The differential adherence capabilities of two Listeria monocytogenes strains in monoculture and multispecies biofilms as a function of temperature

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.

Section: Discussionsupporting

confidence: 71%

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

Poimenidou¹,

Belessi²,

Giaouris

et al. 2009

“…Previous research demonstrated that cell attachment and biofilm formation by L. monocytogenes are influenced by several factors, including characteristics of strains, physical and chemical properties of the substrate for attachment, growth phase of the bacteria, temperature, growth media, and the presence of other microorganisms (1,5,7,13,17,21,22,30). The properties of L. monocytogenes that make a strain persistent or nonpersistent in a food processing environment are not well understood.…”

mentioning

confidence: 99%

Resistance of Listeria monocytogenes Biofilms to Sanitizing Agents in a Simulated Food Processing Environment

Pan

Breidt

Kathariou

2006

366

199

The objective of this study was to evaluate the resistance of biofilms of Listeria monocytogenes to sanitizing agents under laboratory conditions simulating a food processing environment. Biofilms were initially formed on stainless steel and Teflon coupons using a five-strain mixture of L. monocytogenes. The coupons were then subjected to repeated 24-h daily cycles. Each cycle consisted of three sequential steps: (i) a brief (60 s) exposure of the coupons to a sanitizing agent (a mixture of peroxides) or saline as a control treatment, (ii) storage of the coupons in sterile plastic tubes without any nutrients or water for 15 h, (iii) and incubation of the coupons in diluted growth medium for 8 h. This regimen was repeated daily for up to 3 weeks and was designed to represent stresses encountered by bacteria in a food processing environment. The bacteria on the coupons were reduced in number during the first week of the simulated food processing (SFP) regimen, but then adapted to the stressful conditions and increased in number. Biofilms repeatedly exposed the peroxide sanitizer in the SFP regimen developed resistance to the peroxide sanitizer as well as other sanitizers (quaternary ammonium compounds and chlorine). Interestingly, cells that were removed from the biofilms on peroxide-treated and control coupons were not significantly different in their resistance to sanitizing agents. These data suggest that the resistance of the treated biofilms to sanitizing agents may be due to attributes of extracellular polymeric substances and is not an intrinsic attribute of the cells in the biofilm.

“…These microenvironments include variations in pH, nutrient concentrations, and oxygen levels (17,24). On a surface such as metal, biofilms allow for a variety of microorganisms with differing redox potential requirements to reside in close proximity.…”

mentioning

confidence: 99%

“…Temperature may have had an effect on the production of EPS, which is known to enhance the adherence capability of bacterial cells. SEM studies have shown that Listeria monocytogenes cells produced an EPS matrix at 21°C but not at 10 or 35°C (17). EPS is critical not only for initial adhesion but in the firm anchorage of bacteria to solid surfaces (17) and in the ability of biofilm microorganisms to deal with environmental stresses, such as nutrient limitations, solar radiation, and variations in temperature (20).…”

mentioning

confidence: 99%

Boundaries for Biofilm Formation: Humidity and Temperature

Else

Pantle

Amy

2003

Environmental conditions which define boundaries for biofilm production could provide useful ecological information for biofilm models. A practical use of defined conditions could be applied to the high-level nuclear waste repository at Yucca Mountain. Data for temperature and humidity conditions indicate that decreases in relative humidity or increased temperature severely affect biofilm formation on three candidate canister metals.Biofilms create microenvironments for a consortium of bacteria residing on a substrate. These microenvironments include variations in pH, nutrient concentrations, and oxygen levels (17, 24). On a surface such as metal, biofilms allow for a variety of microorganisms with differing redox potential requirements to reside in close proximity. Microorganisms that carry out microbially influenced corrosion (MIC) can occur in and are facilitated by biofilms (7,8,9). MIC also includes production of microbial metabolites at one location which diffuse to a corrosion site, possibly at another location (15). MIC of metal surfaces results in pitting, crevice corrosion, under-deposit corrosion, and selective leaching. The ability of endolithic and contaminating microbes to form biofilms can ultimately affect performance of structures such as those in the Yucca Mountain repository.Metal biocorrosion occurs in the presence of biofilms; therefore, this study was designed to determine boundary conditions for biofilm formation. Our study had two objectives that address the potential for biofilm production: (i) to determine relative humidity (RH) limits for biofilm formation, and (ii) to determine the boundary limits of biofilm formation on the basis of temperature.Yucca Mountain is located at the Nevada Test Site, 100 miles northwest of Las Vegas, Nevada. Mined Yucca Mountain tuff was collected near the north portal entrance. The surface layer of the tunnel wall was removed by using flamesterilized tools, and the newly exposed rock was collected into sterile, plastic bags and was placed on ice. The rock was transported to the laboratory within 6 h and was stored at Ϫ20°C (14). It was later aseptically crushed into fine grains by using flame-sterilized mortars and pestles.One-centimeter-square coupons were constructed from the following metals: C22 nickel alloy, N-316 stainless steel, and titanium (Metal Samples, Mumford, Ala.). Aseptically crushed rock was transferred to sterile glass petri plates, metal coupons were placed within the crushed rock, and microcosms were placed in chambers held to specific RH and temperature values.To achieve different RH levels, specific saturated salt solutions were placed in the bottom reservoirs of the microcosm chambers (Nalgene Autoclavable Desiccators, Rochester, N.Y.). The salt solutions included KCl (83.6% RH), KI (67.9% RH), and MgCl 2 (32.4% RH). Distilled water was used to create 100% RH. Petri plate microcosms were placed above the salt solution reservoir. Chambers were sealed with highvacuum grease (Dow Corning, Midland, Mich.), and RH levels were checked by ...