ORIGINAL ARTICLE

Do Toxoplasma gondii RH strain tachyzoites evolve during continuous passage?

S Mavin¹, A W L Joss¹, J Ball² and D O Ho-Yen¹

¹ Scottish Toxoplasma Reference Laboratory, Raigmore Hospital, Inverness IV2 3UJ, UK
² Division of Microbiology and Infectious Diseases, University of Nottingham, Queens’ Medical Centre, Nottingham NG7 2UH, UK

Correspondence to:
Correspondence to:
Dr S Mavin
Scottish Toxoplasma Reference Laboratory, Raigmore Hospital, Inverness IV2 3UJ, UK; microbiology{at}haht.scot.nhs.uk

Aim: To examine three lineages of Toxoplasma gondii RH strain in terms of performance in the dye test, culture, and gene expression.

Methods: Historical data (culture growth and performance in the dye test) from three lineages of RH strain tachyzoites (B, J, and Q) that had been continuously cultured in HeLa cells was assessed. Tachyzoite harvests obtained during continuous cell culture were retrieved from liquid nitrogen and cultured in HeLa cells, providing mRNA that was extracted and used to study gene expression using random amplified polymorphic DNA analysis at different stages of lineage adaptation to continuous culture.

Results: The B and Q lineages consistently produced tachyzoites that were successfully used in the dye test and their gene expression was stable after multiple passages. The J lineage had unpredictable growth, tachyzoites unsuitable for use in the dye test, and changing gene expression with multiple passage.

Conclusion: This study has explained some anomalies in the performance of different stocks of T gondii, and suggests that lineages that are still evolving in cell culture should be avoided.

Keywords: random amplified polymorphic DNA analysis; RH strain; Toxoplasma gondii; continuous cell culture; gene expression

Abbreviations: PCR, polymerase chain reaction; RAPD, random amplified polymorphic DNA; TBE, Tris borate EDTA

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