Listeria monocytogenes attachment to and detachment from stainless steel surfaces in a simulated dairy processing environment.
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 (10(7) CFU/ml or CFU/g) and incubated at two temperatures (5 and 20 degrees 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 degrees 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 degrees 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 degrees C). The opposite was observed when custard incubated at 20 degrees 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 degrees C) in inoculated yogurt, marked detachment and growth were observed when these coupons were subsequently transferred and incubated at 5 degrees 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.
Poimenidou
Sofia
S
Laboratory of Food Quality Control and Hygiene, Department of Food Science and Technology, Agricultural University of Athens, Athens 11855, Greece.
Belessi
Charalambia A
CA
Giaouris
Efstathios D
ED
Gounadaki
Antonia S
AS
Nychas
George-John E
GJ
Skandamis
Panagiotis N
PN
D000818:Animals; D001422:Bacterial Adhesion; D003080:Cold Temperature; D015169:Colony Count, Microbial; D003611:Dairy Products / Q000382:microbiology; D003612:Dairying / Q000295:instrumentation* / Q000379:methods; D004866:Equipment Contamination; D005511:Food Handling / Q000295:instrumentation* / Q000379:methods; D005516:Food Microbiology; D008089:Listeria monocytogenes / Q000254:growth & development*; D008892:Milk / Q000382:microbiology; D013193:Stainless Steel; D013997:Time Factors; D015014:Yogurt / Q000382:microbiology
D013193:Stainless Steel