Disinfection efficacy testing

Unfortunately, standardization of the methodology to be employed in these efficacy tests has proved difficult, if not impossible, to obtain, as has consensus on what level of killing represents a satisfactory and/or acceptable result. It must be stressed however, that unlike tests involving chemotherapeutic agents where the major aim is to establish antimicrobial concentrations that inhibit growth (i.e. MICs), disinfectant tests require determinations of appropriate cidal levels. 

SVW Sutton. Neutralizer evaluations as control experiments for antimicrobial efficacy tests. In JM Ascenzi, ed. Handbook of Disinfectants and Antiseptics. New York Marcel Dekker, 1996, pp. 43-62. 

Wirtanen, G. and S. Salo. 2003. Disinfection in food processing-efficacy testing of disinfectants. Rev. Environ. Sci. Biotechnol. 2 293-306. 

The efficacy tests used are the MIC test and other tests based on the same principle as the disinfectant tests (see Sec. II. B). The bacteria used in the tests are chosen among strains representative of those found in the home for example, bacteria from the Pseudomonas family, the Enterobacteriaceae, yeast such as Candida, molds such as Aspergillus niger, and others. 

The principle of tests evaluating the efficacy of surgical hand disinfectants is to sample the resident flora of the hands before and after surgical hand disinfection. 

For assaying herpes virus, monolayers of baby hamster kidney (BHK) cells are used. Virus titre is expressed as the number of plaque-forming units (pfu) per millilitre before and after exposure to a disinfectant, so that the virucidal efficacy of the test agent can be determined. A diagrammatic representation is given in Fig. 11.7. 

Method for assessing the efficacy of disinfectants by the modified ChickMartin test BS 808 1986 [1991]. 

The reason for this confusing situation is that all efficacy data are depending from the test method used to find the effective time - concentration ratio of the disinfectant. 

The first mechanical variant uses a presoaked cotton swab on the surface covered with the disinfectant solution, the second variant uses a presoaked swab without disinfectant on the test surface. Both methods have been tested by Prof. Koller in Vienna and the first variant showed a higher efficacy than the second (using more disinfectant on the surface). 

Experiments with gaseous acetic acid have been performed for disinfection of seeds intended for the production of bean sprouts (Delaquis et al., 1999). Salmonella typhimurium and E. coli 0157 H7 were eradicated from the surface of mung bean seeds and it was reported that the seed germination loss was not too large. The seeds have often been the suspected source of contamination in sprout-associated outbreaks and sanitation methods that do not interfere with the germination of the seeds are appreciated. Other volatile chemical treatments have been tested for lethality to Salmonella spp. on alfalfa seeds and sprouts with varying results both on the efficacy of the disinfectant and its effect on sensory qualities (Weissinger et al., 2001). 

Tests were carried out to demonstrate the efficacy of the inventive composition in disinfecting drinking water. 

Chick s early work at the Lister, undertaken with Charles Martin,37 was on the chemical kinetics of the disinfection process. Of particular importance, she found that the temperature dependence of the disinfectant action did not follow the Arrhenius rate expression instead, the rate increased by as much as seven- or eight-fold for a 10°C increase in temperature, thus showing that warm disinfectant solutions were far better for killing bacteria than cold solutions. This led to her being the co-developer of the Chick-Martin Test for the efficacy of a disinfectant. 

Alternative treatments reported for chronic endometritis include intrauterine infusion of a variety of disinfectants, irritants, autologous or heterologous blood plasma, colostrums and filtrates of bacterial toxins as well as systemic treatment with immunostimulants. These treatments are controversial since their clinical efficacy and safety have not been tested in controlled studies. It is possible that they may cause... 

Phenol coefficient tests were developed in the early 20th century when typhoid fever was a significant public health problem and phenolics were used to disinfect contaminated utensils and other inanimate objects. Details of such tests can be found in earlier editions of this book. However, as non-phenolic disinfectants became more widely available, tests that more closely paralleled the conditions under which disinfectants were being used (e.g. blood spills) and which included a more diverse range of microbial types (e.g. viruses, bacteria, fungi, protozoa) were developed. Evaluation of a disinfectant s efficacy was based on its ability to kill microbes, i.e. its cidal activity, under environmental conditions mimicking as closely as possible real life situations. As an essential component of each test was a final viability assay, removal or neutralization of any residual disinfectant became a significant consideration. 

Simulated use tests involve deliberate contamination of instruments, inanimate surfaces, or even skin surfaces, with a microbial suspension. This may either be under clean conditions or may utilize a diluent containing organic (e.g. albumin) material—dirty condition. After being left to dry, the contaminated surface is exposed to the test disinfectant for an appropriate time interval. The microbes are then removed (e.g. by rubbing with a sterile swab), resuspended in suitable neutralizing medium, and assessed for viability as for suspension tests. New products are often compared with a known comparator compound (e.g. 1 minute application of 60% v/v 2-propanol for hand disinfection products— see EN1500) to show increased efficacy of the novel product. 

These tests are used to test a new raw material or a complete formula. They are also used to support claim substantiation. They are easy, safe, and cheap tests and are designed to simulate actual use conditions. The first three of the tests discussed below can be used to screen products for either handwash products or for efficacy as surface disinfectants, as they test for bacteriocidal or bacteriostatic action without reference to a surface. The last two tests are specifically used to document surface disinfection claims. 

Gaustad, J.W., McDuff, C.R., and Hatcher, H.J., 1974. Test method for the evaluation of virucidal efficacy of three common liquid surface disinfectants on a simulated environmental surface. Appl. Microbiol., 28 748-752. 

D Michel, GA Zach. Antiseptic efficacy of disinfecting solutions in suspension test in vitro against methiciUin-resistant Staphylococcus aureus. Pseudomonas aeruginosa and Escherichia coli in pressure sore wounds after spinal cord injury. Dermatology 195 (suppl 12) 36-41, 1997. 

British Standard 808, Method for Assessing the Efficacy of Disinfectants by the modified Chick-Martin test, 1986. 

---