Recoverability of Listeria monocytogenes after coculture with Tetrahymena pyriformis

Authors: Meinersmann, Richard - Rick; Berrang, Mark; Rigsby, Luanne

Submitted to: Journal of Food Safety
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/27/2020
Publication Date: 2/16/2020
Citation: Meinersmann, R.J., Berrang, M.E., Rigsby, L.L. 2020. Recoverability of Listeria monocytogenes after coculture with Tetrahymena pyriformis. Journal of Food Safety. https://doi.org/10.1111/jfs.12778.
DOI: https://doi.org/10.1111/jfs.12778

Interpretive Summary: Listeria monocytogenes is a bacteria that lives in food processing habitats. The organism can contaminate the food product and become a health hazard. Protozoa that eat and destroy bacteria may provide a safe method of controlling Listeria, but protozoa tested to date have not been effective in killing Listeria. We tested a bacteria-eating protozoa known as Tetrahymena pyriformis for its ability to kill Listeria. The two organisms were cultured together and once the protozoa had ingested a share of the bacteria, the residual bacteria that were outside of the protozoa were killed with antibiotic and the time it took the Tetrahymena to kill the Listeria that had been ingested was measured. Almost all the ingested Listeria were killed within 24 hours. Nineteen different strains of Listeria were tested and all were equally killed. The Tetrahymena showed ability to kill adherent Listeria as well as those in culture suspension. Thus, Tetrahymena may be a useful candidate for treating food processing plants to control Listeria.

Technical Abstract: Bactivory by protozoa is a major factor that limits the number of bacteria in nature and may control the presence of Listeria monocytogenes. The effectiveness of Tetrahymena pyriformis destruction of L. monocytogenes was measured. Within one hour, 35 to 40 T. pyriformis cells ingested an average of 1219 CFU of L. monocytogenes. Gentamicin was then added to kill un-ingested Listeria. In 24 hours the recoverable bacteria were reduced at an exponential rate to undetectable levels (<1 per culture). A genetically diverse set of L. monocytogenes cultures all reduced Listeria recovery by the same degree. In assays without addition of gentamicin, numbers of attached L. monocytogenes cells were lessened from an average of log 6.5 CFU/2 ml culture to log 4.7 CFU/2 ml culture. T. pyriformis was capable of lowering numbers of both free-swimming and attached L. monocytogenes. This technology may have applications to control L. monocytogenes in food processing environments.