Listeria monocytogenes loss of cultivability on carrot is associated with the formation of mesosome-like structures

Authors: BOLTEN, SAMANTHA - Oak Ridge Institute For Science And Education (ORISE); Mowery, Joseph; Gu, Ganyu; REDDING, MARINA - Oak Ridge Institute For Science And Education (ORISE); KROFT, BRENDA - University Of Maryland; Luo, Yaguang - Sunny; Nou, Xiangwu

Submitted to: International Journal of Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/2/2023
Publication Date: 2/8/2023
Citation: Bolten, S., Mowery, J.D., Gu, G., Redding, M., Kroft, B., Luo, Y., Nou, X. 2023. Listeria monocytogenes loss of cultivability on carrot is associated with the formation of mesosome-like structures. International Journal of Food Microbiology. https://doi.org/10.1016/j.ijfoodmicro.2023.110121.
DOI: https://doi.org/10.1016/j.ijfoodmicro.2023.110121

Interpretive Summary: Carrot is an agricultural commodity that shows antimicrobial activity against foodborne pathogen Listeria monocytogenes but the underlying mechanism of action is not well known. In this study, ARS scientists examined this carrot antilisterial activity and determined that several Listeria species were equally susceptible to exposure to fresh-cut carrots. On cut carrot surface, Listeria monocytogenes seemed to quickly loss ability to grow but cell membranes seemed remained intact. This loss of cultivability is associated with formation of mesosome-like structures in Listeria monocytogenes. This finding is useful for better understanding carrot antilisterial activity and the survival of Listeria in fresh produce.

Technical Abstract: Raw carrot is known to have antimicrobial activity against Listeria monocytogenes, but the mechanism of action has not been fully elucidated. In this study, we examined carrot antilisterial activity against several strains of Listeria species (including L. grayi, L. innocua, L. seeligeri, and L. welshimeri) and L. monocytogenes. A representative strain of L. monocytogenes was subsequently used for further characterizing carrot antilisterial activity. Exposure to fresh-cut carrot for 15 min resulted in similar loss of cultivability, ranging from 2.5 to 4.7 log, across all Listeria strains evaluated. However, different fresh-cut carrots showed varying antilisterial potency. L. monocytogenes recovered from the fresh-cut surface of different raw carrots was 1.7 to 4.1 log lower than levels obtained from paired boiled carrot samples with abolished antilisterial activity. L. monocytogenes loss of cultivability following carrot exposure was 2.8 to 3.1 log higher when enumerated by culture-dependent methods than by culture-independent methods including PMAxx-qPCR, suggesting that carrot antilisterial activity was not associated with a loss of L. monocytogenes cell membrane integrity and putative cell viability. Transmission electron microscopy imaging revealed that L. monocytogenes rapidly formed mesosome-like structures upon exposure to carrot fresh-cut surface but not upon exposure to boiled carrot surface, suggesting an association between the formation of these mesosome-like structures and a loss of cultivability in L. monocytogenes.