Short communication: Long-term −20°C survival of Listeria monocytogenes in artificially and process-contaminated ice cream involved in an outbreak of listeriosis

Abstract

Listeria monocytogenes was linked to an outbreak of foodborne illness associated with in-process contaminated ice cream in the United States from 2010 to 2015 that sickened 10 individuals and led to 3 deaths. Ice cream obtained from the outbreak was used in this study to examine the population dynamics of L. monocytogenes as in-process contaminants compared with artificially inoculated cells. Because challenge studies of food products generally use artificial contamination, it is necessary to understand the differences in survival, if any, between these 2 types of contaminants. We hypothesized that laboratory-grown cultures of the pathogen that were not exposed to the environmental stresses of the manufacturing facility would show different population dynamics in an ice cream challenge study compared with in-process contaminants. In this study, half of the outbreak-associated ice cream samples were artificially inoculated with a 10 cfu/g cocktail of L. monocytogenes; the other half contained only the in-process contaminants. All samples were stored at −20°C and tested for pathogen levels (n = 10 for each contaminant type at each time point) by the most probable number method at 3-mo intervals for 36 mo. Generally, population levels between the 2 contamination states in the ice cream were not significantly different and L. monocytogenes survived for at least 36 mo, regardless of contamination state. Overall, our results suggest that the use of L. monocytogenes as an artificial contaminant in challenge studies and risk assessment of ice cream during frozen storage give results similar to those shown by in-process contaminants.

Review of the prevalence of foodborne pathogens in milk and dairy products in Ethiopia

“…This information could provide insight into the potential sources of contamination, which could inform practices aimed at reducing the prevalence of L. monocytogenes in the ice cream supply chain. While L. monocytogenes is not able to grow at ice cream recommended storage temperature, it can survive freezing temperatures ( Salazar, Stewart, Shazer, & Tortorello, 2019 ) and presents a food safety risk. This has been demonstrated by outbreaks of L. monocytogenes in the USA that had been traced back to ice cream as a source of contamination ( Chen et al., 2016 , Rietberg et al., 2016 ).…”

Listeriosis during pregnancy: a retrospective cohort study

“…Similarly, in our study, more than half of pregnancy-associated listeriosis cases were occurred in summer (50.0%, 7/14). As L. monocytogenes was a psychrophilic organism, the ready-to-eat foods and foods stored at refrigeration temperatures are the main sources of L. monocytogenes [ 29 ]. And people have more opportunities to eat food that is inadequately cooked and improperly stored in the refrigerator during the warmer seasons.…”

Pregnancy-Associated Listeriosis in a Tertiary Hospital in Ningbo, Zhejiang, China: A Retrospective Study

“…Similarly, in our study, more than a half pregnancy-associated listeriosis cases were occurred in summer (50.0%, 7/14). As L. monocytogenes was a psychrophilic organism, the ready-to-eat foods and foods stored at refrigeration temperatures are the main sources of L. monocytogenes [29]. And people have more opportunity to eat food that is inadequately cooked and improperly stored in the refrigerator during the warmer seasons.…”