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T1-04 Rapid Quantitative Detection and Genotyping of Staphylococcus aureus in Retailed Frozen Flour and Rice Products

Monday, August 1, 2016: 9:15 AM
240 (America's Center - St. Louis)
Chunlei Shi, Shanghai Jiao Tong University, Shanghai, China
Yi Zhang, Shanghai Jiao Tong University, Shanghai, China
Minghui Song, Shanghai Jiao Tong University, Shanghai, China
Wenyao Chen, Shanghai Jiao Tong University, Shanghai, China
Yalong Bai, Shanghai Jiao Tong University, Shanghai, China
Yan Cui, Shanghai Jiao Tong University, Shanghai, China
Xianming Shi, Shanghai Jiao Tong University, Shanghai, China
Audio File Recorded Presentation
Introduction: Frozen flour and rice products are easily contaminated by Staphylococcus aureus. The contamination of S. aureus in frozen flour and rice products is allowed in a limited amount below 104 CFU/g, however, the corresponding quantitative method for S. aureus is plating-count based, which is time-and labor-consuming. There is a data gap on the contamination of S. aureusto frozen flour and rice products.

Purpose: It is aimed to establish a nanomagnetic-PCR based quantitative method for S. aureus without pre-enrichment and investigate the contamination level of S. aureus in retailed frozen flour and rice products.

Methods: A new rapid quantitative detection method for the S.aureus contamination in food samples was built up by combining nano-magnetic separation with TaqMan Real-time PCR. Frozen flour and rice products samples were collected to isolate and identify the presence of S. aureus. The S. aureus isolates were screened for their enterotoxin gene diversity by PCR amplification of 18 enterotoxin genes(sea-see, seg-ser and seu), and Multilocus Sequence Typing (MLST) and eBURST analysis.

Results: In total, 288 frozen samples were collected and the total positive rate of S. aureus was 30.56%(88/288). After confirmation, 124 isolates were acquired. The new rapid nanomagnetic-PCR based quantitative method was compared with the reference plating method in 32 S. aureus positive samples, and there was no remarkable difference(P>0.05) between the two methods. The meat-stuffing samples had the highest contamination rate of 41.44% and the highest contamination level which ranged from 2.00×103 to 1.21×105 CFU/g.

Among the 124 isolates, 89.52%(111/124) were positive for enterotoxin genes. Among these positive isolates, 5 maximally contained 10 enterotoxin genes. The sep gene was the most detected(44.35%, 55/124), followed by sei(43.55%, 54/124) and seg(42.74%, 53/124). The isolates were scattered in 36 STs including 5 new ST types and attributed to 19 CCs. ST-7 and CC7 represented the largest ST (27/124) and clonal complex(37/124). And ST-7 had the most diversified enterotoxin genes. The five traditional enterotoxin genes(sea-see) were almost distributed in 4 CCs (CC1, CC5, CC25 and CC7).

Significance: It can be used for food safety monitoring and risk assessment.

Back to: Technical Session 1 – Laboratory and Detection Methods
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