Synthetic Polymyxin-based Peptides Against Multidrug Resistant Bacteria: A Therapeutic Option
[eng] Pseudomonas aeruginosa and Staphylococcus aureus are nosocomial opportunistic pathogens causing a wide variety of both acute and chronic infections, such as pneumonia, bacteraemia, and urinary tract infections. Immunocompromised patients and those suffering cystic fibrosis show a particularly...
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| Format: | doctoral thesis |
| Status: | Published version |
| Publication Date: | 2019 |
| Country: | España |
| Institution: | Universidad de Barcelona |
| Repository: | Dipòsit Digital de la UB |
| OAI Identifier: | oai:diposit.ub.edu:2445/145701 |
| Online Access: | https://hdl.handle.net/2445/145701 http://hdl.handle.net/10803/668033 |
| Access Level: | Open access |
| Keyword: | Antibiòtics Disseny de medicaments Resistència als medicaments Antibiotics Drug design Drug resistance Pseudomonas Staphylococcus aureus |
| Summary: | [eng] Pseudomonas aeruginosa and Staphylococcus aureus are nosocomial opportunistic pathogens causing a wide variety of both acute and chronic infections, such as pneumonia, bacteraemia, and urinary tract infections. Immunocompromised patients and those suffering cystic fibrosis show a particularly high susceptibility to infection by these microorganisms. Moreover, the increasing frequency of the isolation of multidrug-resistant bacteria (MDR) is a major cause for concern. Polymyxins are cyclic peptides with antimicrobial action against Gram-negative bacteria that have been available since 1949, although they were left largely unused during the seventies because of their nephrotoxicity and the availability of less toxic antimicrobials to which bacteria had not yet developed resistance. The most known polymyxin is colistin; like other cationic polypeptides, colistin is an amphipathic compound and, it is believed that this amphipathic nature is relevant to its activity against bacteria. Hence, the aim of this thesis was to synthesize antimicrobial peptides inspired in colistin scaffold and explore their antimicrobial activity against multidrug resistant bacteria such as P. aeruginosa and S. aureus, determine possible synergistic interactions with commercial antibiotics and explore their mechanisms of action. Synthesis: The main attempt in this first part was to synthesize peptides in solid phase by the Fmoc/tBu method. After synthesis, peptides were purified by preparative HPLC method and finally, peptides were characterized by MALDI-TOF. Antimicrobial activity: This part focused on the study the antimicrobial capacity of our peptides against multidrug resistant bacteria, specially P. aeruginosa and S. aureus. First peptide (AMP38) showed an acceptable antimicrobial activity against P. aureuginosa. Moreover, several imipenem-resistant P. aeruginosa were tested with AMP38 and imipenem showing a quite considerable synergistic action, both with planktonic and sessile bacteria. In addition, two peptides of the same family (CAMP113 and CAMP207) were tested against S. aureus (both planktonic and sessile) showing a surprising antimicrobial action since Gram- positive bacteria are regarding as naturally resistant to polymyxins. Moreover, these peptides showed an inordinately high selectivity index. Mechanisms of action: The final part of this doctoral thesis focused on an initial exploration of mechanisms of action of peptides above mentioned. Transmission electronic microscopy (TEM) assays were performed in order to elucidate possible interactions between peptides and outer membrane of Gram-negative bacteria. In addition, isothermal titration calorimetry assays were carried out to determine peptide-teichoic acid interactions. Data obtained from these studies are promising, being able to be a therapeutic alternative for infections produced by multidrug resistant bacteria. |
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