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Plaque assay of rickettsiae in a mammalian cell line
Abstract:
Clear-cut and repeatable plaque assays were obtained for three rickettsiae of the spotted fever group (Rickettsia rickettsi, R. conori, and R. montana) in Vero cells used in a manner similar to that for arboviruses. In addition, three typhus group agents (R. typhi, R. canada, R. prowazeki) induced plaques in these cells. In preliminary tests Coxiella burneti (Nine Mile strain) failed to produce plaques. Comparable results were obtained in plastic flasks and plastic culture trays incubated in ambient air with or without addition of N-2-hydroxyethyl-piperazine-N'-2-ethanesulfinic acid buffer. Larger and more well defined R. rickettsi plaques were produced when cultures were overlaid with Leibovitz (L15) medium than with either medium 199 or Eagle medium. Phosphate-buffered saline containing bovine plasma albumin (fraction V), in contrast to brain heart infusion broth, as a diluent for preparing inocula consistently permitted development of larger and more numerous plaques with three agents: R. rickettsi, R. conori, and R. montana. When R. rickettsi and R. typhi were assayed in parallel in primary chicken embryo cultures and Vero cells, comparable results were obtained, but with R. canada results in Vero cells were superior. In contrast, R. prowazeki produced inconsistent results in Vero cells.
Insights
Vero cells enable reliable plaque assays for spotted fever and typhus group Rickettsiae. Optimizing media and diluents enhances plaque formation for improved Rickettsial detection.
Area of Science:
- Microbiology
- Cell Biology
- Virology
Background:
- Rickettsiae are obligate intracellular bacteria responsible for significant human diseases.
- Traditional methods for Rickettsial quantification can be laborious and time-consuming.
- Development of efficient plaque assay methods is crucial for Rickettsial research.
Purpose of the Study:
- To establish and optimize a plaque assay for Rickettsia species using Vero cells.
- To compare the efficacy of different cell culture media and diluents for Rickettsial plaque formation.
- To evaluate the suitability of Vero cells for assaying various Rickettsia groups.
Main Methods:
- Vero cells were utilized for plaque assays, adapting arbovirus techniques.
- Different cell culture media (Leibovitz L15, Medium 199, Eagle medium) and diluents (phosphate-buffered saline with bovine plasma albumin, brain heart infusion broth) were tested.
- Plaque formation was assessed for spotted fever group (Rickettsia rickettsi, R. conori, R. montana) and typhus group (R. typhi, R. canada, R. prowazeki) agents, as well as Coxiella burnetii.
Main Results:
- Clear and repeatable plaque assays were achieved for spotted fever group Rickettsiae and typhus group agents (R. typhi, R. canada) in Vero cells.
- Leibovitz (L15) medium and phosphate-buffered saline with bovine plasma albumin as a diluent promoted larger and more defined plaques.
- Vero cells showed superior results for R. canada compared to chicken embryo cultures, while R. prowazeki yielded inconsistent results.
Conclusions:
- Vero cells provide a robust platform for plaque assays of diverse Rickettsia species.
- Optimized conditions using specific media and diluents significantly improve plaque assay sensitivity and clarity.
- This plaque assay method offers a valuable tool for Rickettsial research and diagnostics.