The adherence of Salmonella Enteritidis PT4 to stainless steel: the importance of the air-liquid interface and nutrient availability

Biofilm formation on stainless steel by Salmonella enterica serovar Enteritidis PT4 during growth in three different nutritious conditions was studied. The ability of micro-organisms to generate biofilms on the stainless steel surfaces was studied for a total period of 18 days at 20 degrees C, under three different experimental treatments: (i) growth medium (tryptone soy broth) was not refreshed (no further nutrients were provided) during the incubation period, (ii) growth medium was renewed every 2 days and (iii) growth medium was renewed every 2 days and at the same time the planktonic cells from the old medium were transferred to the new fresh medium. It was found that biofilms developed better and a higher number of adherent cells (ca. 10(7) cfu/cm(2)) were recovered when the organism was grown in periodically renewed nutrient medium than when the growth medium was not refreshed. Regardless of the availability of nutrients, biofilm development was better (range 2-3 logs greater) when coupons were not totally covered by the growth medium and part of the surface was exposed to the air-liquid interface, than when coupons were submerged in the medium. The results suggest that existence of air-liquid interface and adequate nutrient conditions provide the best environment for Salmonella Enteritidis PT4 biofilm formation on stainless steel. The possible role of stationary phase planktonic cells in biofilm development by sessile/attached microbial cells is also discussed.     

Salmonella enterica Enteritidis biofilm formation and viability on regular and triclosan-impregnated bench cover materials

Contamination of food contact surfaces by microbes such as Salmonella is directly associated with substantial industry costs and severe foodborne disease outbreaks. Several approaches have been developed to control microbial attachment; one approach is the development of food contact materials incorporating antimicrobial compounds. In the present study, Salmonella enterica Enteritidis adhesion and biofilm formation on regular and triclosan-impregnated kitchen bench stones (silestones) were assessed, as was cellular viability within biofilms. Enumeration of adhered cells on granite, marble, stainless steel, and silestones revealed that all materials were prone to bacterial colonization (4 to 5 log CFU/cm(2)), and no significant effect of triclosan was found. Conversely, results concerning biofilm formation highlighted a possible bacteriostatic activity of triclosan; smaller amounts of Salmonella Enteritidis biofilms were formed on impregnated silestones, and significantly lower numbers of viable cells (1 × 10(5) to 1 × 10(6) CFU/cm(2)) were found in these biofilms than in those on the other materials (1 × 10(7) CFU/cm(2)). All surfaces tested failed to promote food safety, and careful utilization with appropriate sanitation of these surfaces is critical in food processing environments. Nevertheless, because of its bacteriostatic activity, triclosan incorporated into silestones confers some advantage for controlling microbial contamination.     

Thermal injury and recovery of Salmonella enterica serovar enteritidis in ground chicken with temperature, pH, and sodium chloride as controlling factors

Cells of Salmonella enterica serovar Enteritidis were grown at 25 and 35 degrees C, heat injured (55, 60, and 62.5 degrees C), and recovered in tryptic soy broth (TSB) at various NaCl concentrations (2.0 and 3.5%) and pH levels (5.5 and 6.5). To assess the interactions of growth temperature, heating temperature, NaCl concentration and pH on the thermal injury and recovery of Salmonella Enteritidis in ground chicken, a randomized design with each experimental combination was used. When a logistic equation for nonlinear survival curves was used, D-values of cells of Salmonella Enteritidis grown at 25 degrees C were 7.60, 5.73, and 4.81 min at 55, 60, and 62.5 degrees C, respectively. For cells grown at 35 degrees C, the D-values were 12.38, 7.45, and 5.70 min at 55, 60, and 62.5 degrees C. The influence of tryptic soy agar and double modified lysine agar (DMLIA) on the recovery of heat-injured cells was determined. Recovery was significantly reduced on DMLIA at increased pH levels and NaCl concentrations. Higher numbers of cells were recovered in TSB with 2.0% NaCl than in TSB with 3.5% NaCl. It was observed that the rate of recovery of heat-injured cells was similar at each pH. Therefore, a pH range of 5.5 to 6.5 does not have a major inhibitory effect on the recovery of Salmonella Enteritidis.     

Biofilm formation of Salmonella Typhimurium on stainless steel and acrylic surfaces as affected by temperature and pH level

The effect of temperature (28, 37 and 42 °C) and pH (6 and 7) on the biofilm formation capability of Salmonella Typhimurium on stainless steel and acrylic was investigated. The rate of biofilm formation increased with increasing temperature and pH, while the number of attached cells after 240 h decreased with increasing temperature and was not different between pH 6 and 7. The surface hydrophobicity of bacterial cells was not significantly (p > 0.05) different among tested conditions. Electron-donating/accepting properties changed with pH and temperature, although these changes did not correlate with the ability to form biofilms under respective conditions. Attachment of S. Typhimurium showed a preference for stainless steel compared to acrylic surfaces under all conditions tested. The results suggest that salmonellae were less adherent to acrylic than to stainless steel surfaces; thus, acrylic-type surfaces should be considered for use in the food industry over stainless steel where applicable. The rate of biofilm formation increased at higher temperatures and pH levels within the tested ranges. Hurdle technology using lower temperatures reduced pH may help delay biofilm formation on food contact surfaces contaminated with S. Typhimurium.     

Biofilm formation by salmonella spp. on food contact surfaces and their sensitivity to sanitizers

Biofilm formation by two poultry isolates of Salmonella on three commonly used food contact surfaces viz plastic, cement and stainless steel were studied. Biofilm formation of both the isolates showed a similar trend with the highest density being on plastic followed by cement and steel. Salmonella weltevreden formed biofilm with a cell density of 3.4 x 10(7), 1.57 x 10(6) and 3 x 10(5) cfu/cm2 on plastic, cement and steel respectively while Salmonella FCM 40 biofilm on plastic, cement and steel were of the order of 1.2 x 10(7), 4.96 x 10(6) and 2.23 x 10(5) cfu/cm2 respectively. The sensitivity of the biofilm cells grown on these surfaces to different levels of two sanitizers namely hypochlorite and iodophor for varying exposure times was studied. Biofilm cells offered greater resistance when compared to their planktonic counterparts. Such biofilm cells in a food processing unit are not usually removed by the normal cleaning procedure and therefore could be a source of contamination of foods coming in contact with such surfaces.     

Effects of nutritional and environmental conditions on Salmonella sp. biofilm formation

Biofilm formation on food industry surfaces has important health and economic consequences, since they can serve as a potential source of contamination for food products, which may lead to food spoilage or transmission of diseases. Salmonella sp. is one of the most important foodborne pathogens and several studies have led to the discovery that these bacteria are capable of adhering and forming biofilms on different surfaces. The attachment of bacterial cells is affected by several factors, including the medium in which they are grown, motility, growth phase of the cells, type and properties of the inert material, presence of organic material, temperature, pH, contact time, and so on. This investigation focused on the study and quantification of the effects of temperature (20 to 40 °C), pH (4.5 to 7.5), and medium composition (0.5 to 2.5 g/L of peptone) on biofilm formation by Salmonella sp. on stainless steel through surface response modeling. Results highlighted that the target strain was able to adhere on stainless steel, under all the conditions tested. To assess potential differences, the aptitude to biofilm formation (ABF), defined as the time necessary to start adhesion on the surface, was calculated by using the Gompertz equation. This parameter was modeled through a stepwise regression procedure and experimental conditions resulting in the greater ABF were growth in poor media (1.0 to 1.5 g/L of peptone), incubation temperature of about 30 °C, pH close to 6.0. Practical Application: The importance of this work lies in its extension of our knowledge about the effect of different environmental conditions on Salmonella adherence to stainless steel food-processing equipment, as a better understanding of biofilms may provide valuable pathways for the prevention of biofilm formation.     

创伤弧菌致病性及其毒力因子研究进展

研究26株创伤弧菌（Vibrio vulnificus,Vv）产生物被膜情况及影响生物被膜形成的因素,为有效控制创伤弧菌形成生物被膜提供理论依据。本研究采用刚果红平板法、改良试管法及改良微孔板法分析25株创伤弧菌分离株及1株标准菌株形成生物被膜的能力,从中选出一株产膜能力最强的菌株,并研究不同初始菌浓度、温度及时间、pH、NaCl浓度、金属阳离子以及接触材料对其生物被膜形成的影响。结果显示,所选菌株中具有生物被膜形成能力的有25株（96.15%）。其中菌株VvK产膜能力最强,在25 ℃条件下,初始菌浓度为10⁸ CFU/mL,含3% NaCl、pH8~9培养24 h时,生物被膜形成量最大。而添加一定浓度的金属阳离子（Cu²⁺、Mn²⁺、Ca²⁺、Mg²⁺）后,生物被膜的形成受到不同程度的抑制,其抑制能力依次降低。菌株VvK在接触亲水性表面（不锈钢和玻璃）时生物被膜形成量显著高于疏水性表面（聚苯乙烯）,且在不锈钢表面形成量最大。不同创伤弧菌生物被膜形成能力具有较大的差异,且在不同培养条件下具有特定的规律,需引起重点关注。     

Effect of acid tolerance response (ATR) on attachment of Listeria monocytogenes Scott A to stainless steel under extended exposure to acid or/and salt stress and resistance of sessile cells to subsequent strong acid challenge

The aim of this study was to investigate the potential effect of adaptive stationary phase acid tolerance response (ATR) of Listeria monocytogenes Scott A cells on their attachment to stainless steel (SS) under low pH or/and high salt conditions and on the subsequent resistance of sessile cells to strong acid challenge. Nonadapted or acid-adapted stationary-phase L. monocytogenes cells were used to inoculate (ca. 10? CFU/ml) Brain Heart (BH) broth (pH 7.4, 0.5% w/v NaCl) in test tubes containing vertically placed SS coupons (used as abiotic substrates for bacterial attachment). Incubation was carried out at 16 °C for up to 15 days, without any nutrient refreshment. L. monocytogenes cells, prepared as described above, were also exposed to low pH (4.5; adjusted with HCl) or/and high salt (5.5% w/v NaCl) stresses, during attachment. On the 5th, 10th and 15th day of incubation, cells attached to SS coupons were detached (through bead vortexing) and enumerated (by agar plating). Results revealed that ATR significantly (p<0.05) affected bacterial attachment, when the latter took place under moderate acidic conditions (pH 4.5, 0.5 or 5.5% w/v NaCl), with the acid-adapted cells adhering slightly more than the nonadapted ones. Regardless of acidity/salinity conditions during attachment, ATR also enhanced the resistance of sessile cells to subsequent lethal acid challenge (exposure to pH 2 for 6 min; pH adjusted with either hydrochloric or lactic acid). The trend observed with viable count data agreed well with conductance measurements, used to indirectly quantify remaining attached bacteria (following the strong acid challenge) via their metabolic activity. To sum, this study demonstrates that acid adaptation of L. monocytogenes cells during their planktonic growth enhances their subsequent attachment to SS under extended exposure (at 16 °C for up to 15 days) to mild acidic conditions (pH 4.5), while it also improves the resistance of sessile cells to extreme acid treatment (pH 2). Therefore, the ATR of bacterial cells should be carefully considered when applying acidic decontamination strategies to eradicate L. monocytogenes attached to food processing equipment.     

Autoinducer-2 activity of gram-negative foodborne pathogenic bacteria and its influence on biofilm formation

ABSTRACT:  This study evaluated whether autoinducer-2 (AI-2) activity would be associated with biofilm formation by Salmonella and Escherichia coli O157:H7 strains on food contact surfaces. In study I, a Salmonella Typhimurium DT104 strain and an E . coli O157:H7 strain, both AI-2 positive, were individually inoculated into 50 mL of Luria–Bertani (LB) or LB + 0.5% glucose (LBG) broth, without or with stainless steel or polypropylene ( Salmonella ) coupons. At 0, 14 ( Salmonella ), 24, 48, and 72 h of storage (25 °C), cells in suspension and detached cells from the coupons, obtained by vortexing, were enumerated on tryptic soy agar. In study II, a Salmonella Thompson AI-2-positive strain and an AI-2-negative strain, and an E . coli O157:H7 AI-2-positive strain and an AI-2-negative strain were inoculated into LB broth with stainless steel coupons. Cells were enumerated as in study I. In both studies, AI-2 activity was determined in cell-free supernatants. Cell numbers of S . Typhimurium DT104 on biofilms were higher ( P < 0.05) in LB than those in LBG, while the E . coli O157:H7 strain showed no difference ( P ≥ 0.05) in biofilm cell counts between LB and LBG after storage for 72 h. Both S . Typhimurium DT104 and E . coli O157:H7 strains produced higher ( P < 0.05) AI-2 activity in LBG than LB cell suspensions. Cell counts of AI-2-positive and-negative S . Thompson and E . coli O157:H7 strains were not different ( P ≥ 0.05) within suspensions or coupons (study II). The results indicated that, under the conditions of this study, AI-2 activity of the pathogen strains tested may not have a major influence on biofilm formation on food contact surfaces, which was similar between AI-2-positive and -negative strains.     

Use of titanium dioxide (TiO2) photocatalysts as alternative means for Listeria monocytogenes biofilm disinfection in food processing

The aim of this work was to study the photocatalytic activity of titanium dioxide (TiO₂) against Listeria monocytogenes bacterial biofilm. Different TiO₂ nanostructured thin films were deposited on surfaces such as stainless steel and glass using the doctor-blade technique. All the surfaces were placed in test tubes containing Brain Heart (BH) broth and inoculated with L. monocytogenes. Test tubes were then incubated for 10 days at 16 °C in order to allow biofilm development. After biofilm formation, the surfaces were illuminated by ultraviolet A light (UVA; wavelength of 315-400 nm). The quantification of biofilms was performed using the bead vortexing method, followed by agar plating and/or by conductance measurements (via the metabolic activity of biofilm cells). The presence of the TiO₂ nanoparticles resulted in a fastest log-reduction of bacterial biofilm compared to the control test. The biofilm of L. monocytogenes for the glass nanoparticle 1 (glass surface modified by 16% w/v TiO₂) was found to have decreased by 3 log CFU/cm² after 90 min irradiation by UVA. The use of TiO₂ nanostructured photocatalysts as alternative means of disinfecting contaminated surfaces presents an intriguing case, which by further development may provide potent disinfecting solutions. Surface modification using nanostructured titania and UV irradiation is an innovative combination to enhance food safety and economizing time and money.     

Biofilm Formation of Staphylococcus aureus on Various Surfaces and Their Resistance to Chlorine Sanitizer

This study investigated the effect of material types (polystyrene, polypropylene, glass, and stainless steel) and glucose addition on Staphylococcus aureus biofilm formation, and the relationship between biofilm formation measured by crystal violet (CV) staining and the number of biofilm cells determined by cell counts was studied. We also evaluated the efficacy of chlorine sanitizer on inhibiting various different types of S. aureus biofilms on the surface of stainless steel. Levels of biofilm formation of S. aureus were higher on hydrophilic surfaces (glass and stainless steel) than on hydrophobic surfaces (polypropylene and polystyrene). With the exception of biofilm formed on glass, the addition of glucose in broth significantly increased the biofilm formation of S. aureus on all surfaces and for all tested strains (P ≤ 0.05). The number of biofilm cells was not correlated with the biomass of the biofilms determined using the CV staining method. The efficacy of chlorine sanitizer against biofilm of S. aureus was not significantly different depending on types of biofilm (P > 0.05). Therefore, further studies are needed in order to determine an accurate method quantifying levels of bacterial biofilm and to evaluate the resistance of bacterial biofilm on the material surface.     

Surface material, temperature, and soil effects on the survival of selected foodborne pathogens in the presence of condensate

The effects of surface type (stainless steel, acetal resin, and fiberglass reinforced plastic wall paneling [FRP]), soil, and temperature on the survival of Listeria monocytogenes, Salmonella spp., and Yersinia enterocolitica, in the presence of condensate were evaluated. Surface coupons--half soiled with sterile porcine serum--were exposed to cell suspensions made from individual five-strain cocktails composed of organisms from the same genus (10(7) CFU/ml) in Butterfield's phosphate buffer and incubated for 2 h at 25 degrees C allowing attachment of cells to coupon surfaces. Coupons were rinsed to remove unattached cells, incubated at either 4 or 10 degrees C under condensate-forming conditions, and sampled at six time intervals over a 15-day period. For enumeration, cells were removed from the coupons by vigorous shaking in 100 ml of Butterfield's phosphate buffer with 3 g of glass beads and plated on tryptic soy agar with 0.6% yeast extract. Stainless steel did not support the survival of Listeria as well as acetal resin or FRP. Acetal resin and stainless steel were less supportive of Salmonella than FRP. All surfaces supported the survival of Yersinia over the 15-day trial equally. Temperature had little effect on survival of all organisms across all surfaces with one exception. However, Yersinia displayed growth on FRP at 10 degrees C. but death at 4 degrees C. Serum had a protective effect on L. monocytogenes on all surfaces, with populations sustained at significantly (P < or = 0.05) higher numbers over time than unsoiled coupons. Serum didnot effect survival of Salmonella or Yersinia on stainless steel, acetal resin, or FRP.     

Biofilm formation by multidrug-resistant Salmonella enterica serotype typhimurium phage type DT104 and other pathogens

The biofilm-forming capability of Salmonella enterica serotypes Typhimurium and Heidelberg, Pseudomonas aeruginosa, Listeria monocytogenes, Escherichia coli O157:H7, Klebsiella pneumoniae, and Acinetobacter baumannii isolated from humans, animal farms, and retail meat products was evaluated by using a microplate assay. The tested bacterial species showed interstrain variation in their capabilities to form biofilms. Strong biofilm-forming strains of S. enterica serotypes, E. coli O157: H7, P. aeruginosa, K. pneumoniae, and A. baumannii were resistant to at least four of the tested antibiotics. To understand their potential in forming biofilms in food-processing environments, the strong biofilm formers grown in beef, turkey, and lettuce broths were further investigated on stainless steel and glass surfaces. Among the tested strains, Salmonella Typhimurium phage type DT104 (Salmonella Typhimurium DT104) isolated from retail beef formed the strongest biofilm on stainless steel and glass in beef and turkey broths. K. pneumoniae, L. monocytogenes, and P. aeruginosa were also able to form strong biofilms on the tested surface materials. Salmonella Typhimurium DT104 developed a biofilm on stainless steel in beef and turkey broths through (i) initial attachment to the surface, (ii) formation of microcolonies, and (iii) biofilm maturation. These findings indicated that Salmonella Typhimurium DT104 alongwith other bacterial pathogens could be a source of cross-contamination during handling and processing of food.     

不同环境条件对隆德假单胞菌生物被膜形成能力的影响

为研究环境条件对食品腐败菌隆德假单胞菌（Pseudomonas lundensis,PL）生物被膜形成能力的影响,采用微孔板结晶紫法测定不同的营养条件、接种浓度、pH、NaCl和Mg2+浓度条件下其生物被膜量,用激光共聚焦扫描显微镜观测其在不锈钢材料上的黏附和结构特征。结果表明,PL生物被膜的形成量在营养胁迫下降低,稀释TSB培养基50倍造成的营养胁迫使其生物被膜量从1.75±0.35降低至0.24±0.17。PL接种量从1.3×107 CFU/mL降至2.5×104 CFU/mL时,其生物被膜的形成量无显著差异（P>0.05）,在pH为8.0时PL形成生物被膜量最多,1.25%以上的葡萄糖、4%以上的NaCl和0.5%的Mg2+能够显著（P<0.05）抑制PL生物被膜的形成。激光共聚焦显微镜观测结果表明该菌在一定浓度下具有在不锈钢表面形成典型生物被膜的能力。PL生物被膜形成能力受营养条件、葡萄糖浓度、pH、NaCl浓度、Mg2+等环境因子的影响。     

四种不同接触表面蜡样芽孢杆菌菌膜形成的影响

为了解食源性致病菌蜡样芽孢杆菌在食品加工环境中菌膜形成能力,以玻璃、不锈钢、聚氯乙烯、聚丙烯为接触面,采用超声波平板菌落计数法测定不同环境因素(温度、pH、氯化钠、葡萄糖、苯甲酸钠及山梨酸钾)、不同材料表面蜡样芽孢杆菌(B.cereus)菌膜形成的变化趋势。结果表明:四种材质表面形成B.cereus菌膜能力的大小顺序为:玻璃 > 不锈钢 > 聚氯乙烯 > 聚丙烯。其中,30 ℃,pH7.0时菌膜形成量最大,添加低浓度葡萄糖(4.0%)或氯化钠(0.5%)对B.cereus菌膜形成有显著促进作用(p<0.05),添加0.15%苯甲酸钠、山梨酸钾的菌膜形成量显著高于添加0.10%的菌膜形成量(p<0.05)。本研究为蜡样芽孢杆菌风险评估提供基础数据,为食品工业蜡样芽孢杆菌菌膜的预防和控制奠定基础,为改进蜡样芽孢杆菌的清洗控制措施提供参考。     

Evaluation of dislodging methods for laboratory-grown bacterial biofilms

The efficacy ofPseudomonas fluorescensandBacillus subtilisbiofilm removal from stainless steel and polyurethane test surfaces by vortexing, sonication or shaking with beads, was compared by plate counts and scanning electron microscopy. No significant differences (P0.01) were found between the bacterial counts resulting from the three methods. However, scanning electron microscopy suggested that shaking with beads removed cells as well as residues of extracellular polymeric substances (EPS) more efficiently from both surface types for both bacteria. Therefore, it was concluded that, based on cell counts and microscopy, shaking with beads was the most suitable method to remove attachedP. fluorescensandB. subtilisfrom stainless steel and polyurethane test surfaces.     

Attachment and biofilm formation by various serotypes of Salmonella as influenced by cellulose production and thin aggregative fimbriae biosynthesis

This study was undertaken to quantify thin aggregative fimbriae and cellulose produced by Salmonella and to evaluate their roles in attachment and biofilm formation on polystyrene and glass surfaces. Thin aggregative fimbriae and cellulose produced by four wild-type and two pairs of Salmonella, representing four different colony morphotypes (rdar: red, dry, and rough; pdar: pink, dry, and rough; bdar: brown, dry, and rough; and saw: smooth and white), were quantified. The ability of the Salmonella cells to attach and form biofilms on the selected surfaces was evaluated in Luria-Bertani (LB) broth with or without salt (0.5%) or glucose (2%) at 28 degrees C during a 7-day period. The cells expressing the rdar or pdar colony morphotypes produced significantly greater amounts of thin aggregative fimbriae and cellulose on LB no salt agar, respectively. The cells expressing the rdar colony morphotype attached in higher numbers and formed more biofilm than did the cells expressing the pdar colony morphotype. The members of the pairs expressing the bdar colony morphotype attached more efficiently and formed more biofilm on the tested surfaces than did their counterparts expressing the saw colony morphotype. These results indicated that thin aggregative fimbriae impart attachment ability to Salmonella and, upon coexpression with cellulose, enhance biofilm formation on certain abiotic surfaces. The knowledge acquired in the study may help develop better cleaning strategies for food processing equipment.     

Influence of a nonfavorable environment, egg white, on resistance to heat and disinfectant, adhesion, and virulence of Salmonella enteritidis

Although liquid egg white may be subjected to limited heat treatment when it is used in the fabrication of various foodstuffs, pathogenic bacteria such Salmonella Enteritidis could persist in this environment. Liquid egg white is not a favorable medium for Salmonella growth because of its alkaline pH and iron deficiency and the presence of ovotransferrin. Microorganisms adapted to a nonfavorable environment are often more resistant to stresses than are their laboratory-cultured counterparts. The objective of this study was to determine whether Salmonella exposed to an environment mimicking egg white conditions exhibited modified behavior that could have an impact on food safety. A medium resembling egg white (filtrate of egg white with added ovotransferrin) was used as an adaptation treatment to mimic the stress imparted by the egg white environment. There were no changes in resistance to heat and disinfection, in stainless steel adhesion, or in the virulence of Salmonella Enteritidis cultivated in the egg white medium. Egg white conditions do not appear to make Salmonella more virulent or more difficult to inactivate.     

Fate of Escherichia coli O157:H7 and Salmonella Enteritidis on currency.

The fate of foodborne pathogens Escherichia coli O157:H7 and Salmonella Enteritidis on coin surfaces was determined at room temperature (25 degrees C). A five-strain mixture of E. coli O157:H7 or Salmonella Enteritidis of approximately 5 x 10(4) CFU was applied to the surfaces of sterile U.S. coins (pennies, nickels, dimes, and quarters) and to the surfaces of two control substrata (Teflon and glass coverslips). During storage at room temperature, E. coli O157:H7 survived for 7, 9, and 11 days on the surfaces of pennies, nickels, and dimes and quarters, respectively. However, the pathogen died off within 4 to 7 days on both the Teflon and glass surfaces. Salmonella Enteritidis survived for 1, 2, 4, and 9 days on the surfaces of pennies, nickels, quarters, and dimes, respectively. Unlike E. coli O157:H7, survival of Salmonella Enteritidis was greatest on both Teflon and glass coverslips, with more than 100 cells per substratum detected at the 17th day of storage. Results indicate that coins could serve as potential vehicles for transmitting both E. coli O157:H7 and Salmonella Enteritidis.     

Effect of NaCl on the biofilm formation by foodborne pathogens

This study was designed to evaluate the effect of NaCl on the biofilm formation of Listeria monocytogenes, Staphylococcus aureus, Shigella boydii, and Salmonella Typhimurium. The biofilm cells were cultured in media containing different NaCl concentrations (0% to 10%) for 10 d of incubation at 37 °C using a 24-well polystyrene microtiter plate, collected by swabbing methods, and enumerated using plate count method. The attachment and detachment kinetic patterns were estimated according to the modified Gompertz model. The cell surface hydrophobicity and auto-aggregation were observed at different NaCl concentrations. Most strains showed 2 distinctive phases at lower than 6% NaCl, while the numbers of adhered cells gradually increased throughout the incubation period at 4% to 10% NaCl. At 0% NaCl, the numbers of adhered L. monocytogenes, S. aureus, S. boydii, and S. Typhimurium cells rapidly increased up to 7.04, 6.47, 6.39, and 7.27 log CFU/cm(2), respectively, within 4 d of incubation. The maximum growth rate (k(A)) and specific growth rate (μ(A)) of adherent pathogenic cells were decreased with increasing NaCl concentration. Noticeable decline in the numbers of adherent cells was observed at low concentration levels of NaCl (<2%). The adherence abilities of foodborne pathogens were influenced by the physicochemical surface properties. The hydrophobicity and auto-aggregation enhanced the biofilm formation during the incubation periods. Therefore, this study could provide useful information to better understand the adhesion and detachment capability of foodborne pathogens on food contact surfaces.