Multilocus sequence typing of Dientamoeba fragilis identified a major clone with widespread geographical distribution

Abstract

The flagellated protozoan Dientamoeba fragilis is often detected in humans with gastrointestinal symptoms, but it is also commonly found in healthy subjects. As for other intestinal protozoa, the hypothesis that genetically dissimilar parasite isolates differ in their ability to cause symptoms has also been raised for D. fragilis. To date, only two D. fragilis genotypes (1 and 2) have been described, of which genotype 1 largely predominates worldwide. However, very few markers are available for genotyping studies and therefore the extent of genetic variation among isolates remains largely unknown. Here, we performed metagenomics experiments on two D. fragilis-positive stool samples, and identified a number of candidate markers based on sequence similarity to the phylogenetically related species Trichomonas vaginalis. Markers corresponding to structural genes and to genes encoding for proteases were selected for this study, and PCR experiments confirmed their belonging to the D. fragilis genome; two previously described markers (small subunit ribosomal DNA and large subunit of RNA polymerase II) were also included. Using this panel of markers, 111 isolates of human origin were genotyped, all of which, except one, belonged to genotype 1. These isolates had been collected at different times from symptomatic and asymptomatic persons of different age groups in Italy, Denmark, Brazil and Australia. By sequencing approximately 160kb from 500 PCR products, a very low level of polymorphism was observed across all the investigated loci, suggesting the existence of a major clone of D. fragilis with a widespread geographical distribution.

Dientamoeba fragilis diagnosis by fecal screening: relative effectiveness of traditional techniques and molecular methods

“…AY730405.1 and FJ649228.1). These results indicated low level of polymorphism, in agreement with recent studies [47,49].…”

Human intestinal parasites in Mahajanga, Madagascar: The kingdom of the protozoa

“…fragilis , G1 and G2, have been described [ 30 ]. This low genetic diversity has been recently confirmed by multilocus sequence typing of isolates from different regions of the world [ 37 ]. This study showed the worldwide predominance of G1 and the relative rarity of G2.…”

A clinical guideline onDientamoeba fragilisinfections

“…Due to the presence of specific virulence factors, ETEC, EIEC, EAEC and EHEC are all being recognized as pathogenic diarrhoea-causing variants of the generally harmless human commensal E. coli (Hart et al ., 1989; Robins-Browne and Hartland, 2002). Based on 18S rRNA sequence differences, two major D. fragilis genotypes have been described, but the overall significance with regard to pathogenicity (if any) is unclear (Johnson and Clark, 2000; Peek et al ., 2004; Windsor et al ., 2006; Hussein et al ., 2009; Dunwell, 2013; Cacciò et al ., 2016). Barratt et al detected the presence of RNA and coding genes in the transcriptome of D. fragilis known to be possible cytotoxic virulence factors such as cysteine peptidases, saposin-like proteins and a leukotriene A4 hydrolase-like peptidase, pointing to a pathogenic character of D. fragilis (Barratt et al ., 2015).…”