Table 2. Summary of studies of the gut microbiome in psoriasis.

Bacteria
Study	Study Design	Methods	Major findings
Masallat et al.	- Fecal samples from 45 PsO, 45 age and sex matched C	16s rRNA using 3 sets of specific primers for 3 phyla (Bacteroidetes, Firmicutes, and Actinobacterial)	Phyla ↓ Actinobacteria in Pso vs. C, negatively correlated with PASI ↑ Firmicutes/Bacteroidetes ratio in Pso vs. C, positively correlated with PASI
Scher et al.	- Fecal samples from 17C, 16 PsA, 16 Pso who were recently diagnosed and had never been treated with DMARD's, oral or systemic therapies - Secretory Ig A, pro-inflammatory proteins, fatty-acids from fecal supernatant and serum	16s rRNA (V1, V2)	Phyla ↓ Firmicutes, Clostridiales, Verrucomicrobiales in PsA vs. Pso ↑ Bacteroidetes in PsA vs. Pso ↓ Actinobacteria in Pso vs. C Genera ↓ Akkermansia, Ruminoccocus, Pseudobutyrivibrio in PsA vs. C ↑ Coprobacillus in PsA vs. Pso ↓ Parabacteroides and Coprobacillus in Pso vs. C

Abbreviations: Pso = Psoriasis, PsA = Psoriatic arthritis, C = control, L = lesional, NL = non-lesional, AD = atopic dermatitis, HPV = Human papillomavirus, PASI = Psoriasis Area Severity Index, PCR = Polymerase chain reaction, MTX = Methotrexate, PUVA = Psoralen and ultraviolet A radiation; DMARD = Disease-modifying antirheumatic drug