Subtype analysis of Blastocystis isolates in Swedish patients
ABSTRACT Blastocystis is a genetically diverse and widespread intestinal parasite of animals and humans with controversial pathogenic potential. At least nine subtypes of Blastocystis have been found in humans. The genetic diversity of Blastocystis was examined in stool samples from 68 patients from the Stockholm area, Sweden. Blastocystis was identified by light microscopy, and subtyped by sequencing the 5'-end of the small subunit ribosomal RNA gene. Five Blastocystis subtypes were identified in the 63 patients whose samples were successfully subtyped: ST1 (15.9%), ST2 (14.3%), ST3 (47.6%), ST4 (20.6%), and ST7 (1.6%). ST3 was more common in males compared to females (P=0.049). Comparative molecular analysis of Blastocystis sequences revealed intra-subtype variations within the identified subtypes with the exception of ST4. Among ST4 sequences in this study, as well as in the majority of human GenBank sequences, a limited genetic diversity was found compared to what was found among the other common subtypes (ST1, ST2 and ST3). The relative prevalence of ST4 in this study was comparable to the overall distribution of ST4 in European cohorts (16.5%). This contrasts with the sparse reports of ST4 in studies from other continents, which may indicate that the distribution of this subtype is geographically heterogeneous.
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ABSTRACT: Blastocystis is a common single-celled parasite of humans and other animals comprising at least 13 genetically distinct small subunit ribosomal RNA lineages (subtypes (STs)). In this study we investigated intra-subtype genetic diversity and host specificity of two of the most common subtypes in humans, namely ST3 and ST4, by analysing and comparing over 400 complete and partial nuclear SSU-rDNAs and data from multilocus sequence typing (MLST) of the mitochondrion-like organelle (MLO) genome of 132 samples. Inferences from phylogenetic analyses of nuclear SSU-rDNA and concatenated MLST sequences were compatible. Human ST3 infections were restricted to one of four identified MLO clades except where exposure to non-human primates had occurred. This suggests relatively high host specificity within ST3, that human ST3 infections are caused predominantly by human-to-human transmission, and that human strains falling into other clades are almost certainly the result of zoonotic transmission. ST4 from humans belonged almost exclusively to one of two SSU-rDNA clades, and only five MLST sequence types were found among 50 ST4s belonging to Clade 1 (discriminatory index: 0.41) compared to 58 MLST sequence types among 81 ST3s (discriminatory index: 0.99). The remarkable differences in intra-subtype genetic variability suggest that ST4 has a more recent history of colonising humans than ST3. This is congruent with the apparently restricted geographical distribution of ST4 relative to ST3. The implications of this observation are unclear, however, and the population structure and distribution of ST4 should be subject to further scrutiny in view of the fact ST4 is being increasingly linked with intestinal disease.Infection, genetics and evolution: journal of molecular epidemiology and evolutionary genetics in infectious diseases 11/2011; 12(2):263-73. DOI:10.1016/j.meegid.2011.11.002 · 3.26 Impact Factor
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ABSTRACT: Blastocystis is one of the most common enteric parasites present in humans. There is still much uncertainty about the pathogenic potential of this parasite, and it was suggested that its pathogenicity could be subtype-related. This report aimed to study 98 Blastocystis isolates found in human stool specimens to identify the subtypes present and carry out phylogenetic analysis on these isolates. This study also aimed to show the relationship between subtype and symptoms. Five-hundred and thirteen stool samples were submitted to five different diagnostic techniques for the detection of Blastocystis. Polymerase chain reaction (PCR)-positive samples were then sequenced and the small subunit (SSU) rDNA sequences were aligned and submitted to phylogenetic analysis. Ninety-eight samples were positive by any of the diagnostic methods for Blastocystis and 96 were positive by PCR. There were seven different subtypes (1, 2, 3, 4, 6, 7 and 8) identified by PCR and sequencing. This is the first large-scale study to examine the occurrence of Blastocystis in Australia. This study reports the high incidence of subtype 3 (44 %) in this population and discusses the emerging idea of subtype-dependent pathogenicity.European Journal of Clinical Microbiology 09/2012; 32(3). DOI:10.1007/s10096-012-1746-z · 2.67 Impact Factor
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ABSTRACT: Blastocystis is the most common non-fungal micro-eukaryote of the human intestinal tract and comprises numerous subtypes (STs), nine of which have been found in humans (ST1-ST9). While efforts continue to explore the relationship between human health status and subtypes, no consensus regarding subtyping methodology exists. It has been speculated that differences detected in subtype distribution in various cohorts may to some extent reflect different approaches. Blastocystis subtypes have been determined primarily in one of two ways: 1) sequencing of small subunit ribosomal RNA gene (SSU-rDNA) PCR products and 2) PCR with subtype-specific sequence-tagged site (STS) diagnostic primers.Here, STS primers were evaluated against a panel of samples (n=58) already subtyped by SSU-rDNA sequencing (barcode region), including subtypes for which STS primers are not available, and a small panel of DNAs from 4 other eukaryotes often present in faeces (n=18). While STS primers appeared highly specific, their sensitivity was only moderate, and our results indicate that some infections may go undetected when this method is used. False-negative STS results were not linked exclusively to certain subtypes or alleles and evidence of substantial genetic variation in STS loci was obtained. Since the majority of DNAs included in the study were extracted from faeces, it is possible that STS primers may generally work better with DNAs extracted from Blastocystis cultures. In conclusion, due to its higher applicability and sensitivity, and since sequence information is useful for other forms of research, SSU-rDNA barcoding is recommended as the method of choice for Blastocystis subtyping.Journal of clinical microbiology 10/2012; 51(1). DOI:10.1128/JCM.02541-12 · 4.23 Impact Factor