Occurrence of subtypes in patients from Italy revealed association of ST3 with a healthy gut microbiota.

An epidemiological survey on was carried out enrolling a total of 2524 subjects referred to the Umberto I Academic Hospital in Rome, for the routine parasitological exams, during 2017-2018. The studied population included a sample of immunocompromised individuals ( = 130) followed at the same hospital. DNA sequencing of the small subunit rRNA gene (SSU rDNA) locus was performed on samples positive to the coproparasitological analysis to molecular characterize the subtypes. Microscopical analysis detected in 192/2524 (7.6%) of the enrolled subjects. It was the organism most frequently identified in the analysed faecal samples diagnosed in single infection (5.6%) or in co-infection with other enteric protozoa (2%). Furthermore, it was found mainly in immunocompromised patients (22.3%) compared to immunocompetent ones (6.8%). As expected, ST3 was the most occurring subtype identified in 40% of the subjects, followed by ST1 (29%), ST2 (16%), ST4 (12%), and ST7 (3%). Next-generation sequencing (NGS) of the 16S rDNA was performed on a sub-sample of -ST3-carriers, homogenous by age and gender, as well as on -free subjects, to profile and compare their gut bacterial composition. A higher bacterial diversity was found in ST3-carriers, which exhibited a high abundance of , and while, a high percentage of was found in -free subjects. This study evidenced the presence of in 7.6% of faecal samples in Italy and a high circulation of the protist among immunocompromised patients (22.3%). Molecular characterization of positive samples evidenced the occurrence of five different subtypes, including zoonotic ST such as the ST7, highlighting the risk of transmission from animals. Study of the gut microbiota composition confirms previous evidences according to which, the colonisation by would be linked with an eubiotic gut characterized by potentially beneficial species such as and , rather than with a dysbiotic state, with a high abundance of Enterobacteriaceae, and corroborated the role of the protist as "an old friend" of the human gut.