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Applied and Environmental Microbiology, November 2005, p. 6730-6735, Vol. 71, No. 11
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.11.6730-6735.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Detection of Salmonella enterica in Naturally Contaminated Liquid Eggs by Loop-Mediated Isothermal Amplification, and Characterization of Salmonella Isolates

Kayoko Ohtsuka,1 Keiko Yanagawa,1 Kosuke Takatori,2 and Yukiko Hara-Kudo2*

Saitama Institute of Public Health, Saitama 338-0824,1 Division of Microbiology, National Institute of Health Sciences, Setagaya-ku, Tokyo 158-8501, Japan2

Received 31 January 2005/ Accepted 28 June 2005

Loop-mediated isothermal amplification (LAMP) assay was effective in detecting Salmonella enterica in naturally contaminated liquid egg samples. Salmonella was detected in 110 samples taken from four egg-breaking plants. The egg samples were pre-enriched in buffered peptone water (BPW) at 37°C for 20 h. The selective enrichment was done in Rappaport-Vassiliadis or tetrathionate broth and plated onto xylose lysine deoxycholate agar and brilliant green agar, modified. In addition, the PCR assay was used to detect Salmonella after pre-enrichment in BPW at 37°C for 20 h. The culture method and PCR assay were compared to the LAMP assay, which was also performed after pre-enrichment in BPW. PCR failed to detect Salmonella in 10% of 110 samples, whereas the culture method and LAMP assay successfully identified Salmonella in all samples. However, the LAMP assay was found to be much more rapid than the culture method and as sensitive in detecting Salmonella from liquid eggs. In all of the egg-breaking plants studied, Salmonella was isolated on most tested days. The positive samples showed that more than 75% of the Salmonella strains had identical genetic patterns when analyzed by pulsed-field gel electrophoresis. This suggests that the same Salmonella strains having survived long periods of time in the plants were contaminating the production line. The LAMP assay is rapid, specific, and sensitive for Salmonella detection in liquid eggs and is able to monitor Salmonella contamination in egg-handling plants more reliably.


* Corresponding author. Mailing address: Division of Microbiology, National Institute of Health Sciences, 1-18-1 Kamiyoga, Setagaya-ku, Tokyo 158-8501, Japan. Phone: 81-3-3700-1141. Fax: 81-3-3700-9527. E-mail: ykudo{at}nihs.go.jp.


Applied and Environmental Microbiology, November 2005, p. 6730-6735, Vol. 71, No. 11
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.11.6730-6735.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.




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