Emerald Group Publishing Limited
Copyright © 2000, MCB UP Limited
An in-use study of Microban ® cleaning cloths
An in-use study of Microban ® cleaning cloths
A recent survey of 1,773 people in the UK by Health Which? suggested that over half the people in the UK have bought an antibacterial product of some kind. These range from cleaning chemicals to the various household products which have anti-microbial properties (Anon, 1999). Microban ® is an example of one of these materials which can be manufactured into a range of household products. It incorporates Triclosan as its active ingredient, a compound which has been used for many years in a variety of products which include deodorants, mouthwashes, soaps and toothpastes (Sainsbury's, 1997a).
Microban ® products have been exclusively available in the Sainsbury's chain of supermarkets since October 1998 and have been used in their stores for a range of fittings and staff clothing in addition to products available to the consumer which range from cutting boards to toilet brushes. Advertising surrounding these products is designed to lead us to believe that they "offer in-built protection against harmful bacteria in our kitchen" but only if "we stick to our normal hygiene regimes" (Sainsbury's, 1997a). What is normal may not necessarily be hygienic as has been demonstrated by a number of researchers (Worsfold and Griffith, 1997; Food and Drink Federation (FDF), 1993, 1994, 1995, 1996) and the extent to which the consumer may be misled by the marketing of this product is a subject for debate and further investigation.
In April 1997 the US Environmental Protection Agency ( EPA) arrived at an enforcement agreement which prevented a toy manufacturer from making public health claims that their toys made from materials incorporating Microban ® "protect children from germs and disease-causing bacteria such as E. coli and Salmonella" (EPA, 1997). The background for this enforcement agreement had its origins in the registration of the Microban ® pesticide and the subsequent claims made by the manufacturer in its promotional materials. The plastic material which has a Microban ® treatment was registered by the EPA to inhibit bacterial growth in plastic; however, the Federal Insecticide, Fungicide and Rodenticide Act states that public health claims for products treated with pesticides cannot be made unless the product itself has been approved or registered by the EPA. Despite the fact that Microban ® itself was registered with the EPA, toys containing Microban ® had not been registered for public health use. The registration was limited to protecting objects from the growth of bacteria which cause products to smell or deteriorate (EPA, 1997).
The manufacturers of Microban ® responded but their motion to dismiss was denied in April 1998. It was not denied that the product was ineffective against Salmonella, Escherichia coli or Staphylococcus aureus, but claims were being made which were different from those made as part of its registration.
In the UK Sainsbury's promotional material emphasises that these products are not a substitute for good hygienic practice and that they should be used in conjunction with effective cleaning regimes (Sainsbury's, 1999). What has not been addressed, however, is public understanding and expectations of these products. Will consumers use them as a substitute for, or an adjunct to, good hygienic practice? A recent survey by Health Which? magazine suggested that 57 per cent (1,011) of the people interviewed thought that "these products would make people complacent" and 17 per cent (164) of people who had bought anti-microbial products were of the opinion that these products would require less cleaning (Anon, 1999).
The main active ingredient Triclosan in Microban ® products is a hydrophobic and trichlorinated phenol. It is incorporated during the manufacturing stage in sufficient quantities to provide protection for the lifetime of that product. The Triclosan molecules are able to migrate within the product and some migrate to the surface where they become effective against a range of bacteria (Hanrahan and Patil,1996). In use, Triclosan works by damaging the cytoplasmic membrane of the micro-organisms that it comes into contact with, which results in the leakage of cellular material and prevents the uptake of amino acids and hence further cell growth (Levy et al., 1999; McMurry et al., 1998). The process of cleaning removes Triclosan molecules from the surface; this disrupts the balance in the matrix and consequently more molecules migrate to the surface and come into contact with micro-organisms. Various uses of Microban ® have been tested and have shown to be 90 per cent effective against a range of organisms such as Staphylococcus aureus, Escherichia coli and Klebsiella pneumoniae (Medlin, 1997).
The aim of this present study was to compare the effectiveness of Microban ® products with that of conventional materials in reducing bacterial contamination of cleaning cloths.
Materials and methods
Preparation of soilA standard food soil using the following recipe was prepared, by blending the ingredients in a food processor. The result simulated the soil commonly encountered on dirty plates (BS 6584, 1985):
one tin of Tyne Brand tinned mince (400g);
one tin of Ambrosia Devon Custard (400g);
one tin of Heinz Tomato Soup (400g);
5g of Sainsbury's Gravy Granules;
150g of Sainsbury's Instant Potato;
50ml of corn oil;
100ml of lard;
300ml of water;
two eggs (medium).
The soil was then divided into 90ml quantities, placed in sterile beakers and frozen. Prior to use, a 90ml quantity of soil was defrosted and inoculated with 10ml of an overnight culture at 37°C of E. coli NCTC 6099 in nutrient broth (Oxoid CM). Prior analysis showed that the viable count of such cultures was approximately 10 8 cfu/ml.
Preparation of dinner platesThe inoculated soil was well mixed and then 5ml inoculated on to each of five sterile 20cm dinner plates and spread using a sterile brush. The plates were then allowed to stand at room temperature for 30 mins.
Preparation of the washing waterAn amount of 5ml of Sainsbury's Concentrated Washing-Up liquid was added to a clean plastic washing up bowl containing 5l of sterile de-ionised water which had been pre-heated to 48°C.
Washing the platesThe five plates were then washed using a Sainsbury's all purpose cloth, seven times in a circular motion on the face, twice on the back and once more on the face. The cloth was then placed in a sterile plastic bag.
AnalysisAn amount of 200mls of Maximum Recovery Diluent (Oxoid) was added to the bag which was then placed in a Colworth stomacher for two minutes. Serial dilutions to 10 -4 were prepared from the stomacher liquid.
An amount of 1ml of the sample was then transferred to a sterile petri dish, followed by 20ml of melted Cystine-Lactose-Electrolyte-Deficient (CLED) medium (Oxoid CM) at 50°C. The plates were mixed, allowed to set and then incubated at 37°C for 24 hours.
The procedure was then repeated from step 2 for three more cloths which were then incubated at 25°C for three, six and 24 hours respectively in order to simulate various in-use conditions of storage.
The experimental procedure was repeated for different combinations of cloths and detergents (treatments) as shown in Table I and replicated five times.
Results and discussion
This investigation evaluated the performance of Microban ® products over a period of 24 hours where they had been used to wash up plates covered with a standard inoculated soil. The results showed that immediately after the washing up procedure there were no significant differences in the degree of contamination of any of the cloths between any of the four treatments. Thereafter, the results showed (see Table II>) that for all treatments the numbers of E. coli increased over 24 hours; however, the increases in the counts of E. coli for treatment 4 (Sainsbury's Microban ® cloth/Sainsbury's Microban ® washing-up liquid ) were less than for the other combinations, about 14 per cent below the least favourable combination treatment 1. However, none of the observed differences at t = 24 was significant (F = 0.83, p = 0.52).
The degree of contamination of these cloths was entirely consistent with the work of a number of researchers who demonstrated that cleaning cloths are commonly contaminated with between 10 3 and 10 6 organisms/cm 2 (Davis et al., 1968; Mendes et al., 1978; Scott et al., 1982). These levels are unacceptable in the domestic kitchen where there may be the potential for cross-contamination of high risk food (Scott and Bloomfield, 1989).
These results demonstrate, as Sainsbury's so rightly said, that Microban ® is not a panacea for all ills (Sainsbury's, 1997b). It could also be argued that, while Microban ® has the ability to reduce numbers of E. coli over time, the magnitude of this reduction contributes little to improvements in hygiene. This is particularly significant where some pathogenic bacteria such as verocytotoxin producing E. coli 0157 have infective doses as low as 100 but may occur in millions on contaminated cloths (PHLS, 1998g).
It is also worth considering the background to this concern. Food poisoning figures continue to rise despite increased regulation of the food industry, supporting the view that many sporadic cases have their origin in the home. Recent figures show that between 1992 and 1997 for Salmonella species 17 per cent of general outbreaks occurred in the home (PHLS, 1998a, 1998b, 1998c, 1998d, 1998e). Similar figures for E. coli 0157 show that 11 per cent of general outbreaks occurred in the home (PHLS, 1998f). It may be the case that as a nation we are losing our ability to handle raw food safely and maintain basic hygienic standards in the home. This view is supported by the results of the numerous surveys undertaken on behalf of the Food and Drink Federation since 1993 (FDF, 1993, 1994, 1995, 1996).
Public understanding of the protection Microban ® affords and the intended use of these products is unclear. Sainsbury's maintain that 70 per cent of customers questioned said they were likely to buy such products for use in their homes (Sainsbury's, 1997b). There is a concern that if the public believes that the product has a self-sanitising property then they may not implement basic hygiene measures which are necessary to prevent cross-contamination (EPA, 1997). Whether or not these same 70 per cent fully understand the nature of these products and the necessity to maintain rigorous hygiene standards is open to question. The American experience and the recent survey conducted by Health Which? highlight the concerns and the need for further research in this area.
Lucy MeredithBath Spa University College, Bath, UK
Roger John LewisUniversity of the West of England, Bristol, UK
Mary HaslumUniversity of the West of England, Bristol, UK
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