Growth of <named-content content-type="genus-species">Listeria monocytogenes</named-content> within a Caramel-Coated Apple Microenvironment

ABSTRACT A 2014 multistate listeriosis outbreak was linked to consumption of caramel-coated apples, an unexpected and previously unreported vehicle for Listeria monocytogenes. This outbreak was unanticipated because both the pH of apples (<4.0) and the water activity of the caramel coating (<0...

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Autores principales:	Kathleen A. Glass, Max C. Golden, Brandon J. Wanless, Wendy Bedale, Charles Czuprynski
Formato:	article
Lenguaje:	EN
Publicado:	American Society for Microbiology 2015
Materias:	Microbiology QR1-502
Acceso en línea:	https://doaj.org/article/d9988d75db8343509b342528328a2290
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spelling	oai:doaj.org-article:d9988d75db8343509b342528328a22902021-11-15T15:41:31ZGrowth of <named-content content-type="genus-species">Listeria monocytogenes</named-content> within a Caramel-Coated Apple Microenvironment10.1128/mBio.01232-152150-7511https://doaj.org/article/d9988d75db8343509b342528328a22902015-10-01T00:00:00Zhttps://journals.asm.org/doi/10.1128/mBio.01232-15https://doaj.org/toc/2150-7511ABSTRACT A 2014 multistate listeriosis outbreak was linked to consumption of caramel-coated apples, an unexpected and previously unreported vehicle for Listeria monocytogenes. This outbreak was unanticipated because both the pH of apples (<4.0) and the water activity of the caramel coating (<0.80) are too low to support Listeria growth. In this study, Granny Smith apples were inoculated with approximately 4 log10 CFU of L. monocytogenes (a cocktail of serotype 4b strains associated with the outbreak) on each apple's skin, stem, and calyx. Half of the apples had sticks inserted into the core, while the remaining apples were left intact. Apples were dipped into hot caramel and stored at either 7°C or 25°C for up to 11 or 28 days, respectively. Data revealed that apples with inserted sticks supported significantly more L. monocytogenes growth than apples without sticks under both storage conditions. Within 3 days at 25°C, L. monocytogenes populations increased >3 log10 in apples with sticks, whereas only a 1-log10 increase was observed even after 1 week for caramel-coated apples without sticks. When stored at 7°C, apples with sticks exhibited an approximately 1.5-log10 increase in L. monocytogenes levels at 28 days, whereas no growth was observed in apples without sticks. We infer that insertion of a stick into the apple accelerates the transfer of juice from the interior of the apple to its surface, creating a microenvironment at the apple-caramel interface where L. monocytogenes can rapidly grow to levels sufficient to cause disease when stored at room temperature. IMPORTANCE Neither caramel nor apples are a food where the pathogenic bacterium Listeria monocytogenes should grow, as caramel does not contain enough free water and apples are too acidic. Caramel-coated apples, however, were recently linked to a deadly outbreak of listeriosis. We hypothesized that inserting a stick into the apple releases juice to the interface between the apple and caramel, providing a more hospitable environment than either component alone. To test this hypothesis, apples were inoculated with L. monocytogenes prior to caramel dipping. Some apples had sticks inserted into them before dipping, while others did not. No growth of L. monocytogenes occurred on refrigerated caramel apples without sticks, whereas slow growth was observed on refrigerated caramel apples with sticks. In contrast, significant pathogen growth was observed within 3 days at room temperature on caramel apples with sticks inserted. Food producers should consider interfaces between components within foods as potential niches for pathogen growth.Kathleen A. GlassMax C. GoldenBrandon J. WanlessWendy BedaleCharles CzuprynskiAmerican Society for MicrobiologyarticleMicrobiologyQR1-502ENmBio, Vol 6, Iss 5 (2015)
institution	DOAJ
collection	DOAJ
language	EN
topic	Microbiology QR1-502
spellingShingle	Microbiology QR1-502 Kathleen A. Glass Max C. Golden Brandon J. Wanless Wendy Bedale Charles Czuprynski Growth of <named-content content-type="genus-species">Listeria monocytogenes</named-content> within a Caramel-Coated Apple Microenvironment
description	ABSTRACT A 2014 multistate listeriosis outbreak was linked to consumption of caramel-coated apples, an unexpected and previously unreported vehicle for Listeria monocytogenes. This outbreak was unanticipated because both the pH of apples (<4.0) and the water activity of the caramel coating (<0.80) are too low to support Listeria growth. In this study, Granny Smith apples were inoculated with approximately 4 log10 CFU of L. monocytogenes (a cocktail of serotype 4b strains associated with the outbreak) on each apple's skin, stem, and calyx. Half of the apples had sticks inserted into the core, while the remaining apples were left intact. Apples were dipped into hot caramel and stored at either 7°C or 25°C for up to 11 or 28 days, respectively. Data revealed that apples with inserted sticks supported significantly more L. monocytogenes growth than apples without sticks under both storage conditions. Within 3 days at 25°C, L. monocytogenes populations increased >3 log10 in apples with sticks, whereas only a 1-log10 increase was observed even after 1 week for caramel-coated apples without sticks. When stored at 7°C, apples with sticks exhibited an approximately 1.5-log10 increase in L. monocytogenes levels at 28 days, whereas no growth was observed in apples without sticks. We infer that insertion of a stick into the apple accelerates the transfer of juice from the interior of the apple to its surface, creating a microenvironment at the apple-caramel interface where L. monocytogenes can rapidly grow to levels sufficient to cause disease when stored at room temperature. IMPORTANCE Neither caramel nor apples are a food where the pathogenic bacterium Listeria monocytogenes should grow, as caramel does not contain enough free water and apples are too acidic. Caramel-coated apples, however, were recently linked to a deadly outbreak of listeriosis. We hypothesized that inserting a stick into the apple releases juice to the interface between the apple and caramel, providing a more hospitable environment than either component alone. To test this hypothesis, apples were inoculated with L. monocytogenes prior to caramel dipping. Some apples had sticks inserted into them before dipping, while others did not. No growth of L. monocytogenes occurred on refrigerated caramel apples without sticks, whereas slow growth was observed on refrigerated caramel apples with sticks. In contrast, significant pathogen growth was observed within 3 days at room temperature on caramel apples with sticks inserted. Food producers should consider interfaces between components within foods as potential niches for pathogen growth.
format	article
author	Kathleen A. Glass Max C. Golden Brandon J. Wanless Wendy Bedale Charles Czuprynski
author_facet	Kathleen A. Glass Max C. Golden Brandon J. Wanless Wendy Bedale Charles Czuprynski
author_sort	Kathleen A. Glass
title	Growth of <named-content content-type="genus-species">Listeria monocytogenes</named-content> within a Caramel-Coated Apple Microenvironment
title_short	Growth of <named-content content-type="genus-species">Listeria monocytogenes</named-content> within a Caramel-Coated Apple Microenvironment
title_full	Growth of <named-content content-type="genus-species">Listeria monocytogenes</named-content> within a Caramel-Coated Apple Microenvironment
title_fullStr	Growth of <named-content content-type="genus-species">Listeria monocytogenes</named-content> within a Caramel-Coated Apple Microenvironment
title_full_unstemmed	Growth of <named-content content-type="genus-species">Listeria monocytogenes</named-content> within a Caramel-Coated Apple Microenvironment
title_sort	growth of <named-content content-type="genus-species">listeria monocytogenes</named-content> within a caramel-coated apple microenvironment
publisher	American Society for Microbiology
publishDate	2015
url	https://doaj.org/article/d9988d75db8343509b342528328a2290
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Growth of <named-content content-type="genus-species">Listeria monocytogenes</named-content> within a Caramel-Coated Apple Microenvironment

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