Ricciardelli, Annarita (2019) Sustainable use of marine biodiversity as source of novel anti-biofilm agents in industrial and clinical settings. [Tesi di dottorato]

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Amongst marine bacteria, cold-adapted microorganisms represent an untapped reservoir of biodiversity endowed with an interesting chemical repertoire able to synthesize a broad range of potentially valuable bioactive compounds, including antimicrobial activity. The rapid emergence of resistant bacteria is occurring worldwide, endangering the efficacy of antibiotics. One of the main causes of antibiotic resistance is the capability of microorganisms to associate into communities of cells called biofilms. These complex structures provide protection from potential stressors, including the lack of water, high or low pH, or the presence of substances toxic to microorganisms such as antibiotics, antimicrobials or heavy metals. Therefore, coordinated efforts to implement the arsenal of novel anti-infective treatments are greatly needed. In this contest, my PhD project aimed to the sustainable exploitation of Polar marine biodiversity in an attempt to find viable sources of novel anti-biofilm agents, in particular acting against Staphylococcus epidermidis, one of the most common causes of infections associated with medical devices. In detail, during the first part of my project, I focused on the study of the Antarctic marine bacterium Pseudoalteromonas haloplanktis TAC125 and of its ability to produce anti-biofilm molecules, then, on the purification, identification and characterization of the active molecule produced. By setting up of a strategy for the large scale biofilm cultivation of the Antarctic bacterium, the production yield of P. haloplanktis TAC125 anti-biofilm agent was improved, so as to allow the purification and the identification of the active molecule, the pentadecanal. However, as the pentadecanal is a chemically reactive agent, it could easily undergo oxidation reactions, therefore it could not be suitable for all possible anti-biofilm strategies. Therefore, some chemical analogues were synthesized and characterized for their anti-biofilm activity and their possible use in combination with antibiotics were investigated. Then, as a possible clinical application, an anti-biofilm coating system, active against S. epidermidis, was developed, by physical adsorption of pentadecanal and its analogues on polydimethylsiloxane (PDMS), a silicon-based material commonly used for the manufacturing of medical devices. Finally, some physiological studies were dedicated to P. haloplanktis TAC125 biofilm formation in relation with environmental adaptations, with the purpose to explore the potentiality of P. haloplanktis TAC125 in biotechnological field. In the second part of my PhD project, given their only partially explored potential, I have also studied other Polar bacteria belonging to different genera, looking for novel anti-biofilm agents against S. epidermidis. Through the screening of small metabolites and proteins/peptides libraries designed starting from planktonic cultures of Polar bacteria, some promising producer strains were identified and their anti-biofilm activities were characterized. Preliminary purification protocols were set up for each kind of molecules, according to their physico-chemical characteristics. Further studies are still ongoing to identify the structure of the active molecules.

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