The skin harbors a complex and dynamic microbiota constituted by numerous microorganisms that live in symbiosis with the host. The specific etiology of psoriasis is still not-well understood; nonetheless several studies highlighted that that the skin microbiota could have a pivotal role in the maintenance and/or progression of the disease, acting as microbial predictor of psoriasis however.

The aim of the present study was to characterize the microbiota of cutaneous biopsies associated to guttate and vulgaris psoriasis, both considering lesion and healthy skin belonging to the same psoriatic subject.

Twelve individuals with guttate psoriasis and 12 individuals with vulgaris psoriasis have been enrolled at Dermatological Unit of IRCCS Galeazzi Institute, Milan.

Patients selected for the psoriasis vulgaris group had a course of disease stable for at least 1 month before collection. The second group presented guttate psoriasis, defined as "eruptive", that is characterized by a rapid appearance and worsening of the clinical presentation within the month preceding the visit.

From each participant, a punch was used to obtain a cutaneous sample from both a lesion and healthy skin area of 2 mm2 belonging to the left gluteus, for a total of 48 biological samples. Participants were selected and included in the study according to the following criteria: i) over 18 years of age; ii) use of a free-preservatives soap with moisturizing function; iii) no use of probiotics; iv) no use of antibiotics; v) no treatment with corticosteroids, biological drugs, methotrexate or retinoids in the month prior the sampling; vi) no use of topical corticosteroids, vitamin D derivatives or phototherapy; vi) no chronic or systemic infections; vii) no cutaneous acute infections; viii) no allergy to pollen, food and drugs ix) no pets. Informed consent was obtained from all subjects.

A metagenomics approach, performed by the use of Ion torrent Personal machine, were used to investigate the bacterial composition of the skin microbiota associated to each samples collected.

After sequencing, the data analysis were focused on the bacterial biodiversity and microbial networks existing in the skin microbiota to evaluate a hypothetical role of bacteria in the complex pathophysiological mechanisms involved in psoriasis.

Inclusion Criteria:

• over 18 years of age;
• use of a free-preservatives soap with moisturizing function, applied once a day;pets.

Exclusion Criteria:

• no use of probiotics in the month prior the sampling;
• no use of antibiotics in the month prior the sampling;
• no treatment with corticosteroids, biological drugs, methotrexate or retinoids in the month prior the sampling;
• no use of topical corticosteroids, vitamin D derivatives or phototherapy in the month prior the sampling;
• no chronic or systemic infections;
• no cutaneous acute infections during sampling;
• no allergy to pollen, food and drugs
• no pets.

Twelve individuals with guttate psoriasis and 12 individuals with vulgaris psoriasis have been enrolled at Dermatological Unit of IRCCS Galeazzi Institute, Milan.

Patients selected for the psoriasis vulgaris group had a course of disease stable for at least 1 month before collection. The second group presented guttate psoriasis, defined as "eruptive", that is characterized by a rapid appearance and worsening of the clinical presentation within the month preceding the visit.