Studies on the Effect of Antibiotics on Pseudomonas Aeruginosa Biofilm Formation: Implication in Antibacterial Therapy

Kumar, Abhinash (2022) Studies on the Effect of Antibiotics on Pseudomonas Aeruginosa Biofilm Formation: Implication in Antibacterial Therapy. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Abhinash Kumar (13IP013)) 13IP013.pdf - Submitted Version Restricted to Repository staff only Download (47MB)

Abstract

Bacteria are evolving continuously to have new ways as survival strategies in order to avoid the effect of antibacterial agents on them, thus various infections caused by pathogenic bacteria are becoming more difficult to treat. The ability of bacteria to form biofilm is one of the most important survival strategies that potentiate them to survive under harsh conditions and also to avoid immune responses and tolerate antibiotic treatments. In biofilms, bacteria survive within a self-made matrix called extracellular polymeric substances (EPS) which are constituted of proteins, polysaccharides, lipids and nucleic acids and EPS provide the stability to bacterial biofilms. Pseudomonas aeruginosa isolates KPW.1-S1 and HRW.1-S3, when grown in the presence of sub-minimum inhibitory concentrations (sub-MICs) of gentamicin and tetracycline, intense biofilms were formed with respect to compactness and multi-layer structure and EPS formation. Increased levels of e-DNA and exoproteins were found in biofilm structures grown in the presence of gentamicin and tetracycline as compared to control biofilm. The present study was also focused on exploring antimicrobial properties of the plant extracts. Although the Syzygium cumini and Lantana camara leaves extracts showed antibacterial properties against Pseudomonas aeruginosa strains, sub-MIC of the plant extracts alone or in combination with sub-MIC of antibiotics induced more biofilm formation as compared to the respective control conditions and the increased biofilm formation was found to be associated with increased presence of EPS, increased ROS production and decreased ratio in live/dead cells in Pseudomonas biofilms. The present study further revealed that the aminoglycoside antibiotics and plant leaf extracts mediated induction of biofilm formation in Pseudomonas aeruginosa was associated with differential expression of genes involved in quorum sensing (lasI), maintenance of redox status (PA3529) and quinolone signalling and eDNA release (pqsA). Interestingly, such induction of biofilm formation was also found to be associated with the higher expression of lon gene involved in formation of persister cells which can withstand very harsh conditions including lethal concentrations of antibiotics. Thus, the present study is important in terms of understanding the therapeutic outcome of using antibiotics against Pseudomonas aeruginosa. Future studies on detailed regulatory mechanisms of expression of genes involved in cell signalling and persister cell formation will help to develop better therapeutic strategies against Pseudomonas and other pathogenic bacteria.

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