDRUG-RESISTANT BACTERIA

Abstract

Antibiotics are one of those candidates who have shaped modern human history and civilization. Antibiotic resistance is defined as the ability of a bacteria to avert antibiotic action against it. As a result, regular treatments become ineffective, infections persist, and may spread to others. Antibiotic resistance is one of the major threats to global health, food security, and development today. Antibiotic resistance can have an impact on anyone, of any age, in any country. Antibiotic resistance is a natural phenomenon, but the misuse of antibiotics has accelerated this process. A growing number of human infections – such as septicemia, pneumonia, tuberculosis, gonorrhoea, and salmonellosis – are becoming harder to treat as the antibiotics used to treat them are becoming less effective day by day. Antibiotic resistance results in a longer hospital stay, higher medical costs, and increased mortality. Combinations of antibiotics are a well-known method for treating certain diseases that are multidrug resistant. The theme of this thesis is based on a strategy to explore the potential of two novel antibacterial molecules and an efflux pump inhibitor molecule, to potentiate or broaden the spectrum of the efficacy of polymyxin B, vancomycin, and fosfomycin, respectively. The screenings were conducted on the whole cell system or purified validated target proteins. Different aspects of bacterial physiology that underpin resistance mechanisms for blocking efflux pumps were also considered. In this thesis, a broad-spectrum antibacterial small molecule, IITR00693 (2-Aminoperimidine) was studied. IITR00693 was found to be active against the ESKAPE (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp.) pathogens. The efficacy of this novel small molecule (IITR00693)-polymyxin B synergistic combination was explored and established against S. aureus and P. aeruginosa. Another vancomycin-intermediate Staphylococcus aureus was considered and a 5-nitrofuraldehyde (NFA) molecule was introduced. It is a small nonhemolytic and noncytotoxic novel nitrofuran molecule that could potentiate vancomycin activity against vancomycin-intermediate Staphylococcus aureus (VISA). The study found that the combination of NFA and vancomycin could inhibit the growth of the bacteria in a mice model. In a previous project, a research team from our group investigated the reason for the intrinsic resistance of A. baumannii against fosfomycin, and the reasons for low cellular concentration were found to be the inefficient uptake and an active efflux pump AbaF (fosfomycin using Acinetobacter baumannii-specific fosfomycin efflux pump). AbaF played a significant role in fosfomycin intrinsic resistance, and thus in this study, it was used as a target to revive the efficacy of fosfomycin against A. baumannii. An efflux pump inhibitor screening was performed against E. coli KAM32/pUC18_abaF (an efflux deficient E. coli strain carrying AbaF gene cloned in pUC18 plasmid) using the non-inhibitory concentration of twenty-four putative efflux pump inhibitors. Overall, three novel small molecule-antibiotic combinations were studied in this thesis. They have been evaluated for efficacy, toxicity, and mechanistic insights. These results can be used to build new antibacterial treatments to combat the growing AMR.