Liquid Media Found Practical for Diarrheagenic Parasite

A common protozoan in the human intestinal tract that can cause the so-called blastocystosis characterized by diarrhea, can be grown in liquid culture media.

In vitro culture methods could be safe alternatives to identify Blastocystis hominis for both clinical diagnosis and field study purposes, as present methods are potentially toxic to laboratory personnel.

Scientists at Xi’an Jiaotong University (China) isolated eight samples of B. hominis from symptomatic patient fresh stool samples. More than five B. hominis cells were seen per high-power magnification field. To determine whether in vitro culture could be an environmentally safe alternative, the culture growth of B. hominis observed and compared in three commercially available liquid media: Roswell Park Memorial Institute (RPMI) 1640, 199 Medium, and Dulbecco's modified Eagle's medium (DMEM). The sensitivity and specificity of these culture methods to identify B. hominis were compared with those of existing methods used clinically.

The anaerobic culture of B. hominis in these media required a total inoculum sizes of no less than 105 cells; pH values ranging from 7.0 to 7.5; concentrations of calf or horse serum ranging from 10% to 30%; and basic antibiotics have to be added. Growth peaking times were at days 3, 6, and 9 at pH 7.5 or days 4 and 8 or 9 at pH 7.0 at 37 °C. No significant differences were noted in multiplication or generation times for the cultivation of B. hominis. In 56 of 398 positive cases, the short-term in vitro culture method achieved the best performance with regard to sensitivity and specificity of the five methods studied. All three culture media were from the Gibco (Carlsbad, CA, USA) range of culture media. B. hominis identification has depended on the discovery of vacuolar, granular, amoebic, or cystic forms in stool samples using wet mount smears, iodine staining, trichrome staining, or iron hematoxylin staining.

The authors concluded that the in vitro culture method had the advantage of environmental safety, convenience in preparation and storage, facility in morphologic discrimination, and outstanding performance in terms of sensitivity and specificity, and could be applied to identify B. hominis for clinical diagnosis except in emergency situations. Prevalence surveys in China suggest that about 6% of patients with diarrhea have blastocystosis. The study was published on November 11, 2011, in the International Journal of Infectious Diseases.

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