Heterogeneidad genética de blastocystis hominisimplicaciones patogénicas.

Abstract

Blastocystis hominis is the most prevalent specie of intestinal protozoa found in men of uncertain role in human disease. This study was undertaken to examine the degree of criptic genetic variation within B. hominis detectable using riboprinting (restriction fragment length polymorphism analysis of polymerase chain reaction amplified small subunit rDNA); the analysis of multiple target sequences by a single set of polymerase chain reaction primers; and the existence of demes with different pathogenic potential after to analyse the enzyme activity. The small subunit ribosomal RNA genes of 51 isolates were amplified using standard polymerase chain reaction conditions and the primers RD5 y RD3 (Clark, CG; 1992). The amplification products were digested with 3 restriction enzymes (Hinf I, Rsa I, Alu I). We used a similar method by the primers F1 y R1 (Böhm-Gloning et al., 1997) and the same restriction endonuclease enzymes. Extensive sequence variation was discovered in B. hominis ribosomal RNA genes and the isolates grouped of at least five differents patterns or ribodemes. The ribodeme R2 was the most frequently isolated variant, is composed of isolates obtained from patients with acute diarrhea. The statistical association found between R2 and acute diarrhea in the absence of other enteropathogens suggest the pathogenic role of this ribodema. The results based on the amplification products obtaines by a single set of polymerase chain reaction primers TR7 y TR8 (Init et al., 1999) showed intrastrain variations among isolates, but this set of PCR primers only can be used in the detection of variable DNA repeat patterns in axenic cultures because the reaction is not selectivity for lower eukayotes, it is present in prokaryotes too . The enzyme polymorphism of this organism has been demostrated by enzyme electrophoresis of 31 axenic B. hominis isolates by electrophoresis on polyacrylamide gel under nondenaturating conditions (PAGE). Eight enzyme systems were studied: GOT (EC 2.6.1.1), GPI (EC 5.3.1.9), EM (EC 1.1.1.40), G6PDH (EC 1.1.1.49), 6PGDH (EC 1.1.1.44), MDH (EC 1.1.1.37), HK (EC 2.7.1.1), PGM (EC 2.7.5.1. ). The isolates showed an identical isoenzyme profile by the seven activities, in the case of MDH the presence of one band with different electrophoretic migrations detected the existence the two zimodemes. The description of different zymodemes confirms the heterogeneity of this organism. This study illustrates the need to reexamine the role of B. hominis in disease taking the genetic diversity of the parasite into account.