Salmonella Typhimurium level in mealworm larvae after exposure to contaminated substrate

Annette Nygaard Jensen, Christine Johnsen, Sussie H. Hansen

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Abstract

Mealworms (Tenebrio molitor) for feed and food must be reared on feed-grade materials and findings of Salmonella spp. bacteria, which are important foodborne pathogens, have not yet been reported. However, Salmonella spp. belongs to the family of Enterobacteriaceae, which is found in levels up to 7.5 Log CFU/g in mealworms. This indicates that Salmonella spp. may be able to thrive in the mealworms if introduced into the production. This study aimed to assess the level of salmonella to be found in mealworms after exposure to different salmonella contamination levels in the substrate. The initial contamination level was 2, 4 or 6 Log CFU/g of a Salmonella enterica serotype Typhimurium strain resistant to rifampicin (in-house strain). Samples of mealworm and substrate were collected at start and additional four times until termination at day 7. For each sample, ten-fold dilutions series were prepared from 1 g of homogenized sample in 9 ml saline (0.9% NaCl). Each dilution was plated (0.1) on Nutrient Agar (NA) with rifampicin 50 mg/L to suppress competing bacteria, and incubated overnight at 37oC before counting of colonies. Presumptive S. Typhimuriumrif colonies were verified by slide-agglutination. Preliminary results indicated that the S. Typhimurium level found in mealworm and substrate depended on the initial contamination level while there was no clear effect over time (7 days). In future studies it would be of interest to see for how long salmonella will persist in the mealworms and the substrate after introduction. Also, the quantitative method is limited by a detection level of minimum 1 Log CFU/g and a qualitative approach with enrichment of the samples would be necessary to exclude the presence of salmonella in low numbers. Finally, the entire mealworm was homogenized and analyzed, not allowing concluding whether the salmonella had been ingested or only present on the surface. Adequate surface decontamination methods must be established to elucidate if salmonella is ingested or not. However, as the entire mealworm is normally used, this may from a food safety perspective be less important.
Original languageEnglish
Publication date2019
Number of pages1
Publication statusPublished - 2019
Event70th Annual Meeting of the European Federation of Animal Science (EAAP 2019) - International Convention Centre (ICC) , Ghent, Belgium
Duration: 26 Aug 201929 Aug 2019
Conference number: 70
https://www.eaap2019.org/

Conference

Conference70th Annual Meeting of the European Federation of Animal Science (EAAP 2019)
Number70
LocationInternational Convention Centre (ICC)
CountryBelgium
CityGhent
Period26/08/201929/08/2019
Internet address

Cite this

Jensen, A. N., Johnsen, C., & Hansen, S. H. (2019). Salmonella Typhimurium level in mealworm larvae after exposure to contaminated substrate. Abstract from 70th Annual Meeting of the European Federation of Animal Science (EAAP 2019), Ghent, Belgium.
Jensen, Annette Nygaard ; Johnsen, Christine ; Hansen, Sussie H. / Salmonella Typhimurium level in mealworm larvae after exposure to contaminated substrate. Abstract from 70th Annual Meeting of the European Federation of Animal Science (EAAP 2019), Ghent, Belgium.1 p.
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title = "Salmonella Typhimurium level in mealworm larvae after exposure to contaminated substrate",
abstract = "Mealworms (Tenebrio molitor) for feed and food must be reared on feed-grade materials and findings of Salmonella spp. bacteria, which are important foodborne pathogens, have not yet been reported. However, Salmonella spp. belongs to the family of Enterobacteriaceae, which is found in levels up to 7.5 Log CFU/g in mealworms. This indicates that Salmonella spp. may be able to thrive in the mealworms if introduced into the production. This study aimed to assess the level of salmonella to be found in mealworms after exposure to different salmonella contamination levels in the substrate. The initial contamination level was 2, 4 or 6 Log CFU/g of a Salmonella enterica serotype Typhimurium strain resistant to rifampicin (in-house strain). Samples of mealworm and substrate were collected at start and additional four times until termination at day 7. For each sample, ten-fold dilutions series were prepared from 1 g of homogenized sample in 9 ml saline (0.9{\%} NaCl). Each dilution was plated (0.1) on Nutrient Agar (NA) with rifampicin 50 mg/L to suppress competing bacteria, and incubated overnight at 37oC before counting of colonies. Presumptive S. Typhimuriumrif colonies were verified by slide-agglutination. Preliminary results indicated that the S. Typhimurium level found in mealworm and substrate depended on the initial contamination level while there was no clear effect over time (7 days). In future studies it would be of interest to see for how long salmonella will persist in the mealworms and the substrate after introduction. Also, the quantitative method is limited by a detection level of minimum 1 Log CFU/g and a qualitative approach with enrichment of the samples would be necessary to exclude the presence of salmonella in low numbers. Finally, the entire mealworm was homogenized and analyzed, not allowing concluding whether the salmonella had been ingested or only present on the surface. Adequate surface decontamination methods must be established to elucidate if salmonella is ingested or not. However, as the entire mealworm is normally used, this may from a food safety perspective be less important.",
author = "Jensen, {Annette Nygaard} and Christine Johnsen and Hansen, {Sussie H.}",
year = "2019",
language = "English",
note = "70th Annual Meeting of the European Federation of Animal Science (EAAP 2019), EAAP 2019 ; Conference date: 26-08-2019 Through 29-08-2019",
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Jensen, AN, Johnsen, C & Hansen, SH 2019, 'Salmonella Typhimurium level in mealworm larvae after exposure to contaminated substrate' 70th Annual Meeting of the European Federation of Animal Science (EAAP 2019), Ghent, Belgium, 26/08/2019 - 29/08/2019, .

Salmonella Typhimurium level in mealworm larvae after exposure to contaminated substrate. / Jensen, Annette Nygaard; Johnsen, Christine; Hansen, Sussie H.

2019. Abstract from 70th Annual Meeting of the European Federation of Animal Science (EAAP 2019), Ghent, Belgium.

Research output: Contribution to conferenceConference abstract for conferenceResearchpeer-review

TY - ABST

T1 - Salmonella Typhimurium level in mealworm larvae after exposure to contaminated substrate

AU - Jensen, Annette Nygaard

AU - Johnsen, Christine

AU - Hansen, Sussie H.

PY - 2019

Y1 - 2019

N2 - Mealworms (Tenebrio molitor) for feed and food must be reared on feed-grade materials and findings of Salmonella spp. bacteria, which are important foodborne pathogens, have not yet been reported. However, Salmonella spp. belongs to the family of Enterobacteriaceae, which is found in levels up to 7.5 Log CFU/g in mealworms. This indicates that Salmonella spp. may be able to thrive in the mealworms if introduced into the production. This study aimed to assess the level of salmonella to be found in mealworms after exposure to different salmonella contamination levels in the substrate. The initial contamination level was 2, 4 or 6 Log CFU/g of a Salmonella enterica serotype Typhimurium strain resistant to rifampicin (in-house strain). Samples of mealworm and substrate were collected at start and additional four times until termination at day 7. For each sample, ten-fold dilutions series were prepared from 1 g of homogenized sample in 9 ml saline (0.9% NaCl). Each dilution was plated (0.1) on Nutrient Agar (NA) with rifampicin 50 mg/L to suppress competing bacteria, and incubated overnight at 37oC before counting of colonies. Presumptive S. Typhimuriumrif colonies were verified by slide-agglutination. Preliminary results indicated that the S. Typhimurium level found in mealworm and substrate depended on the initial contamination level while there was no clear effect over time (7 days). In future studies it would be of interest to see for how long salmonella will persist in the mealworms and the substrate after introduction. Also, the quantitative method is limited by a detection level of minimum 1 Log CFU/g and a qualitative approach with enrichment of the samples would be necessary to exclude the presence of salmonella in low numbers. Finally, the entire mealworm was homogenized and analyzed, not allowing concluding whether the salmonella had been ingested or only present on the surface. Adequate surface decontamination methods must be established to elucidate if salmonella is ingested or not. However, as the entire mealworm is normally used, this may from a food safety perspective be less important.

AB - Mealworms (Tenebrio molitor) for feed and food must be reared on feed-grade materials and findings of Salmonella spp. bacteria, which are important foodborne pathogens, have not yet been reported. However, Salmonella spp. belongs to the family of Enterobacteriaceae, which is found in levels up to 7.5 Log CFU/g in mealworms. This indicates that Salmonella spp. may be able to thrive in the mealworms if introduced into the production. This study aimed to assess the level of salmonella to be found in mealworms after exposure to different salmonella contamination levels in the substrate. The initial contamination level was 2, 4 or 6 Log CFU/g of a Salmonella enterica serotype Typhimurium strain resistant to rifampicin (in-house strain). Samples of mealworm and substrate were collected at start and additional four times until termination at day 7. For each sample, ten-fold dilutions series were prepared from 1 g of homogenized sample in 9 ml saline (0.9% NaCl). Each dilution was plated (0.1) on Nutrient Agar (NA) with rifampicin 50 mg/L to suppress competing bacteria, and incubated overnight at 37oC before counting of colonies. Presumptive S. Typhimuriumrif colonies were verified by slide-agglutination. Preliminary results indicated that the S. Typhimurium level found in mealworm and substrate depended on the initial contamination level while there was no clear effect over time (7 days). In future studies it would be of interest to see for how long salmonella will persist in the mealworms and the substrate after introduction. Also, the quantitative method is limited by a detection level of minimum 1 Log CFU/g and a qualitative approach with enrichment of the samples would be necessary to exclude the presence of salmonella in low numbers. Finally, the entire mealworm was homogenized and analyzed, not allowing concluding whether the salmonella had been ingested or only present on the surface. Adequate surface decontamination methods must be established to elucidate if salmonella is ingested or not. However, as the entire mealworm is normally used, this may from a food safety perspective be less important.

M3 - Conference abstract for conference

ER -

Jensen AN, Johnsen C, Hansen SH. Salmonella Typhimurium level in mealworm larvae after exposure to contaminated substrate. 2019. Abstract from 70th Annual Meeting of the European Federation of Animal Science (EAAP 2019), Ghent, Belgium.