ORIGINAL PAPER Genetic variability of Blastocystis sp. isolates obtained from cancer and HIV/AIDS patients T. C. Tan & S. C. Ong & K. G. Suresh Received: 18 June 2009 / Accepted: 22 June 2009 / Published online: 15 July 2009 # Springer-Verlag 2009 Abstract This represents the first study to determine the genetic diversity of Blastocystis sp. among cancer and HIV/ AIDS patients. Forty Blastocystis sp. isolates obtained from 20 cancer and 20 HIV/AIDS patients were genotyped by PCR using seven pairs of known sequenced-tagged site primers. Out of the 40 isolates, 38 were identified as one of the known genotypes and two isolates were negative with all the STS primers. Blastocystis sp. subtype 3 which is reported to be associated with disease was found to be predominant among the study subjects. Introduction Blastocystis sp. is a highly polymorphic organism with various morphological forms being reported in the literature including vacuolar, granular, amoeboid, cyst, avacuolar, and multivacuolar forms (Stenzel and Boreham 1996; Tan et al. 2002). Despite the unresolved controversy over its pathogenicity, Blastocystis sp. remains one of the most common intestinal parasites in humans (Stenzel and Boreham 1996). Prevalence of up to 10% and 50% was reported from developed and developing countries, respec- tively (Stenzel and Boreham 1996). Studies have shown the extensive genetic diversity of the organism in both humans and animals (Yoshikawa et al. 1996, 2004; Böhm-Gloning et al. 1997; Clark 1997; Abe 2004; Noël et al. 2005). Due to its low host specificity, a consensus has been reached to name the organism as Blastocystis sp. subtype 1 to 10 (ST1 to ST10) (Stensvold et al. 2007). Molecular epidemiological studies in various countries such as Japan, the Philippines, China, Pakistan, Thailand, Germany, Bangladesh, and UK, Turkey, France, and Spain revealed a worldwide distribution of the genotypes (Clark 1997; Böhm-Gloning et al. 1997; Yoshikawa et al. 2004; Yan et al. 2006; Li et al. 2007; Rivera 2008; Ozyurt et al. 2008; Souppart et al. 2009; Domínguez-Márquez et al. 2009). Blastocystis hominis has increasingly been implicated for diarrheal illness in immunocompromised individuals (Tan et al. 2002). Prevalence studies of Blastocystis in immunocompromised individuals have been confined to HIV/AIDS patients and there is general lack of informa- tion on the prevalence of the organism in other immuno- compromised individuals such as cancer patients. The purpose of this study is to determine the prevalence of Blastocystis sp. in both cancer and HIV/AIDS patients so as to determine whether a particular genotype is predom- inant. This represents the first study to determine the genetic diversity of Blastocystis sp. among cancer and HIV/AIDS individuals in Malaysia by PCR with the seven pairs of sequenced-tagged site (STS) primers reported by Yoshikawa et al. (2004). Materials and methods Sample collection and culture of Blastocystis sp. isolates A total of 311 cancer patients and 247 HIV-infected individuals attended to local hospitals were examined for Blastocystis sp. infection. The parasites were isolated from patients’ fecal sample by in vitro cultivation at 37°C using Jones’ medium (Jones 1946) supplemented with 10% horse serum (Tan et al. 2008). Subsequently, after isolation, the T. C. Tan : S. C. Ong : K. G. Suresh (*) Department of Parasitology, Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia e-mail: suresh@um.edu.my Parasitol Res (2009) 105:1283–1286 DOI 10.1007/s00436-009-1551-5