Devon Willis | ALES Graduate Seminar

Event details:  A graduate exam seminar is a presentation of the student’s final research project for their degree.

This is an ALES MSc Final Exam Seminar by Devon Willis.  This seminar is open to the general public to attend.

Thesis Topic:

Effect of Preservatives on Growth and Filamentation of Listeria monocytogenes on Ready-to-Eat Meats

Seminar Abstract:

Listeria monocytogenes is a foodborne pathogen known to contaminate RTE foods and grow at refrigeration temperatures. It is also known to form filaments when stressed, which may affect monitoring and compromise consumer safety. The objective of this study was to observe the growth and morphological changes in L. monocytogenes grown on RTE hams with multiple preservative treatments and stored at refrigeration temperatures.

Two strains were inoculated onto hams treated with sodium lactate (1.4% w/w) and sodium diacetate (0.1% w/w), chitosan (0.5% v/w added as a solution in 1% acetic acid), partially purified bacteriocins (25.6 activity units/g) from Carnobacterium maltaromaticum UAL307, and combinations of sodium lactate and sodium diacetate or chitosan with the partially purified bacteriocins. Inoculated hams were stored at 4°C for up to 120 d. Growth characteristics were determined by plating on PALCAM agar, while filamentation was assessed by imaging flow cytometry.

Plate counts indicated that only a combination of sodium lactate and sodium diacetate with bacteriocins caused a significant decrease in growth of L. monocytogenes on the hams compared to the other treatments. Imaging flow cytometry found that the proportion of the bacterial population that filamented was significantly lower on hams treated with chitosan, either with or without bacteriocins present.

These results show that different preservatives have differing effects on L. monocytogenes, which may affect how these preservatives are applied and how this pathogen is regulated on RTE foods.