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Title: Running title: Yeasts from refrigerated commercial shell eggs Identification of yeasts isolated from commercial shell eggs stored at refrigerated temperatures

Author
item Musgrove, Michael
item Jones, Deana
item Hinton Jr, Arthur
item Ingram, Kimberly
item Northcutt, Julie

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/19/2008
Publication Date: 1/19/2008
Citation: Musgrove, M.T., Jones, D.R., Hinton Jr, A., Ingram, K.D., Northcutt, J.K. 2008. Running title: Yeasts from refrigerated commercial shell eggs. Journal of Food Protection:71:1258-1261

Interpretive Summary: Yeasts and molds can grow on or in eggs, causing spoilage. Little information is available on genera or species of yeasts that contaminate eggs or on which identification methods are best used for isolates collected from eggs. Washed and unwashed eggs (treatments) were collected aseptically on three separate days (replications) from a commercial processing facility and stored for 10 weeks at 4ºC. Yeasts and molds were enumerated from external shell rinses by plating onto acidified potato dextrose agar. Yeast colonies were picked randomly and stored for subsequent identification by gas chromatographic analysis of fatty acid methyl esters using the MIDI Microbial Identification System. Of 688 isolates analyzed, 380 were identified to genus or species. Genera identified by this method included Candida, Cryptococcus, Hansensula, Hyphopichia, Metschnikowia, Rhodotorula, Sporobolomyces, and Torulaspora. Candida spp. accounted for 84.5% of the isolate identifications (321/380). Candida famata was the most prevalent species (n = 120), followed by Candida lusitanae (n = 38). Subsequently, a group of 20 isolates was subjected to molecular or biochemical analyses for comparison with the MIDI results. Biochemical tests were performed using automatic and mini-systems. Biochemical tests and sequencing of rDNA were in agreement for 11 of the isolates, while only 7 of the 20 MIDI identified isolates were in agreement. Candida famata, an anamorph of Debaromyces hansenii var. hansenii was the most commonly identified isolate by all methods. These data indicate that there was a limited correlation between MIDI system and information obtained from molecular databases. However, both systems were able to correctly identify the species most often isolated throughout egg storage. This information will be used by industry and researchers interested in identifying yeasts that contaminate and spoil eggs.

Technical Abstract: Yeasts and molds can grow on or in eggs, causing spoilage. Washed and unwashed eggs (treatments) were collected aseptically on three separate days (replications) from a commercial processing facility and stored for 10 weeks at 4ºC. Ten eggs from each treatment were sampled weekly (110 eggs/treatment/replication). Yeasts and molds were enumerated from external shell rinses by plating onto acidified potato dextrose agar. Yeast colonies were picked randomly and stored for subsequent identification by gas chromatographic analysis of fatty acid methyl esters using the MIDI Microbial Identification System. Of 688 isolates analyzed, 380 were identified to genus or species. Genera identified by this method included Candida, Cryptococcus, Hansensula, Hyphopichia, Metschnikowia, Rhodotorula, Sporobolomyces, and Torulaspora. Candida spp. accounted for 84.5% of the isolate identifications (321/380). Candida famata was the most prevalent species (n = 120), followed by Candida lusitanae (n = 38). Subsequently, a group of 20 isolates was subjected to molecular or biochemical analyses for comparison with the MIDI results. Biochemical tests were performed using automatic and mini-systems. Biochemical tests and sequencing of rDNA were in agreement for 11 of the isolates, while only 7 of the 20 MIDI identified isolates were in agreement. Candida famata, an anamorph of Debaromyces hansenii var. hansenii was the most commonly identified isolate by all methods. These data indicate that there was a limited correlation between MIDI system and information obtained from molecular databases. However, both systems were able to correctly identify the species most often isolated throughout egg storage.