Batteriofagi di Vibrio cholerae come strumento potenziale di prevenzione e controllo del colera.

Cholera is still a major public health threat, especially in developing countries. Treatment and control of cholera consist in rehydratation and sanitary improvements, while antibiotics could shorten the infection-span. Yet, the increasing antibiotic resistance and the lack of a performant vaccine impose new strategies. Bacteriophages (phages) that infect Vibrio cholera can be a potential, sustainable complement and/or alternative to antibiotic treatment. In the past 10 years more than 60% of the reported cholera cases occurred in Africa, with the largest percentage in the Democratic Republic of Congo (DRC), where cholera is endemic. The aim of this thesis work was the isolation, preliminary characterization, and evaluation of V. cholera phages for the potential control and eventual treatment of cholera. Phages were isolated (n=55, Haiti, 2016) via plaque purification and spotted against the V. cholera strains (n=44, DRC, 2014-2017) to assess the host range: 5 different were isolated and none of the bacterial strains tested showed resistance to all phages, while their antibiotic resistance (Kirby-Bauer) spans through high (100% for Colistin sulfate and Streptomycin) to mild (2% for Gentamicin). Rep-PCR-fingerprinting of bacterial isolates revealed high similarity (>97%), suggesting a possible clonality. Phage titers were stable for 1 month, and the effects of different temperatures [35°C, 37°C, 40°C], pH [5, 7.5, 8] and salinity [NaCl: 0%, 1%, 3%]) on phage adsorption (phages: φ26P, φ37B) suggest the phage potential use in cases of hypothermia or high fever, while neutral pH and 1% NaCl could be ideal conditions for applications. Phage-genome sequencing (Illumina) showed high similarity to Vibrio-virus phiVC8 and VP2. They harbour IG-like domains, enabling gut-mucus attachment, important for phage colonization, while no toxin, neither antibiotic resistant genes were detected. Five phages showed potentialities for the biocontrol of V. cholerae, given their high effectiveness against cholera strains. It is noteworthy that phages from Haiti, despite the geographical distance, could infect target bacteria isolated in the DRC during a 3 years time frame and showed very little diversity. The V. cholera isolation sites are representative of the DRC area, being a good candidate panel for phage testing.