Stage-Specific, Fluorescent Toxoplasma gondii

The genome of Toxoplasma gondii, the causal agent of toxoplasmosis, is readily amenable to genetic manipulation in the laboratory making it an ideal model system to study the basic biology of parasitism, such as its complex life cycle. The life cycle stages of T. gondii include sporozoites, merozoites, tachyzoites, and bradyzoites. The factors involving the stage conversion of invading tachyzoites to the bradyzoite stage contained within dormant tissue cysts and the mechanisms of cyst reactivation are not fully understood.

Recent additions to the BEI Resources protozoan catalog include two fluorescent, stage-specific, transgenic T. gondii reporter strains derived from the recombinant type I/III strain EGS, which is able to spontaneously form cysts in vitro.1,2,3,4 Transfection of strain EGS with plasmids expressing fluorescent tags under the control of stage-specific promoters resulted in two strains, T. gondii, strain EGS SAG1-mCherry LDH2-sfGFP (NR-53930) and T. gondii, strain EGS SAG1-mCherry LDH2-sfGFP MSF-BFP (NR-53931), that allow for monitoring of parasite stage conversion both in vitro and in vivo.5,6

NR-53930 expresses the red fluorescent protein mCherry and superfolder green fluorescent protein (sfGFP), with parasites in the bradyzoite stage positive for sfGFP and negative for mCherry; parasites in the tachyzoite stage of the life cycle are positive for mCherry and negative for sfGFP. NR-53931 has the addition of blue fluorescent protein (BFP), with merozoite-stage parasites positive for BFP and negative for sfGFP and mCherry.6

For more information on these strains, including specific culture conditions to induce stage conversion, please refer to the individual product documentation available on the BEI Resources website.


BEI Resources 

Poduct Description


Toxoplasma gondii, strain EGS SAG1-mCherry LDH2-sfGFP


Toxoplasma gondii, strain EGS SAG1-mCherry LDH2-sfGFP MSF-BFP








  1. Vidigal, P. V., et al. “Prenatal Toxoplasmosis Diagnosis from Amniotic Fluid by PCR.” Rev. Soc. Bras. Med. Trop. 35 (2002): 1-6. PubMed: 11873253.
  2. Ferreira, A. M., et al. “Genetic Analysis of Natural Recombinant Brazilian Toxoplasma gondii Strains by Multilocus PCR-RFLP.” Infect. Genet. Evol. 6 (2006): 22-31. PubMed: 16376837.
  3. Ferriera, A. M., et al. “Virulence for BALB/c Mice and Antigenic Diversity of Eight Toxoplasma gondii Strains Isolated from Animals and Humans in Brazil.” Parasite 8 (2001): 99-105. PubMed: 11474987
  4. Paredes-Santos, T. C., et al. “Spontaneous Cystogenesis in vitro of a Brazilian Strain of Toxoplasma gondii.” Parasitol. Int. 62 (2013): 181-188. PubMed: 23269201.
  5. Paredes-Santos, T. C., et al. “Development of Dual Fluorescent Stage Specific Reporter Strains of Toxoplasma gondii to Follow Tachyzoite and Bradyzoite Development In Vitro and In Vivo.” Microbes Infect. 18 (2016): 39-47. PubMed: 26432517.
  6. Sinai, A. P., et al. “Bradyzoite and Sexual Stage Development.” In: L. M. Weiss and K. Kim, Toxoplasma gondii: The Model Apicomplexan - Perspectives and Methods (3rd ed.). Elsevier, 2020. 807-857.

Image:  Transmission electron micrograph of SARS-CoV-2 virus particles (NIAID/CC BY 2.0)

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