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Applied and Environmental Microbiology, November 2009, p. 7182-7188, Vol. 75, No. 22
0099-2240/09/$08.00+0     doi:10.1128/AEM.01359-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Listeria monocytogenes Attachment to and Detachment from Stainless Steel Surfaces in a Simulated Dairy Processing Environment{triangledown}

Sofia Poimenidou,1 Charalambia A. Belessi,1 Efstathios D. Giaouris,2 Antonia S. Gounadaki,1 George-John E. Nychas,2 and Panagiotis N. Skandamis1*

Laboratory of Food Quality Control and Hygiene,1 Laboratory of Microbiology and Biotechnology of Foods, Department of Food Science and Technology, Agricultural University of Athens, Athens, Greece2

Received 10 June 2009/ Accepted 9 September 2009

The presence of pathogens in dairy products is often associated with contamination via bacteria attached to food-processing equipment, especially from areas where cleaning/sanitation is difficult. In this study, the attachment of Listeria monocytogenes on stainless steel (SS), followed by detachment and growth in foods, was evaluated under conditions simulating a dairy processing environment. Initially, SS coupons were immersed in milk, vanilla custard, and yogurt inoculated with the pathogen (107 CFU/ml or CFU/g) and incubated at two temperatures (5 and 20°C) for 7 days. By the end of incubation, cells were mechanically detached from coupons and used to inoculate freshly pasteurized milk which was subsequently stored at 5°C for 20 days. The suspended cells in all three products in which SS coupons were immersed were also used to inoculate freshly pasteurized milk (5°C for 20 days). When SS coupons were immersed in milk, shorter lag phases were obtained for detached than for planktonically grown cells, regardless of the preincubation temperature (5 or 20°C). The opposite was observed when custard incubated at 20°C was used to prepare the two types of inocula. However, in this case, a significant increase in growth rate was also evident when the inoculum was derived from detached cells. In another parallel study, while L. monocytogenes was not detectable on SS coupons after 7 days of incubation (at 5°C) in inoculated yogurt, marked detachment and growth were observed when these coupons were subsequently transferred and incubated at 5°C in fresh milk or/and custard. Overall, the results obtained extend our knowledge on the risk related to contamination of dairy products with detached L. monocytogenes cells.

* Corresponding author. Mailing address: Laboratory of Food Quality Control and Hygiene, Department of Food Science and Technology, Agricultural University of Athens, Iera Odos 75, Athens 11855, Greece. Phone: 30 210 529 4684. Fax: 30 210 529 4683. E-mail: pskan{at}aua.gr

{triangledown} Published ahead of print on 18 September 2009.

Applied and Environmental Microbiology, November 2009, p. 7182-7188, Vol. 75, No. 22
0099-2240/09/$08.00+0     doi:10.1128/AEM.01359-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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