Effect of food residues on norovirus survival on stainless steel surfaces

Background

In households and food processing plants, minute food residues left behind from improper cleaning may influence the survivability of human norovirus on surfaces. In this study, the survivability of norovirus on desiccated food residue-attached stainless steel coupons was investigated.

Methodology/Principal Findings

Using murine norovirus-1 (MNV-1) as a surrogate of human norovirus, the survivability of norovirus was investigated on lettuce, cabbage, or ground pork-attached stainless steel coupons. A 6.2 log MPN/ml of MNV-1 infectivity was completely lost at day 30 in residue-free coupons, whereas only a 1.4 log MPN/ml reduction was observed in coupons with residues. Moreover, the disinfective effect of sodium hypochlorite was reduced when residues were present on the coupons.

Conclusions/Significance

This study revealed that the food residues increased the survivability and the resistance to chemicals of norovirus, indicating the need of thorough cleaning in food processing plants and household settings.     

Comparison of adhesion of the food spoilage bacterium Shewanella putrefaciens to stainless steel and silver surfaces

AIMS: To compare the number of attached Shewanella putrefaciens on stainless steel with different silver surfaces, thus evaluating whether silver surfaces could contribute to a higher hygienic status in the food industry. METHODS AND RESULTS: Bacterial adhesion to three types of silver surface (new silver, tarnished silver and sulphide-treated silver) was compared with adhesion to stainless steel (AISI 316) using the Malthus indirect conductance method to estimate the number of cfu cm(-2). The number of attached bacteria on new silver surfaces was lower than on steel for samples taken after 24 h. However, this was not statistically significant (P > 0.05). The numbers of attached bacteria were consistently lower when tarnished silver surfaces were compared with stainless steel and some, but not all, experiments showed statistical significance (P < 0.05). Treating new silver with sulphide to reproduce a tarnished silver surface did not result in a similar lowering of adhering cells when compared with steel (P > 0.05). CONCLUSIONS: New or tarnished silver surfaces caused a slight reduction in numbers of attached bacteria; however, the difference was only sometimes statistically significant. SIGNIFICANCE AND IMPACT OF THE STUDY: The lack of reproducibility in differences in numbers adhering to the different surfaces and lack of statistical significance between numbers of adhered viable bacteria do not indicate that the tested silver surfaces can be used to improve hygienic characteristics of surfaces in the food industry.     

Physico-chemical and hygienic property modifications of stainless steel surfaces induced by conditioning with food and detergent

The effect of repeated conditioning procedures (25 runs), consisting of soiling (milk and meat products) and cleaning steps, on the hygienic status, physico-chemical properties and surface chemical composition of stainless steel (SS) surfaces, was investigated. Five SSs differing in grade and finish were used. Both soiling and surface cleaning/conditioning procedures resulted in a similar increase in the surface contamination with carbon, while the changes in the basic component of the surface free energy depended on the conditioning procedure. The passive film was also affected, the Fe/Cr ratio in particular. The hygienic status was also changed, especially with milk as shown by monitoring the number of residual adhering Bacillus cereus spores after contaminating the surface with spores followed by cleaning. The results show that in food environments, the presence and the nature of conditioning molecules play a major role in the hygienic status of SS surfaces.     

Physico-chemical and hygienic property modifications of stainless steel surfaces induced by conditioning with food and detergent

The effect of repeated conditioning procedures (25 runs), consisting of soiling (milk and meat products) and cleaning steps, on the hygienic status, physico-chemical properties and surface chemical composition of stainless steel (SS) surfaces, was investigated. Five SSs differing in grade and finish were used. Both soiling and surface cleaning/conditioning procedures resulted in a similar increase in the surface contamination with carbon, while the changes in the basic component of the surface free energy depended on the conditioning procedure. The passive film was also affected, the Fe/Cr ratio in particular. The hygienic status was also changed, especially with milk as shown by monitoring the number of residual adhering Bacillus cereus spores after contaminating the surface with spores followed by cleaning. The results show that in food environments, the presence and the nature of conditioning molecules play a major role in the hygienic status of SS surfaces.     

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.     

Inactivation of influenza A virus on copper versus stainless steel surfaces

Influenza A virus particles (2 x 10(6)) were inoculated onto copper or stainless steel and incubated at 22 degrees C at 50 to 60% relative humidity. Infectivity of survivors was determined by utilizing a defined monolayer with fluorescent microscopy analysis. After incubation for 24 h on stainless steel, 500,000 virus particles were still infectious. After incubation for 6 h on copper, only 500 particles were active.     

Effect of methods of sterilization on thermoplastics with special reference to modified surfaces]

For materials intended for use in the medical setting their sterilizability is an indispensable prerequisite. In the case of most polymers the usual sterilization methods result in changes that even extend to cleavage of the polymer chains. A particular problem in this respect are the surfaces modified for improved biocompatibility investigated in the present study, which are characterised by enlarged contact areas. For this reason, possible changes to three different thermoplastics commonly used for medical applications (polyethylene, thermoplastic polyurethane, polycarbonate) were investigated. Steam, gas and radiation were used for sterilization. Tensile tests were employed to identify changes in mucosal characteristics caused by different sterilization techniques irrespective of the surface modification. Sterilization-related changes to the structure of the modified surfaces were investigated with the scanning electron microscope (SEM). Differential thermo analysis (DTA) was used to determine changes in the thermal characteristics of the plastics. Clear tendencies with regard to the behaviour of the plastics after sterilization with various techniques were found. A general statement about the compatibility of plastic materials with a specific sterilization method is not possible on the basis of this study. For every new polymeric product used for medical purposes, the characteristics required must first be defined and compliance with the permissible variations of these characteristics investigated for each of the various sterilization techniques available.     

Methodology for a comparative evaluation of sensitivity to fouling and cleanability of floor materials used in the food industry

Samples of floor materials used at present in different types of food plants were studied for their sensitivity to fouling and for their cleaning properties. A cleaning procedure close to that used in industry was carried out on seven different floor samples fouled with six industrial soils (e.g. green salad soil, reconstituted milk, and meat) and inoculated with spores of Bacillus stearothermophilus var. calidolactis as tracer. Sensitivity to fouling and the cleanability of the different floor materials were measured, and the results showed a significant difference between them. These differences were dependent upon the type of soil. Sensitivity to fouling and cleanability were not correlated with their slipping resistance characteristics.     

Non-inversion tillage and farmland birds: a review with special reference to the UK and Europe

This paper reviews the current knowledge of the effects of non-inversion tillage (NIT) on farmland birds and their food resources. NIT is a method of establishing a crop without using a mouldboard plough and is becoming increasingly popular in the UK. NIT generally disturbs the soil to shallower depths than conventional tillage and is therefore expected to have beneficial effects on biodiversity on arable land as compared with mouldboard ploughing. The diets of farmland birds change throughout the year, and many species take invertebrates over the breeding season. Seeds are also important for many species of farmland birds throughout the year and especially over the winter months. The effects of NIT on these farmland bird food resources, in particular ground beetles (Coleoptera: Carabidae), spiders (Arachnida: Araneae), earthworms (Annelida) and seeds (arable weeds and cereal crops) are reviewed.     

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.     

Butterflyfish social behaviour,with special reference to the incidence of territoriality: a review

Synopsis Butterflyfishes (Chaetodontidae) are among the best studied of coral reef fishes. Feeding ecology and some aspects of behaviour have been firmly established. However, spacing behaviour remains controversial. Two major studies made in the 1970s concluded that the majority of species were not territorial. We suggest that these and other studies which have concluded that territories are not held have generally suffered from short observation periods, and have not mapped the ranges occupied by individuals. Further, low frequencies of agonistic behaviour have been interpreted as evidence of non-territoriality. By contrast, studies which have proven territoriality have had long observation periods and have mapped ranges. These have shown that territories are usually maintained with very little overt aggression. Spacing behaviour and feeding behaviour are clearly linked, with territoriality common among benthic-feeding species, especially obligate corallivores. Species with broad dietary flexibility tend to have flexible social systems, while plankton feeders are usually gregarious. The widespread occurrence of monogamy in butterflyfishes appears linked to territoriality, the majority of territorial species identified to date occurring predominantly as pairs. Data currently available suggest that this is because pair defence of the territory is more efficient than by individuals. However, several alternative hypotheses for the evolution of monogamy based on spawning constraints and predation risk cannot yet be ruled out.     

A review of protein engineering for the food industry

In this review I briefly describe the technique of protein engineering and indicate how the present state of knowledge allows proteins to be mutated to increase or decrease stability. I discuss experiments on both model proteins and those of relevance to the food industry and show how hydrophobic forces are a major driving force for folding as well as having a major role in thermostability, I also indicate the large contribution that hydrogen bonding, electrostatic interactions and, in a less well predicted way, disulfide bridges make to thermostability.     

Microflora associated with the internal surfaces of rubber and stainless steel milk transfer pipeline

Sterile sections of rubber and stainless steel milk transfer pipeline were inserted sequentially into a milking installation and soiled with fresh raw milk over a period of 5 d. The resultant adherent microbial population was removed and the generic composition of mesophilic and psychotropic types was determined. In all cases Acinetobacter spp. were found to predominate (59.5-75.6%). The generic composition of the raw milk used to soil the milking unit (with inserted pipe section) was determined once during each 5-d soiling period. In general the milk was found to contain a mixed flora in which Gram-positive organisms predominated.     

Microflora associated with the internal surfaces of rubber and stainless steel milk transfer pipeline

Sterile sections of rubber and stainless steel milk transfer pipeline were inserted sequentially into a milking installation and soiled with fresh raw milk over a period of 5 d. The resultant adherent microbial population was removed and the generic composition of mesophilic and psychrotrophic types was determined. In all cases Acinetobacter spp. were found to predominate (59.5–75.6%). The generic composition of the raw milk used to soil the milking unit (with inserted pipe section) was determined once during each 5-d soiling period. In general the milk was found to contain a mixed flora in which Gram-positive organisms predominated.     

A review ofPseudo-nitzschia,with special reference to the Skagerrak,North Atlantic,and adjacent waters

ThePseudo-nitzschia flora of the Skagerrak, North Atlantic, and adjacent waters, comprisingP. pungens, P. multiseries, P. seriata, P. fraudulenta, P. heimii, P. delicatissima, andP. pseudodelicatissima, has been examined. Except forP. australis, allPseudo-nitzschia species shown to produce the toxin domoic acid are present in the area although an outbreak of amnesic shellfish poisoning has never been reported. For comparison of morphological and taxonomic characters,Pseudo-nitzschia seriata f.obtusa, P. australis, P. subfraudulenta, P. subpacifica, P. lineola, P. inflatula, andP. cuspidata have been included in this investigation. Fine details of band structure and poroid occlusions, previously ignored or unresolved, have proven to add to the morphological distinction betweenP. pungens andP. multiseries, P. seriata andP. fraudulenta, P. seriata andP. australis, andP. delicatissima andP. pseudodelicatissima. Additional information on the structure of the proximal mantle compared to that of the valve face has revealed similarities in most of the species but differences betweenP. pungens andP. multiseries. The species seasonal and long-term distributional patterns during the sampling period (October 1978 through September 1993) in the Skagerrak area are outlined. The greatest abundances ofP. seriata, a cold-water species most likely restricted to the northern hemisphere, occurred in the spring, and those of the presumably cosmopolitan diatomsP. pungens, P. multiseries andP. pseudodelicatissima, in the autumn. WhereasP. multiseries seems to have decreased in abundance in the 1990s,P. pseudodelicatissima has apparently increased.