The effect of molybdenum on biofilm development

Little is known about the formation and effects of biofilms on stainless steel pipes in freshwater environments, particularly as they are considered as a direct replacement for copper pipes for ‘problem’ water. There is some cause for concern especially as stainless steel cannot claim the inherent biocidal potential of copper. As molybdenum is known to be leached out of stainless steel grade 316, in very small amounts, a study was set up to see if molybdenum could retard the development of biofilms. When a comparison of biofilm viable and total cell counts was made between pure molybdenum metal and stainless steel grade 304, it was found that cell counts were significantly higher (P < 0.05) on grade 304 stainless steel after 5 weeks exposure to flowing water (0.64 m s⁻¹). Molybdenum (above a concentration of 1 g L⁻¹) affected the growth rate of Acinetobacter sp, a pioneering bacterium of biofilms in potable water. Received 18 February 1998/ Accepted in revised form 17 May 1999     

Antimicrobial activity and effectiveness of a combination of sodium hypochlorite and hydrogen peroxide in killing and removing Pseudomonas aeruginosa biofilms from surfaces

AIMS: To evaluate both the antimicrobial activity and the effectiveness of a combination of sodium hypochlorite and hydrogen peroxide (Ox-B) for killing Pseudomonas aeruginosa ATCC 19142 cells and removing P. aeruginosa biofilms on aluminum or stainless steel surfaces. METHODS AND RESULTS: Pseudomonas aeruginosa biofilms were developed in tryptic soy broth containing vertically suspended aluminium or stainless steel plates. Biofilms were exposed to a mixed sodium hypochlorite and hydrogen peroxide solution as a sanitizer for 1, 5 and 20 min. The sanitizer was then neutralized, the cells dislodged from the test surfaces, and viable cells enumerated. Cell morphologies were determined using scanning (SEM) and transmission electron microscopy (TEM). Cell viability was determined by confocal scanning laser microscopy (CSLM). Biofilm removal was monitored by Fourier transform infrared (FTIR) spectrophotometry. Cell numbers were reduced by 5-log to 6-log after 1 min exposure and by 7-log after 5 min exposure to Ox-B. No viable cells were detected after a 20 min exposure. Treatment with equivalent concentrations of sodium hypochlorite reduced viable numbers by 3-log to 4-log after 1 min exposure and by 4-log to 6-log after 5 min, respectively. A 20 min exposure achieved a 7-log reduction. Hydrogen peroxide at test concentration treatments showed no effect. FTIR analysis of treated pseudomonad biofilms on aluminium or stainless steel plates showed either a significant reduction or complete removal of biofilm material after a 5 min exposure to the mixed sodium hypochlorite and hydrogen peroxide solution. SEM and TEM images revealed damage to cell wall and cell membranes. CONCLUSIONS: A combination of sodium hypochlorite and hydrogen peroxide effectively killed P. aeruginosa cells and removed biofilms from both stainless steel and aluminium surfaces. SIGNIFICANCE AND IMPACT OF THE STUDY: The combination of sodium hypochlorite and hydrogen peroxide can be used as an alternative disinfectant and/or biofilm remover of contaminated food processing equipment.     

The effect of turbulent flow and surface roughness on biofilm formation in drinking water

There is considerable interest in both Europe and the USA in the effects of microbiological fouling on stainless steels in potable water. However, little is known about the formation and effects of biofilms, on stainless steel in potable water environments, particularly in turbulent flow regimes. Results are presented on the development of biofilms on stainless steel grades 304 and 316 after exposure to potable water at velocities of 0.32, 0.96 and 1.75 m s⁻¹. Cell counts on slides of stainless steel grades 304 and 316 with both 2B (smooth) and 2D (rough) finishes showed viable and total cell counts were higher at the higher flow rates of 0.96 and 1.75 m s⁻¹, compared to a flow rate of 0.32 m s⁻¹. Extracellular polysaccharide levels were not significantly different (P< 0.05) between each flow rate on all stainless steel surfaces studied. higher levels were found at the higher water velocities. the biofilm attached to stainless steel was comprised of a mixed bacterial flora including Acinetobacter sp, Pseudomonas spp, Methylobacterium sp, and Corynebacterium/Arthrobacter spp. Epifluorescence microscopy provided evidence of rod-shaped bacteria and the formation of stands, possibly of extracellular material attached to stainless steel at high flow rates but not at low flow rates. Received 04 February 1998/ Accepted in revised form 12 February 1999     

Biofilm penetration and disinfection efficacy of alkaline hypochlorite and chlorosulfamates

AIMS: The purpose of this study was to compare the efficacy, in terms of bacterial biofilm penetration and killing, of alkaline hypochlorite (pH 11) and chlorosulfamate (pH 5.5) formulations. METHODS AND RESULTS: Two species biofilms of Pseudomonas aeruginosa and Klebsiella pneumoniae were grown by flowing a dilute medium over inclined stainless steel slides for 6 d. Microelectrode technology was used to measure concentration profiles of active chlorine species within the biofilms in response to treatment at a concentration of 1000 mg total chlorine l(-1). Chlorosulfamate formulations penetrated biofilms faster than did hypochlorite. The mean penetration time into approximately 1 mm-thick biofilms for chlorosulfamate (6 min) was only one-eighth as long as for the same concentration of hypochlorite (48 min). Chloride ion penetrated biofilms rapidly (5 min) with an effective diffusion coefficient in the biofilm that was close to the value for chloride in water. Biofilm bacteria were highly resistant to killing by both antimicrobial agents. Biofilms challenged with 1000 mg l(-1) alkaline hypochlorite or chlorosulfamate for 1 h experienced 0.85 and 1.3 log reductions in viable cell numbers, respectively. Similar treatment reduced viable numbers of planktonic bacteria to non-detectable levels (log reduction greater than 6) within 60 s. Aged planktonic and resuspended laboratory biofilm bacteria were just as susceptible to hypochlorite as fresh planktonic cells. CONCLUSION: Chlorosulfamate transport into biofilm was not retarded whereas hypochlorite transport clearly was retarded. Superior penetration by chlorosulfamate was hypothesized to be due to its lower capacity for reaction with constituents of the biofilm. Poor biofilm killing despite direct measurement of effective physical penetration of the antimicrobial agent into the biofilm demonstrates that bacteria in the biofilm are protected by some mechanism other than simple physical shielding by the biofilm matrix. SIGNIFICANCE AND IMPACT OF THE STUDY: This study lends support to the theory that the penetration of antimicrobial agents into microbial biofilms is controlled by the reactivity of the antimicrobial agent with biofilm components. The finding that chlorine-based biocides can penetrate, but fail to kill, bacteria in biofilms should motivate the search for other mechanisms of protection from killing by antimicrobial agents in biofilms.     

Biofilm reduction by a new burn gel that targets nociception

AIMS: To compare the ability of an amorphous first aid topical gel containing vinegar, citric acid and EDTA (RescuDerm(TM); RESC) and various derivative formulations to eradicate Pseudomonas aeruginosa (PSEUD) and Staphylococcus epidermidis (STAPH) biofilms. METHODS AND RESULTS: 24-h biofilms prepared using the Minimum Biofilm Elimination Concentration (MBEC) Assay System were exposed for 4 or 24 h to the different gel formulations. Citric acid-free, acetic acid-free or acetic acid-free/sodium acetate-supplemented RESC gels reduced PSEUD and STAPH biofilm formation as effectively as RESC. Substituting the weak organic acids with equivalent concentrations of glacial acetic acid reduced the effectiveness of gel against PSEUD and STAPH biofilms by half, but viable bacterial counts still remained below 4 log(10) CFU/peg. Removal of gelling agent and/or EDTA enhanced efficacy against PSEUD but not STAPH biofilms. An acidified placebo gel formulation generated an only marginal bactericidal effect compared to that of RESC. CONCLUSIONS: RESC is a promising new antimicrobial agent. Its weak organic acid content, rather than merely acidic pH, mediates its considerable in vitro bactericidal efficacy against bacterial biofilms. SIGNIFICANCE AND IMPACT OF THE STUDY: These data, taken together with the observation that RescuDerm possesses broad in vitro bactericidal activity against other pathogen species, suggest the potential usefulness of this product for controlling biofilm formation on a variety of cutaneous traumatic and surgical wounds.     

Effects of marine paints on microbial biofilm development on three materials

The development of biofilms of Pseudomonas aeruginosa PAO-1 was studied using modified Robbins devices. Biofilm development was measured using viable counts, acridine orange direct counts (AODC), and a colorimetric method for exopolysaccharide (EPS). Biofilms reached their maximum population 24–72 h after inoculation on coupons with no paint or on coupons coated with marine paint VC-18 without additives. Biofilms on stainless steel contained higher numbers of total cells and of viable cells than biofilms on fiberglass or aluminum. Coating the surfaces with marine paint VC-18 resulted in decreased numbers of cells on stainless steel but had little effect on numbers of cells on fiberglass or aluminum. Addition to the paint of Cu or tributyltin (TBT), the active components in two types of antifouling paints, inhibited the initial development of biofilms. However, by 72–96 h, most biofilms contained the same number of cells as surfaces without additives as shown by both viable counts and AODC. Biofilms that formed on surfaces coated with Cu- or TBT-containing paint did not synthesize more EPS, suggesting that P. aeruginosa PAO-1 does not respond to these compounds by synthesizing more EPS, which could bind the metal and protect the cells. Rather, these biofilms may contain Cu- or TBT-resistant cells. TBT-resistant cells made up 1–10% of the viable counts in biofilms on uncoated stainless steel, but in biofilms on stainless steel coated with marine paint containing TBT, TBT-resistant cells made up as much as 50% of the population. For non-coated stainless steel surfaces, Cu-resistant cells initially made up the majority of the population, but after 48 h they made up less than 1% of the population. On Cu-coated stainless steel, Cu-resistant cells predominated through 48 h, but after 48 h they comprised less than 10% of the population. These results suggest that the growth of TBT-resistant and Cu-resistant cells contributes to biofilms of P. aeruginosa PAO-1 at early stages of development but not at later stages. Received 16 December 1997/ Accepted in revised form 9 March 1998     

Biofilms in drinking water systems: a possible reservoir for Helicobacter pylori

A laboratory model system was utilised to investigate the persistence of Helicobacter pylori in mixed-species heterotrophic biofilms. A single-stage continuous culture vessel was linked to a modified-Robbins device (mRD) incorporating removable stainless steel coupons. The system was innoculated with H. pylori (NCTC 11637) and the fate of the organism monitored by polymerase chain reaction (PCR) analysis. Helicobacter pylori was detected in biofilm material for a period of up to 192 h. Theoretical washout would have occurred at around 48 h thus detection of H. pylori for a prolonged period after theoretical washout suggested that the organism possessed the ability to persist in the mixed-species heterotrophic biofilm. Preliminary studies using heat-inactivated H. pylori showed that the organism was not detected in biofilm material at any time post-challenge suggesting that the persistence of H. pylori in such material was a phenomenon requiring the organism to be in a viable state. Further investigations to assess the biological basis for the association of H. pylori with drinking water biofilms and the risk that this may pose to public health are being undertaken.     

Influence of pipe materials and VBNC cells on culturable bacteria in a chlorinated drinking water model system

To elucidate the influence of pipe materials on the VBNC (viable but nonculturable) state and bacterial numbers in drinking water, biofilm and effluent from stainless steel, galvanized iron, and polyvinyl chloride pipe wafers were analyzed. Although no HPC (heterotrophic plate count) was detected in the chlorinated influent of the model system, a DVC (direct viable count) still existed in the range between 3- and 4-log cells/ml. Significantly high numbers of HPC and DVC were found both in biofilm and in the effluent of the model system. The pipe material, exposure time, and the season were all relevant to the concentrations of VBNC and HPC bacteria detected. These findings indicate the importance of determining the number of VBNC cells and the type of pipe materials to estimate the HPC concentration in water distribution systems and thus the need of determining a DVC in evaluating disinfection efficiency.     

Nonuniform spatial patterns of respiratory activity within biofilms during disinfection.

Fluorescent stains in conjunction with cryoembedding and image analysis were applied to demonstrate spatial gradients in respiratory activity within bacterial biofilms during disinfection with monochloramine. Biofilms of Klebsiella pneumoniae and Pseudomonas aeruginosa grown together on stainless steel surfaces in continuous-flow annular reactors were treated with 2 mg of monochloramine per liter (influent concentration) for 2 h. Relatively little biofilm removal occurred as evidenced by total cell direct counts. Plate counts (of both species summed) indicated an average 1.3-log decrease after exposure to 2 mg of monochloramine per liter. The fluorogenic redox indicator 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) and the DNA stain 4',6-diamidino-2-phenylindole (DAPI) were used to differentiate respiring and nonrespiring cells in biofilms. Epifluorescence micrographs of frozen biofilm cross sections clearly revealed gradients of respiratory activity within biofilms in response to monochloramine treatment. These gradients in specific respiratory activity were quantified by calculating the ratio of CTC and DAPI intensities measured by image analysis. Cells near the biofilm-bulk fluid interface lost respiratory activity first. After 2 h of biocide treatment, greater respiratory activity persisted deep in the biofilm than near the biofilm-bulk fluid interface.     

Inactivation of Escherichia coli, Listeria monocytogenes, Pseudomonas aeruginosa and Staphylococcus aureus on stainless steel and glass surfaces by neutral electrolysed water

AIM: To ascertain the efficacy of neutral electrolysed water (NEW) in reducing Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Listeria monocytogenes on glass and stainless steel surfaces. Its effectiveness for that purpose is compared with that of a sodium hypochlorite (NaClO) solution with similar pH, oxidation-reduction potential (ORP) and active chlorine content. METHODS AND RESULTS: First, the bactericidal activity of NEW was evaluated over pure cultures (8.5 log CFU ml-1) of the abovementioned strains: all of them were reduced by more than 7 log CFU ml-1 within 5 min of exposure either to NEW (63 mg l-1 active chlorine) or to NaClO solution (62 mg l-1 active chlorine). Then, stainless steel and glass surfaces were inoculated with the same strains and rinsed for 1 min in either NEW, NaClO solution or deionized water (control). In the first two cases, the populations of all the strains decreased by more than 6 log CFU 50 cm-2. No significant difference (P相似文献   

Attachment and biofilm formation on stainless steel by Escherichia coli O157:H7 as affected by curli production

AIMS: The aim of this study was to determine the role of curli in attachment and biofilm formation by Escherichia coli O157:H7 on stainless steel. METHODS AND RESULTS: Three curli-deficient strains (43895-, 43894- and E0018-) and three curli over-producing strains (43895+, 43894+ and E0018+) of E. coli O157:H7 were studied. Stainless steel coupons (SSC) were immersed in cell suspensions of each strain for 24 h at 4 degrees C. The number of cells attached to SSC was determined. To determine the ability of attached cells to form biofilm, SSC were immersed in 10% of tryptic soya broth up to 6 days at 22 degrees C. Curli-deficient and curli-producing strains did not differ in their ability to attach to SSC, but only curli-producing strains formed biofilms. CONCLUSIONS: Curli production by E. coli O157:H7 does not affect attachment of cells on stainless steel but curli-producing strains are better able to form biofilms. SIGNIFICANCE AND IMPACT OF THE STUDY: Curli production by E. coli O157:H7 enhances its ability to form biofilm on stainless steel, thereby potentially resulting in increased difficulty in removing or killing cells by routine cleaning and sanitizing procedures used in food-processing plants.     

Colorimetric assay for biofilms in wet processing conditions

Controlling bacterial biofilms is necessary for food safety and industrial processing in clean room environments. Our goal was to develop a method to quantitatively measure biofilm produced by pathogens under wet poultry production and processing conditions. Stainless steel and glass coupons were incubated in aqueous media containing reduced nutrients and exposed to Listeria monocytogenes under static temperature and humidity conditions. Samples were measured separately by biofilm assay and viable cell density, and then confirmed by spectrophotometry and microscopy. The biofilm assay resulted in different t groupings from the cell density. The mean from the biofilm assay was 0.50, and the error% was 0.595. The mean of the log₁₀ density (cfu/cm²) was 5.90, and the standard deviation ranged from 0.127 to 0.438 on 24 coupons. The typical sequence of biofilm development, followed by microscopy of biofilm grown on glass coupons, exhibited a change from dispersed single cells to an all-over pattern of clumps with few dispersed cells. L. monocytogenes formed biofilms on all of the substrata tested. Bacterial counts from planktonic cultures at 24, 48, 72, and 144 h confirmed that L. monocytogenes remained viable throughout the experiment and reached equilibrium between 6 and 24 h. The cell density log₁₀/ml was 8.01, 8.03, 7.69, and 6.66, respectively; and the standard deviation ranged from 0.156 to 0.394. The data will be used to grow stable biofilms of Listeria spp. collected from the food processing environment for further study. This is the first use of the crystal violet assay for measurement of bacterial biofilms on stainless steel under these conditions. The methods tested are applicable to other bacteria and substrata.     

Combining chlorination and chloramination processes for the inhibition of biofilm formation in drinking surface water system models

AIMS: The aim of this study was to investigate the inhibition of biofilm formation on stainless steel (SS) and galvanized mild steel (MS) in chlorine (AFC(1)) and chlorine-monochloramine treated waters (AFC(2)M). METHODS AND RESULTS: Disinfection was carried out using 2.5 mg l(-1) free chlorine followed by 1.5 mg l(-1) monochloramine, with non-disinfected water used as control water. Results of the standard spread plate procedure, DAPI epifluorescence microscopy and scanning electron microscopy revealed bacterial colonization of SS and MS exposed to non-disinfected and chlorinated waters between 24 and 720 h, while no bacterial adhesion was detected on SS and MS exposed to AFC(2)M between 48 and 504 h. CONCLUSIONS: The inability of bacteria to grow on SS and MS was observed only when 0.35 mg l(-1) residual monochloramine was maintained throughout the system. SIGNIFICANCE AND IMPACT OF THE STUDY: This demonstrates the inability of chlorine alone to inhibit bacterial growth and suggests a combination of chlorine and monochloramine as a more effective treatment for drinking water, especially for rural communities with very poor source waters in Africa.     

Survival of Yersinia pestis on environmental surfaces

The survival of two strains of Yersinia pestis (avirulent A1122 and virulent Harbin) on the surfaces of four materials was investigated. Viability was evaluated with epifluorescence microscopy by using the metabolic stain cyanoditolyl tetrazolium chloride and plate counts. Small numbers of cells suspended in phosphate buffer survived 2 to 4 h after visible drying on stainless steel, polyethylene, or glass and beyond 48 h on paper. Cells suspended in brain heart infusion broth (BHI) persisted more than 72 h on stainless steel, polyethylene, and glass. Small numbers of cells suspended in BHI were still viable at 120 h on paper. These data suggest that Y. pestis maintains viability for extended periods (last measured at 5 days) under controlled conditions.     

A direct viable count method for the enumeration of attached bacteria and assessment of biofilm disinfection

This report describes the adaptation of an in situ direct viable count (in situ DVC) method in biofilm disinfection studies. The results obtained with this technique were compared to two other enumeration methods, the plate count (PC) and conventional direct viable count (c-DVC). An environmental isolate (Klebsiella pneumoniae Kp1) was used to form biofilms on stainless steel coupons in a stirred batch reactor. The in situ DVC method was applied to directly assess the viability of bacteria in biofilms without disturbing the integrity of the interfacial community. As additional advantages, the results were observed after 4 h instead of the 24 h incubation time required for colony formation and total cell numbers that remained on the substratum were enumerated. Chlorine and monochloramine were used to determine the susceptibilities of attached and planktonic bacteria to disinfection treatment using this novel analytical approach. The planktonic cells in the reactor showed no significant change in susceptibility to disinfectants during the period of biofilm formation. In addition, the attached cells did not reveal any more resistance to disinfection than planktonic cells. The disinfection studies of young biofilms indicated that 0.25 mg/l free chlorine (at pH 7.2) and 1 mg/l monochloramine (at pH 9.0) have comparable disinfection efficiencies at 25 degrees C. Although being a weaker disinfectant, monochloramine was more effective in removing attached bacteria from the substratum than free chlorine. The in situ DVC method always showed at least one log higher viable cell densities than the PC method, suggesting that the in situ DVC method is more efficient in the enumeration of biofilm bacteria. The results also indicated that the in situ DVC method can provide more accurate information regarding the cell numbers and viability of bacteria within biofilms following disinfection.     

Antimicrobial Efficacy of Surface-Coated External Fixation Pins

In clinical applications, colonization of metal implants by adhesive and biofilm-forming bacteria not only prolong healing but create additional healthcare costs for implant revision and antimicrobial treatment. An in vitro assay was established investigating the antimicrobial surface activity of external fixation pins intended for use in bone fractures and deformities. Test articles made out of stainless steel and coated with a polymer-containing nanoparticulate silver were compared to non-coated reference controls out of stainless steel, copper and titanium. Staphylococcus epidermidis, known as a predominant cause for implant-related infections was used as test organism. Test pins and bacteria were incubated for a period of 20 h found to be sufficient for initiating biofilm formation. After removing non- and low-adherent bacteria by rinsing, two methods were used to isolate high-adherent (sessile) bacteria from the implant surfaces. Besides shaking the implants in a solution containing small glass beads, a cytobrush technique was used to mechanically harvest viable bacteria. Finally, the amount of detached bacteria was determined by plate counts. Several parameters identified to be critical within the different removal procedures such as the inoculum concentration and the shaking time in the presence of glass beads as well as time of the cytobrush treatment were analysed. The final test scheme resulted in the use of an inoculum of 10⁵ colony forming units (CFU) per millilitre, ten rinsing steps for the removal of low adherent bacteria and 5 min of shaking in the presence of glass beads, detaching the high-adherent bacteria. Due to subjective variations impacting the outcome of the procedure, the cytobrush technique was not favoured and finally rejected. Using the in vitro assay developed, it could be demonstrated that fixation pins coated with silver show a 3 log step reduction in the number of biofilm-forming bacteria compared to a non-coated stainless steel or titanium implant. Pins made out of copper showed the highest antimicrobial efficacy, as the number of detached bacteria was found to be below the detection limit, they served as a positive control within this test.     

Air-liquid interface biofilms of Bacillus cereus: formation, sporulation, and dispersion

Biofilm formation by Bacillus cereus was assessed using 56 strains of B. cereus, including the two sequenced strains, ATCC 14579 and ATCC 10987. Biofilm production in microtiter plates was found to be strongly dependent on incubation time, temperature, and medium, as well as the strain used, with some strains showing biofilm formation within 24 h and subsequent dispersion within the next 24 h. A selection of strains was used for quantitative analysis of biofilm formation on stainless steel coupons. Thick biofilms of B. cereus developed at the air-liquid interface, while the amount of biofilm formed was much lower in submerged systems. This suggests that B. cereus biofilms may develop particularly in industrial storage and piping systems that are partly filled during operation or where residual liquid has remained after a production cycle. Moreover, depending on the strain and culture conditions, spores constituted up to 90% of the total biofilm counts. This indicates that B. cereus biofilms can act as a nidus for spore formation and subsequently can release their spores into food production environments.     

Factors influencing attachment of thermophilic bacilli to stainless steel

AIMS: This project aimed to investigate the mechanism of attachment of the vegetative cells and spores of thermophilic bacilli to stainless steel with a view to devising strategies to limit biofilm development and survival. METHODS AND RESULTS: Spores and vegetative cells of bacterial isolates were exposed to protein denaturing agents (sodium dodecyl sulphate (SDS) and trypsin) and polysaccharide removing agents (sodium metaperiodate, trichloroacetic acid (TCA) and lysozyme). Treatment with sodium metaperiodate, TCA and lysozyme increased the number of vegetative cells attaching in many of the strains studied, while SDS and trypsin decreased attachment. Spores attached to stainless steel in greater numbers than vegetative cells, and the various treatments had less effect on this attachment than for vegetative cells. Viability of the cells or spores was not an important factor in attachment, as cells and spores rendered non-viable also attached to stainless steel in similar numbers. Coating the stainless steel with skim milk proteins decreased the attachment of both vegetative cells and spores. There was no correlation between the degree of attachment and the amount of extracellular polysaccharide (EPS) produced by each strain, surface hydrophobicity or zeta potential of vegetative cells or spores, though spores were found to be more hydrophobic than vegetative cells. CONCLUSIONS: The results suggest that biofilm formation by these thermophilic bacilli is probably a multifactorial process, and that cell-surface proteins play a very important role in the initial process of attachment during the formation of biofilms by these bacteria. SIGNIFICANCE AND IMPACT OF THE STUDY: This information will provide direction for developing improved cleaning systems to control biofilms of thermophilic bacilli in dairy manufacturing plants.     

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

AIMS: To determine the differential adherence capabilities at three different temperatures of Listeria monocytogenes Scott A, a clinical food pathogen, and L. monocytogenes FM876, a persistent strain from a milk-processing environment, to stainless steel. METHODS AND RESULTS: Differential adherence was investigated by submerging stainless steel coupons in both 48-h Listeria monocultures and mixed cultures additionally containing Staphylococcus xylosus DP5H and Pseudomonas fragi ATCC 4973. Immunofluorescent microscopy and image analysis techniques were utilized to identify and quantify the L. monocytogenes cells adhering to the steel at 4 degrees C, 18 degrees C and 30 degrees C. The monoculture biofilms consistently contained greater L. monocytogenes numbers than the multispecies biofilms, with the persistent strain FM876 showing significantly greater adherence than strain Scott A. Optimum adherence occurred at 18 degrees C in monoculture biofilms. CONCLUSION: L. monocytogenes strains exhibit differential, temperature-dependent, adherence to stainless steel. SIGNIFICANCE AND IMPACT OF THE STUDY: These results demonstrate temperature dependent biofilm adherence and support previous findings that persistent strains exhibit increased adherence capability.     

Survival of Yersinia pestis on Environmental Surfaces

The survival of two strains of Yersinia pestis (avirulent A1122 and virulent Harbin) on the surfaces of four materials was investigated. Viability was evaluated with epifluorescence microscopy by using the metabolic stain cyanoditolyl tetrazolium chloride and plate counts. Small numbers of cells suspended in phosphate buffer survived 2 to 4 h after visible drying on stainless steel, polyethylene, or glass and beyond 48 h on paper. Cells suspended in brain heart infusion broth (BHI) persisted more than 72 h on stainless steel, polyethylene, and glass. Small numbers of cells suspended in BHI were still viable at 120 h on paper. These data suggest that Y. pestis maintains viability for extended periods (last measured at 5 days) under controlled conditions.