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P3-10 Comparison of Detection Methods for Salmonella in Egg: Individual Sampling vs. Pooling Sampling

Wednesday, July 25, 2012
Exhibit Hall (Rhode Island Convention Center)
Jun-Ho Park, Konkuk University, Gwangjin-gu, South Korea
Ji-Yeon Hyeon, Konkuk University, Seoul, South Korea
Jung-Whan Chon, Konkuk University, Seoul, South Korea
Hong-Seok Kim, Konkuk University, Seoul, South Korea
Dong-Hyeon Kim, Konkuk University, Gwangjin-gu, South Korea
Kwang-Young Song, Konkuk University, Seoul, South Korea
Jin San Moon, Quarantine and Inspection Agency, Anyang, South Korea
Young Jo Kim, Quarantine and Inspection Agency , Anyang, South Korea
Kun-Ho Seo, Konkuk University, Gwangjin-gu, South Korea
Introduction: Salmonellosis is an important foodborne disease worldwide. The causative agent, Salmonella, is transmitted by many food vehicles, especially eggs. Because Salmonella cells are typically present in low concentrations and only sporadically in individual eggs, sensitive isolation methods and analysis of large numbers of eggs are necessary.

Purpose:  To compare sampling and pre-enrichment methods for detection of Salmonella in eggs.

Methods: A total of 400 different bulk pools were each prepared from the contents of 20 whole shell eggs. Eggs were cracked aseptically and the egg contents were agitated in a stomacher bag and thoroughly mixed manually. Each bulk pool was artificially inoculated with 1 ml of Salmonella in PBS at 88, 68, 53, and 20 CFU per egg pool. Pre-incubation conditions were:  (1) no pre-incubation (2) pre-incubation at room temperature for 4 days (3) pre-incubation at 37 °C for 1 day (4) pre-incubation at 41 °C for 1day. All samples were 25 ml. The isolation method of Salmonella from egg contents was according to the FDA’s Bacteriological Analytical Manual (BAM). Presumptive Salmonella isolates were identified by a Salmonella Enteritidis-specific PCR using the sef14 gene target.

Results: Detection rate of Group (1) was 7/20 (35%) in 88 CFU/pool, 3/20 (15%) in 68 CFU/pool, 0/20 (0%) and 0/20 (0%) in 20 CFU/pool; Group (2) was 18/20 (90%) in 88 CFU/pool, 18/20 (90%) in 68 CFU/pool, 20/20 (100%) in 53 CFU/pool and 5/20 20  CFU/pool; Group (3) was 20/20 (100%) in 88 CFU/pool, 20/20 (100%) in 68 CFU/pool, 9/20 (45%) in 53 CFU/pool, 7/20 (35%) in 20 CFU/pool; and Group (4) was 18/20 (90%) in 88 CFU/pool, 20/20 (100%) in 68 CFU/pool, 18/20 (90%) in 53 CFU/pool, 9/20 (45%) in 20 CFU/pool.

Significance: Use of a 20-egg pool in pre-enrichment was very sensitive compared to the 25 ml direct testing method. In the FDA BAM methods, groups B, C, and D had similar results in different pre-incubation conditions. A method involving a 1-day pre-incubation at 41 °C will save time for detection.

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