The effects of time and temperature on flow cytometry enumerated live Cryptosporidium parvum oocysts.

AIMS

Recoveries of spiked standard suspensions are used to evaluate method performance. For many applications, gamma-irradiated Cryptosporidium oocysts are appropriate. In contrast, methods that determine viability, such as Cryptosporidium cell culture, require the use of live oocysts. Oocyst standards are usually prepared at a flow cytometry laboratory for use at another laboratory, and thus the samples are shipped. The goal of this study was to evaluate the shipping and storage stability of flow cytometry enumerated live oocysts over time at three temperatures: 4 degrees C, room temperature and 37 degrees C.

METHODS AND RESULTS

Replicate samples containing 100 live C. parvum oocysts were prepared by flow cytometry and stored at 4 degrees C, room temperature and 37 degrees C. These samples were counted at various time points. Significant oocyst losses were observed after storage for 1 day at 37 degrees C, 7 days at room temperature and 21 days at 4 degrees C.

CONCLUSIONS

Live C. parvum oocysts internal standards should be used within 10 days of preparation, and stored and shipped at 4 degrees C.

SIGNIFICANCE AND IMPACT OF THE STUDY

When evaluating method performance with live oocysts, both the storage temperature and time are critical factors for obtaining reliable and accurate results.