Cleanability in relation to bacterial retention on unused and abraded domestic sink materials

The relative cleanability of stainless steel, enamelled steel, mineral resin and polycarbonate domestic sink materials was assessed by comparing the number of organisms remaining on surfaces after cleaning. In unused condition all materials, other than one enamelled steel, were equally cleanable. Stainless steel, abraded artificially or impact damaged to a similar degree as stainless steel subjected to domestic wear, retained approximately one log order less bacteria after cleaning than the other materials subjected to the same treatments. Little difference in cleanability was recorded between the abraded surfaces of the other materials although enamelled steel surfaces were less cleanable than mineral resin or polycarbonate after impact damage, because of the greater susceptibility of enamelled steel to damage by this treatment. When cleaning time was extended beyond 10 s for the abraded and impact damaged materials, their cleanability was not enhanced as compared with stainless steel. Changes in surface finish after abrasion were assessed by surface roughness measurement and scanning electron microscopy. Surfaces with poor cleanability before and after abrasion were characterized by pitting, crevices or jags. These surfaces are likely to retain more bacteria because of increased numbers of attachment sites, a larger bacterial/material surface contact area and topographical areas in which applied cleaning shear forces are reduced. Materials that resist surface changes, e.g. stainless steel, will remain more hygienic when subjected to natural wear than materials which become more readily damaged.     

Cleanability in relation to bacterial retention on unused and abraded domestic sink materials

H olah , J.T. & T horpe , R.H. 1990. Cleanability in relation to bacterial retention on unused and abraded domestic sink materials. Journal of Applied Bacteriology 69 , 599–608.
The relative Cleanability of stainless steel, enamelled steel, mineral resin and polycarbonate domestic sink materials was assessed by comparing the number of organisms remaining on surfaces after cleaning. In unused condition all materials, other than one enamelled steel, were equally cleanable. Stainless steel, abraded artificially or impact damaged to a similar degree as stainless steel subjected to domestic wear, retained approximately one log order less bacteria after cleaning than the other materials subjected to the same treatments. Little difference in Cleanability was recorded between the abraded surfaces of the other materials although enamelled steel surfaces were less cleanable than mineral resin or polycarbonate after impact damage, because of the greater susceptibility of enamelled steel to damage by this treatment. When cleaning time was extended beyond 10 s for the abraded and impact damaged materials, their Cleanability was not enhanced as compared with stainless steel. Changes in surface finish after abrasion were assessed by surface roughness measurement and scanning electron microscopy. Surfaces with poor Cleanability before and after abrasion were characterized by pitting, crevices or jags. These surfaces are likely to retain more bacteria because of increased numbers of attachment sites, a larger bacterial/material surface contact area and topographical areas in which applied cleaning shear forces are reduced. Materials that resist surface changes, e.g. stainless steel, will remain more hygienic when subjected to natural wear than materials which become more readily damaged.     

Adhesion and removal kinetics of Bacillus cereus biofilms on Ni-PTFE modified stainless steel

Biofilm control remains a challenge to food safety. A well-studied non-fouling coating involves codeposition of polytetrafluoroethylene (PTFE) during electroless plating. This coating has been reported to reduce foulant build-up during pasteurization, but opportunities remain in demonstrating its efficacy in inhibiting biofilm formation. Herein, the initial adhesion, biofilm formation, and removal kinetics of Bacillus cereus on Ni-PTFE-modified stainless steel (SS) are characterized. Coatings lowered the surface energy of SS and reduced biofilm formation by > 2 log CFU cm^?2. Characterization of the kinetics of biofilm removal during cleaning demonstrated improved cleanability on the Ni-PTFE coated steel. There was no evidence of biofilm after cleaning by either solution on the Ni-PTFE coated steel, whereas more than 3 log and 1 log CFU cm^?2 of bacteria remained on the native steel after cleaning with water and an alkaline cleaner, respectively. This work demonstrates the potential application of Ni-PTFE non-fouling coatings on SS to improve food safety by reducing biofilm formation and improving the cleaning efficiency of food processing equipment.     

Processes of bioadhesion on stainless steel surfaces and cleanability: A review with special reference to the food industry

Biofouling of equipment surfaces in the food industry is due initially to physico-chemical adhesion processes, and subsequently to the proliferation of microbes within an extracellular polymer matrix. Two physico-chemical theories can be applied to predict simple cases of bacterial adhesion. However, these models are limited in their applicability owing to the complexity of bacterial surfaces and the surrounding medium. Various factors that can affect the bacterial adhesion process have been listed, all directly linked to the solid substratum, the suspension liquid or the microorganism. For stainless steel surfaces, it is important to take into account the grade of steel, the type of finish, surface roughness, the cleaning procedures used and the age of the steel. Regarding the suspension fluid within which adhesion takes place, pH, ionic composition and the presence of macromolecules are important variables. In addition, the adhering microorganisms have extremely complex surfaces and many factors must be taken into account when conducting adhesion tests, such as the presence of cell appendages, the method of culture, the contact time between the microorganism and the surface, and exopolymer synthesis. Research on biofilms growing on stainless steel has confirmed results obtained with other materials, regarding resistance to disinfectants, the role of the extracellular matrix and the process by which the biofilm forms. However, it appears that the bactericidal activity of disinfectants on biofilms differs according to the type of surface on which they are growing. The main cleaners and disinfectants used in the food industry are alkaline and acid detergents, peracetic acid, quaternary ammonium chlorides and iodophors. The cleanability and disinfectability of stainless steel surfaces have been compared with those of other materials. According to the published research findings, stainless steel is comparable in its biological cleanability to glass, and significantly better than polymers, aluminium or copper. Moreover, microorganisms in a biofilm developing on a stainless steel surface can be killed with lower concentrations of disinfectant than those on polymer surfaces.     

Bacterial Community Structure of Biofilms on Artificial Surfaces in an Estuary

This study examined bacterial community structure of biofilms on stainless steel and polycarbonate in seawater from the Delaware Bay. Free-living bacteria in the surrounding seawater were compared to the attached bacteria during the first few weeks of biofilm growth. Surfaces exposed to seawater were analyzed by using 16S rDNA libraries, fluorescence in situ hybridization (FISH), and denaturing gradient gel electrophoresis (DGGE). Community structure of the free-living bacterial community was different from that of the attached bacteria according to FISH and DGGE. In particular, alpha-proteobacteria dominated the attached communities. Libraries of 16S rRNA genes revealed that representatives of the Rhodobacterales clade were the most abundant members of biofilm communities. Changes in community structure during biofilm growth were also examined by DGGE analysis. We hypothesized that bacterial communities on dissimilar surfaces would initially differ and become more similar over time. In contrast, the compositions of stainless steel and polycarbonate biofilms were initially the same, but differed after about 1 week of biofilm growth. These data suggest that the relationship between surface properties and biofilm community structure changes as biofilms grow on surfaces such as stainless steel and polycarbonate in estuarine water.     

A comparative evaluation with respect to the bacterial cleanability of a range of wall and floor surface materials used in the food industry

J. H. TAYLOR AND J. T. HOLAH. 1996. A range of floor and wall materials suitable for use in the food industry were selected for comparative bacterial cleanability tests. A standard cleaning regime was carried out on samples after biofilm development of Acinetobacter calcoaceticus (CRA 296). Cleanability was measured as the log reduction in bacterial numbers. The results for the wall materials showed that there were no statistical differences, whilst those for the floor materials were more variable. The grouted joints and texture did not compromise the cleanabilities of tiled surfaces.     

2种不同器械扩锉后根管壁的细菌学研究

目的通过对临床病例的研究,比较减速镍钛机扩和普通不锈钢K型锉清洁根管的能力。方法选取临床需要根管治疗的患牙60例,随机分为2组,经开髓拨髓后分别用镍钛减速机扩和不锈钢K型及H型锉进行根管预备,预备完成后用灭菌棉捻擦拭管壁,作微生物检查。结果2组方法扩锉后对根管内微生物的变化做统计学分析,差异有显著性(P<0.05)。结论镍钛减速机扩对根管的清洁能力高于普通不锈钢扩锉,值得临床的推广。     

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 influence of milk and milk components on the attachment of bacteria to farm dairy equipment surfaces

Glass, rubber and stainless steel surfaces were exposed to various types of bacteria in the presence of milk and a number of milk components under both static and agitated incubation conditions. Numbers of bacteria attaching were enumerated by epifluorescence microscopy. Results were affected by the different bacterial types, the nature of the attachment surface and the substances in which the bacteria were suspended with a Moraxella -like species, stainless steel and lactose and non-casein protein solutions respectively resulting in greatest numbers of cells attaching. Agitation had no marked influence on attachment.     

Biomolecules in multilayer film for antimicrobial and easy-cleaning stainless steel surface applications

Microorganisms are able to attach to, grow on, and ultimately form biofilms on a large variety of surfaces, such as industrial equipment, food contact surfaces, medical implants, prostheses and operating rooms. Once organized into biofilms, bacteria are difficult to remove and kill, which increases the risk of cross-contamination and infection. One way to address the problem may thus be to develop antibacterial, anti-adhesion, ‘easy cleaning’ surfaces. In this study, stainless steel (SS) surfaces with antibacterial properties were created by embedding several antimicrobial peptides in a multilayer film architecture. The biocidal effect of these surfaces was demonstrated against both Gram-positive and Gram-negative bacteria according to two ISO tests. Also, coating SS surfaces with either mucin or heparin led to a reduction of S. epidermidis adhesion of almost 95% vs the bare substratum. Finally, by combining both antibacterial and anti-adhesion biomolecules in the same multilayer film, SS surfaces with better cleanability were produced. This surface coating property may help to delay the buildup of a dead bacterial layer which is known to progressively reduce exposure of the coating, leading to an undesirable decrease in the antibacterial effect of the surface.     

Biofilm retention on surfaces with variable roughness and hydrophobicity

Biofilms on food processing equipment cause food spoilage and pose a hazard to consumers. The bacterial community on steel surfaces in a butcher's shop was characterized, and bacteria representative of this community enriched from minced pork were used to study biofilm retention. Stainless steel (SS) was compared to two novel nanostructured sol-gel coatings with differing hydrophobicity. Surfaces were characterized with respect to roughness, hydrophobicity, protein adsorption, biofilm retention, and community composition of the retained bacteria. Fewer bacteria were retained on the sol-gel coated surfaces compared to the rougher SS. However, the two sol-gel coatings did not differ in either protein adsorption, biofilm retention, or microbial community composition. When polished to a roughness similar to sol-gel, the SS was colonized by the same amount of bacteria as the sol-gel, but the bacterial community contained fewer Pseudomonas cells. In conclusion, biofilm retention was affected more by surface roughness than chemical composition under the condition described in this study.     

Determination of abundance and biovolume of bacteria in sediments by dual staining with 4',6-diamidino-2-phenylindole and acridine orange: relationship to dispersion treatment and sediment characteristics.

We measured the abundance and biovolume of bacteria in intertidal sediments from Tokyo Bay, Japan, by using a dual-staining technique (4',6-diamidino-2-phenylindole and acridine orange) and several dispersion techniques (ultrasonic cleaner, ultrasonic sonicator, and tissue homogenizer). Dual staining reduced serious background fluorescence, particularly when used for silt-, clay-, and detritus-rich sediments, and allowed us to distinguish bacteria from other objects during both counting and sizing. Within the studied samples, the number of bacterial cells ranged from 0.20 x 10(9) to 3. 54 x 10(9) g of wet sediment(-1). With the cleaner and sonicator treatments, the bacterial numbers for all of the sites initially increased with dispersion time and then became constant. For the homogenizer treatments, the highest bacterial numbers were observed with the shortest (0.5- to 2-min) treatments, and the counts then declined steeply as the homogenization time increased, indicating that cell destruction occurred. The cleaner treatment had the possibility of insufficient dispersion of bacteria for fine-grain sediments. Within the studied samples, the bacterial biovolume ranged from 0.07 to 0.22 microm(3). With the cleaner and sonicator treatments, the biovolume peaked during the shorter dispersion time. This pattern was caused not by cell destruction but by the incremental portion of dispersed small cells. We concluded that with the cleaner and sonicator treatments, the longer dispersion time reflected the real size spectrum and was preferable for accurate estimation of mean bacterial biovolumes.     

Retention of the Gram-negative bacterium SW8 on surfaces under conditions relevant to the subsurface environment: Effects of conditioning films and substratum nature

Abstract Shallow (5–13 m) and deep (35–65 m) groundwaters were evaluated for their ability to generate conditioning films which affect bacterial adhesion to natural (sandstone, shale, andesite) and man-made substrata (polypropylene, stainless steel). Water contact angles indicated that all water samples produced conditioning films. Most films modified retention of the nonmotile Gram-negative bacterium SW8, but attachment of the organism did not correlate with water contact angles. Each borewater produced conditioning films with a characteristic attachment profile of SW8. Films adsorbed from standing borewaters often retained SW8 in different numbers than coatings derived from pumped bores. Groundwater chemistry was very heterogeneous and microbiological data indicated the presence of a diverse aerobic and anaerobic microbial community. These results indicate that conditioning films derived from dissolved compounds may play a significant role in controlling the interaction of bacteria with substrata in the subsurface.     

Effectiveness of disinfectants in killing Enterobacter sakazakii in suspension, dried on the surface of stainless steel, and in a biofilm

The effectiveness of 13 disinfectants used in hospitals, day-care centers, and food service kitchens in killing Enterobacter sakazakii in suspension, dried on the surface of stainless steel, and in biofilm was determined. E. sakazakii exhibited various levels of resistance to the disinfectants, depending on the composition of the disinfectants, amount and type of organic matrix surrounding cells, and exposure time. Populations of planktonic cells suspended in water (7.22 to 7.40 log CFU/ml) decreased to undetectable levels (<0.30 log CFU/ml) within 1 to 5 min upon treatment with disinfectants, while numbers of cells in reconstituted infant formula were reduced by only 0.02 to 3.69 log CFU/ml after the treatment for 10 min. The presence of infant formula also enhanced the resistance to the disinfectants of cells dried on the surface of stainless steel. The resistance of cells to disinfectants in 6-day-old and 12-day-old biofilms on the surface of stainless steel was not significantly different. The overall order of efficacy of disinfectants in killing E. sakazakii was planktonic cells > cells inoculated and dried on stainless steel > cells in biofilms on stainless steel. Findings show that disinfectants routinely used in hospital, day-care, and food service kitchen settings are ineffective in killing some cells of E. sakazakii embedded in organic matrices.     

Influence of copper-alloying of austenitic stainless steel on multi-species biofilm development

AIMS: To investigate the bactericidal influence of copper-alloying of stainless steel on microbial colonization. METHODS AND RESULTS: Inhibition of bacterial adherence was investigated by monitoring (192 h) the development of a multi-species biofilm on Cu-alloyed (3.72 wt%) stainless steel in a natural surface water. During the first 120 h of exposure, lower numbers of viable bacteria in the water in contact with copper-containing steel relative to ordinary stainless steel were observed. Moreover, during the first 48 h of exposure, lower colony counts were found in the biofilm adhering to the Cu-alloyed steel. No lower colony or viable counts were found throughout the remainder of the experimental period. CONCLUSION: The presence of Cu in the steel matrix impedes the adhesion of micro-organisms during an initial period (48 h), while this bactericidal effect disappears after longer incubation periods. SIGNIFICANCE AND IMPACT OF THE STUDY: The application of Cu-alloyed stainless steels for bactericidal purposes should be restricted to regularly-cleaned surfaces.     

Determination of Abundance and Biovolume of Bacteria in Sediments by Dual Staining with 4′,6-Diamidino-2-Phenylindole and Acridine Orange: Relationship to Dispersion Treatment and Sediment Characteristics

We measured the abundance and biovolume of bacteria in intertidal sediments from Tokyo Bay, Japan, by using a dual-staining technique (4′,6-diamidino-2-phenylindole and acridine orange) and several dispersion techniques (ultrasonic cleaner, ultrasonic sonicator, and tissue homogenizer). Dual staining reduced serious background fluorescence, particularly when used for silt-, clay-, and detritus-rich sediments, and allowed us to distinguish bacteria from other objects during both counting and sizing. Within the studied samples, the number of bacterial cells ranged from 0.20 × 10⁹ to 3.54 × 10⁹ g of wet sediment⁻¹. With the cleaner and sonicator treatments, the bacterial numbers for all of the sites initially increased with dispersion time and then became constant. For the homogenizer treatments, the highest bacterial numbers were observed with the shortest (0.5- to 2-min) treatments, and the counts then declined steeply as the homogenization time increased, indicating that cell destruction occurred. The cleaner treatment had the possibility of insufficient dispersion of bacteria for fine-grain sediments. Within the studied samples, the bacterial biovolume ranged from 0.07 to 0.22 μm³. With the cleaner and sonicator treatments, the biovolume peaked during the shorter dispersion time. This pattern was caused not by cell destruction but by the incremental portion of dispersed small cells. We concluded that with the cleaner and sonicator treatments, the longer dispersion time reflected the real size spectrum and was preferable for accurate estimation of mean bacterial biovolumes.     

Inactivation of Escherichia coli O157:H7 in biofilm on stainless steel by treatment with an alkaline cleaner and a bacteriophage

AIMS: To determine the effectiveness of an alkaline cleaner used in food-processing plants and a lytic bacteriophage specific for Escherichia coli O157:H7 in killing wild type and rpoS-deficient cells of the pathogen in a biofilm. METHODS AND RESULTS: Wild type and rpoS-deficient cells were attached to stainless steel coupons (c. 7-8 log CFU per coupon) on which biofilms were developed during incubation at 22 degrees C for 96 h in M9 minimal salts media (MSM) with one transfer to fresh medium. Coupons were treated with 100 and 25% working concentrations of a commercial alkaline cleaner (pH 11.9, with 100 microg ml(-1) free chlorine) used in the food industry, chlorine solutions (50 and 100 microg ml(-1) free chlorine), or sterile deionized water (control) at 4 degrees C for 1 and 3 min. Treatment with 100% alkaline cleaners reduced populations by 5-6 log CFU per coupon, a significant (P < or = 0.05) reduction compared with treatment with water. Initial populations (2.6 log CFU per coupon) of attached cells of both strains were reduced by 1.2 log CFU per coupon when treated with bacteriophage KH1 (7.7 log PFU ml(-1)) for up to 4 days at 4 degrees C. Biofilms containing low populations (2.7-2.8 log CFU per coupon) of wild type and rpoS-deficient cells that had developed for 24 h at 22 degrees C were not decreased by more than 1 log CFU per coupon when treated with KH1 (7.5 log PFU ml(-1)) at 4 degrees C. CONCLUSIONS: Higher numbers of cells of E. coli O157:H7 in biofilms are killed by treatment with an alkaline cleaner than with hypochlorite alone, possibly through a synergistic mechanism of alkaline pH and hypochlorite. Populations of cells attached on coupons were reduced by treating with bacteriophage but cells enmeshed in biofilms were protected. SIGNIFICANCE AND IMPACT OF THE STUDY: The alkaline pH, in combination with hypochlorite, in a commercial cleaner is responsible for killing E. coli O157:H7 in biofilms. Treatment with bacteriophage KH1 reduces populations of cells attached to coupon surfaces but not cells in biofilms.     

Effect of milk proteins on adhesion of bacteria to stainless steel surfaces.

Stainless steel coupons were treated with skim milk and subsequently challenged with individual bacterial suspensions of Staphylococcus aureus, Pseudomonas fragi, Escherichia coli, Listeria monocytogenes, and Serratia marcescens. The numbers of attached bacteria were determined by direct epifluorescence microscopy and compared with the attachment levels on clean stainless steel with two different surface finishes. Skim milk was found to reduce adhesion of S. aureus, L. monocytogenes, and S. marcescens. P. fragi and E. coli attached in very small numbers to the clear surfaces, making the effect of any adsorbed protein layer difficult to assess. Individual milk proteins alpha-casein, beta-casein, kappa-casein, and alpha-lactalbumin were also found to reduce the adhesion of S. aureus and L. monocytogenes. The adhesion of bacteria to samples treated with milk dilutions up to 0.001% was investigated. X-ray photoelectron spectroscopy was used to determine the proportion of nitrogen in the adsorbed films. Attached bacterial numbers were inversely related to the relative atomic percentage of nitrogen on the surface. A comparison of two types of stainless steel surface, a 2B and a no. 8 mirror finish, indicated that the difference in these levels of surface roughness did not greatly affect bacterial attachment, and reduction in adhesion to a milk-treated surface was still observed. Cross-linking of adsorbed proteins partially reversed the inhibition of bacterial attachment, indicating that protein chain mobility and steric exclusion may be important in this phenomenon.     

Evaluation of Disinfection Techniques for, and Their Effects on, Rectal Thermocouple Catheters

The antibacterial activities of an iodophor (Wescodyne G), a quaternary ammonium compound (Roccal), and an iodine tincture as agents for the cold disinfection of rectal catheters contaminated in vitro were determined. Following thorough cleaning with an alcoholic solution of soft soap, each of the three disinfectants tested showed satisfactory results (100% kill) in 5 min against the enteric test bacteria (Escherichia coli and Salmonella typhosa) as well as a test species of the genus Pseudomonas, among the bacteria most resistant to surface-active agents.

An aqueous solution of Wescodyne G containing 75 ppm available iodine was used both as a wiping solution and for subsequent disinfection of rectal catheters contaminated in vivo. Total bacterial destruction was found to follow a 60-min soak preceded by the wiping procedure.

Rectal catheters subjected to prolonged immersion in each of the test disinfectants were found to be essentially unaffected, retaining their initial calibrations within a permissible tolerance. Neither Roccal nor Wescodyne G solutions were found to measurably attack bare thermocouples. Alcoholic iodine 0.5% did, however, exert a deteriorating effect on bare thermocouples in a short time, as measured by change in resistance characteristics.

The results of this study have led to the recommendation that Wescodyne G containing 75 ppm available iodine be used in standing operating procedures for the initial cleaning and subsequent disinfection of rectal thermocouple catheters.

     

Acute impact of agriculture on high-affinity methanotrophic bacterial populations

Exposure of mineral soils to atmospherically relevant concentrations of ¹³CH₄ (2 ppmv) followed by ¹³C-phospholipid fatty acid stable isotope probing allows assessment of the high-affinity methanotrophic bacterial sink in hitherto unattainable detail. Utilizing this approach, inorganic fertilizer-treated soils from a long-term agricultural experiment were shown to display dramatic reduction, by > 70%, of the methanotrophic bacterial cell numbers. Reduction in the methane sink capacity of the soils was slightly lower than the directly observed reduction in methanotrophic bacterial counts, indicating that the inhibitory effects on high-affinity methanotrophic bacteria are not fully expressed through CH₄ oxidation rates. The results emphasize the need to rigorously assess commonly applied agricultural practices with respect to their unseen negative impacts on soil microbial diversity in relation to terrestrial sinks for atmospheric trace gases.