RESUMO
Blastocystis is one of the most frequent protozoa in human faecal samples, however, little is known about its relation with obesity. The present study aimed to analyse Blastocystis infection and subtypes in three adult populations classified according to body mass index (BMI). Faecal samples from 346 individuals were classified according to BMI: control (124 cases), overweight (110 cases), and obese (112 cases). Nucleic acid extraction from the samples was followed by amplification of partial 18S ribosomal RNA (18S rRNA) gene of Blastocystis. The neighbourjoining method was used to construct a phylogenetic tree from evolutionary distance data. Clinical findings were compared between Blastocystis infected and non-infected cases. Blastocystis was detected in 52 (15%) of 346 individuals with PCR assay. Blastocystis was less frequent in obese group (8%) than both control group (18.2%) and overweight group (18.5%). Subtype distribution was as follows: ST3 (n=21; 43.8%), ST2 (n=15; 31.3%), ST1 (n=10; 20.8%) and ST7 (n=2; 4.2%). The overall nucleotide diversity of 18S ribosomal RNA gene was 0.049. None of the gastrointestinal symptoms and gender was not significantly related with the infection. Despite the cross sectional nature of the study including a specific population, it suggests a negative association between Blastocystis infection and obesity. In addition, the lack of significant relation further supports asymptomatic colonization of Blastocystis.