Abstract
Blastocystis spp is a common intestinal parasite of humans and animals that has been associated to the etiology of irritable bowel syndrome (IBS); however, some studies have not found this association. Furthermore, many biological features of Blastocystis are little known. The objective of present study was to assess the generation times of Blastocystis cultures, from IBS patients and from asymptomatic carriers. A total of 100 isolates were obtained from 50 IBS patients and from 50 asymptomatic carriers. Up to 50 mg of feces from each participant were cultured in Barret’s and in Pavlova’s media during 48 h. Initial and final parasitological load were measured by microscopy and by quantitative PCR. Amplicons were purified, sequenced and submitted to GenBank; sequences were analysed for genetic diversity and a Bayesian inference allowed identifying genetic subtypes (ST). Generation times for Blastocystis isolates in both media, based on microscopic measures and molecular assays, were calculated. The clinical symptoms of IBS patients and distribution of Blastocystis ST 1, 2 and 3 in both groups was comparable to previous reports. Interestingly, the group of cases showed scarce mean nucleotide diversity (π) as compared to the control group (0.011±0.016 and 0.118±0.177, respectively), whilst high gene flow and small genetic differentiation indexes between different ST were found. Besides, Tajima’s D test showed negative values for ST1-ST3. No statistical differences regarding parasitological load between cases and controls in both media, as searched by microscopy and by qPCR, were detected except that parasites grew faster in Barret’s than in Pavlova’s medium. Interestingly, slow growth of isolates recovered from cases in comparison to those of controls was observed (p<0.05). We propose that generation times of Blastocystis might be easily affected by intestinal environmental changes due to IBS probably because virulent strains with slow growth may be selected, reducing their genetic variability.
Highlights
Irritable bowel syndrome (IBS) is defined as a functional bowel disorder in which abdominal pain or discomfort is associated with disordered defecation or with a change in bowel habits in the absence of an organic cause [1,2]
Clinical symptoms in IBS patients infected with Blastocystis were concordant to those reported in Mexican populations [8, 38,39,40] and in other countries [6,7, 41,42,43]
Distribution of Blastocystis ST 1, 2 and 3 was comparable to other reports [8, 10, 38,39,40], showing no association with symptoms or the development of IBS, in contrast with those findings reported by Ramírez et al [44], who found that all patients infected with Blastocystis ST2 presented diarrhea, while than asymptomatic carriers exhibited only ST1
Summary
Irritable bowel syndrome (IBS) is defined as a functional bowel disorder in which abdominal pain or discomfort is associated with disordered defecation or with a change in bowel habits in the absence of an organic cause [1,2]. There are probably several interconnected factors which occur to varying degrees in patients that account for the clinical symptoms of IBS, these include altered gut reactivity (colonic and/or small bowel motility) in response to luminal or psychological stimuli, hypersensitive viscera or gut, enhanced visceral perception and pain [3,4]. Blastocystis spp., an intestinal parasite, is one of the most common parasites worldwide in humans and its ability to cause disease has been questioned, some reports have demonstrated that this microorganism is associated to the development of IBS [5,6,7,8,9]. The objective of present study was to assess generation times and genetic polymorphism of Blastocystis cultures from IBS patients and from asymptomatic carriers
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