• Basidiomycetes fungi
• Biofilm
• Caratterizzazione molecolare
• Grifola frondosa
• Listeria monocytogenes
• MLST
• MvLST
• saggio formazione biofilm
• saggio scettibilità biofilm
• Sequence Type
• Serotype
• Tipizzazione genica
• Virulence Type

Listeria monocytogenes is a ubiquitous, Gram-positive, nonsporegenic, facultatively aerobic-anaerobic, motile with peritric cilia, able to cause infections in mammals. Some strains of L. monocytogenes, in addition to surviving as environmental saprophytes, can colonize humans and behave as facultative intracellular pathogens causing an infection known as listeriosis. Listeriosis can be contracted by humans mainly through the ingestion of contaminated food and therefore represents a zoonotic disease of food origin. Although this infection occurs with sporadic incidence (0.46 cases per 100,000 in 2019 in Europe), in the context of zoonotic diseases it is associated with the highest rate of hospitalization (92,1%) and lethality (17.6%), representing a worrying public health problem.
Epidemiological surveillance of listeriosis is essential for identifying sources of contamination, food vectors and the presence of outbreaks of infection, to contain the spread of L. monocytogenes strains.
The purpose of this thesis was to characterize from a genotypic and phenotypic point of view 23 clinical strains of L. monocytogenes isolated from patients hospitalized at the main Palermo hospitals from 31 December 2018 to July 2020 (collected by “Policlinico Universitario Paolo Giaccone” hospital), to evaluate their susceptibility profile to antibiotics and the bactericidal action of the extract obtained from the Grifola frondosa mushroom.
A molecular characterization of the isolates received was carried out using multiplex PCR, Multilocus sequence typing (MLST) and Multi-virulence-locus sequence typing (MvLST).
Further analysis by PCR and subsequent electrophoretic run in agarose gel of the amplification products allowed to evaluate the presence/absence of the main genes included in the four Listeria pathogenicity islands (LIPI), identified to date.
For all strains, the susceptibility profiles to antibiotics were evaluated by automated methods, which involved the use of the BD Phoenix ™ Instrument with the relative panels for Gram positive (PMIC-ID-88) for the determination of the minimum inhibitory concentration (MIC) against 24 antibiotics.
In addition, the more traditional Kirby Bauer method (susceptibility to agar-diffusion antibiotics) was used to test the sensitivity/resistance of clinical isolates to meropenem, an antibiotic not included among those evaluated by the PHOENIX panels, however required by the EUCAST guidelines since intended for the treatment of L. monocytogenes.
For each clinical strain, the ability to form biofilms was assessed by staining the biomass with violet crystal and measuring the optical density of the stain extract.
This procedure was also used to evaluate the antibiofilm activity of the extract from the Grifola frondosa fungus towards L. monocytogenes.