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

Abstract

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°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.

Swab sample preparation and viable real-time PCR methodologies for the recovery of Escherichia coli, Staphylococcus aureus or Listeria monocytogenes from artificially contaminated food processing surfaces

“…The coupons were prepared as per Poimenidou et al (2009). A set of coupons were generated simulating food processing environments which varied in contamination using swab suspension A: high (h; undiluted suspension A), moderate (m; 1/10 dilution of suspension A in 0.85% saline water) and low (l; 1/100 dilution of suspension A in 0.85% saline water).…”

Attachment and Biofilm Formation by Salmonella in Food Processing Environments

“…Adhesion of Salmonella to food surfaces was the first published report on foodborne bacterial biofilm (Duguid et al, 1966). Since that time, many documents have described the ability of foodborne pathogens to attach to various surfaces and form biofilms, including L. monocytogenes (Blackman & Frank, 1996;Chorianopoulos et al, 2011;di Bonaventura et al, 2008;Poimenidou et al, 2009), Salmonella enterica (Chia et al, 2009;Giaouris et al, 2005;Giaouris & Nychas, 2006;Habimana et al, 2010b;Joseph et al, 2001;Kim & Wei, 2007, 2009Oliveira et al, 2006;Marin et al, 2009;Rodrigues et al, 2011;Solomon et al, 2005;Stepanović et al, 2003Stepanović et al, , 2004, Yersinia enterocolitica (Kim et al, 2008), Campylobacter jejuni (Joshua et al, 2006) and Escherichia coli O157:H7 (Habimana et al, 2010a;Skandamis et al, 2009). Modern food processing supports and selects for biofilm forming bacteria on food-contact surfaces due to mass production of products, lengthy production cycles and vast surface areas for biofilm development (Lindsay & von Holy, 2006).…”

Quorum Sensing in the Context of Food Microbiology

“…However, taking into account that Salmonella possess SdiA, a receptor for AHLs which may be produced by resident flora on food contact surfaces (80,115), the effect of AHLs on biofilm formation by this pathogen in multispecies environments needs further study. The challenge becomes more intriguing given that microflora on inadequately cleaned and disinfected food industry surfaces is a complex community, unlike the pure-species biofilms studied in the laboratory (10,96,112). The interactions between the different species may influence the biofilm-forming capacity of individual strains, and this may be a QS-mediated process (48).…”

“…The suggestion that these QS compounds can also act as probes or proxies, thereby offering an alternative angle to communicating cell density, by providing individual cells with information on the diffusion and flow properties of their environment, preventing the wasteful synthesis of "expensive" extracellular substances, such as exoenzymes, bacteriocins, siderophores, and other effectors (41,53,96), could possibly assist in explaining these findings (24). Provided that these substances remain in the (immediate) environment surrounding cells, they may increase nutrient availability and ultimately benefit their producers (104).…”