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Applied and Environmental Microbiology, November 2007, p. 7388-7391, Vol. 73, No. 22
0099-2240/07/$08.00+0     doi:10.1128/AEM.00552-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Development of a Method for Detection of Giardia duodenalis Cysts on Lettuce and for Simultaneous Analysis of Salad Products for the Presence of Giardia Cysts and Cryptosporidium Oocysts{triangledown}

N. Cook,1 R. A. B. Nichols,2 N. Wilkinson,1 C. A. Paton,2 K. Barker,1 and H. V. Smith2*

Central Science Laboratory, Sand Hutton, York YO41 1LZ, United Kingdom,1 Scottish Parasite Diagnostic Laboratory, Stobhill Hospital, Balornock Road, Glasgow G21 3UW, United Kingdom2

Received 9 March 2007/ Accepted 10 September 2007

We report a method for detecting Giardia duodenalis cysts on lettuce, which we subsequently use to examine salad products for the presence of Giardia cysts and Cryptosporidium oocysts. The method is based on four basic steps: extraction of cysts from the foodstuffs, concentration of the extract and separation of the cysts from food materials, staining of the cysts to allow their visualization, and identification of cysts by microscopy. The concentration and separation steps are performed by centrifugation, followed by immunomagnetic separation using proprietary kits. Cyst staining is also performed using proprietary reagents. The method recovered 46.0% ± 19.0% (n = 30) of artificially contaminating cysts in 30 g of lettuce. We tested the method on a variety of commercially available natural foods, which we also seeded with a commercially available internal control, immediately prior to concentration of the extract. Recoveries of the Texas Red-stained Giardia cyst and Cryptosporidium oocyst internal controls were 36.5% ± 14.3% and 36.2% ± 19.7% (n = 20), respectively. One natural food sample of organic watercress, spinach, and rocket salad contained one Giardia cyst 50 g–1 of sample as an indigenous surface contaminant.

* Corresponding author. Mailing address: Scottish Parasite Diagnostic Laboratory, Stobhill Hospital, 133 Balornock Road, Glasgow G21 3UW, United Kingdom. Phone: 44 141 201 3028. Fax: 44 141 201 3029. E-mail: huw.smith{at}northglasgow.scot.nhs.uk

{triangledown} Published ahead of print on 21 September 2007.

Applied and Environmental Microbiology, November 2007, p. 7388-7391, Vol. 73, No. 22
0099-2240/07/$08.00+0     doi:10.1128/AEM.00552-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.





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