Suspension tests, disinfectant

In summary, therefore, the KS suspension test differs from the RW and CM tests in that it is a capacity test, it reports the data as a pass or fail and not as a numerical cipher, i.e. not as a coefficient, and it uses a range of microorganisms. It combines an individual feature ofthe RW and CM tests in that it can report on disinfectant activity under both clean and dirty conditions. 

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. 

Compared with suspended (planktonic) cells, bacteria on surfaces as biofilms are invariably phe-notypically more resistant to antimicrobial agents. With biofilms, suspension tests can be modified to involve biofilms produced on small pieces of an appropriate glass or metal substrate, or on the bottom of microtitre tray wells. After being immersed in, or exposed to the disinfectant solution for the appropriate time interval, the cells from the biofilm are removed, e.g. by sonication, and resuspended in a suitable neutralizing medium. Viable counts are then performed on the resulting planktonic cells. 

The vimcidal activity of monopercitric acid (MPCA) was determined by suspension tests against both nonenveloped and enveloped viruses including VACV [120], The study showed that vimses were 99.9% inactivated by a 0.5% concentration within 30 s demonstrating MPCA as a suitable candidate for a disinfectant. Sugimoto and Toyoshima [107] reported on the inactivation of VACV by N -Cocoyl-L-Arginine Ethyl Ester, DL-Pyroglutamic Acid Salt after a 30 min exposure at room temperature. At all tested concentrations (0.025%, 0.05%, 0.1%, and 0.25%), there was greater than 90% inactivation of VACV. 

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. 

CEN Virucidal Suspension Test for Chemical Disinfectants and Antiseptics Used in Human Medicine DRAFT A suspension of the test virus, with or without a soil load, is mixed with the test agent and the mixture held at 20°C for the desired contact time. The mixture is then titrated for infectious virus. Under review by CEN/TC 216... 

EN 1276 1997, Chemical Disinfectant and Antiseptics-Quantitative Suspension Test for Evaluation of Bactericidal Activity of Chemical Disinfectants and Antiseptics Used in Food, Industrial, Domestic, and Institutional Areas-Test Methods and Requirements, Comite European de Normalization, La Plaine Saint-Denis Cedex France, 1997. 

EN 1276. Chemical disinfectants and antiseptics - Quantitative suspension test for the evaluation of bactericidal activity of chemical disinfectants and antiseptics used in food, industrial, domestic, and institutional areas - Test method and requirements (phase 2/stepl). Brussels European Committee for Standardization. 

Level 1 concerns basic suspension tests, performed with disinfectant dilutions to show if the product is disinfectant or not, and at what concentration. The target is to achieve a 5 log reduction for bacteria and a 4 log reduction for yeast and molds within 1 h (see Table 1). 

Level 3 refers to practical use tests. They are performed in suspension, on specific nonliving surfaces, or on skin, and they allow characterization of effectiveness of a disinfectant product for a particular claimed use. For each of the above three categories, these tests m e use of the same sfiains as the suspension tests. 

In the procedure for the surface test (313), the vims is grown in a monolayer of baby hamster kidney cells and incubated in Eagles medium supplemented with tryptose phosphate broth and calf semm. After separation of the vims from the cells by sonification and centrifugation, amounts of the suspension containing 3 x 10 plaque-forrning units are dried on coversHps. The inoculated coversHps are placed in 5 ml of the disinfectant for 1, 5, or 10 min, then rinsed, sonicated, and assayed. 

A standardized viral suspension is exposed, in the presence of yeast suspension, to appropriate dilutions of disinfectant in WHO hard water. At appropriate times, dilutions are made in inactivated horse serum and each dilution is inoculated into tissue cell culture or embryonated eggs (as appropriate for the test virus). The drop in infectivity of the treated virus is compared with that of the control (untreated) virus. 

Disinfectant and sanitary powders are the subjeet of a British Standard (BS 1013 1946), now withdrawn, whieh describes a method of determining the RW coeffieient of such powders. A weighed quantity was shaken with distilled water at 18°C for 30 minutes and this suspension was used in the test already deseribed (seetion 3.1.1). 

Stainless steel disks are contaminated with a bacterial test suspension and dried. The disinfectant is applied on the dried film on the disk and kept at a specified temperature for a defined time. The disk is than transferred to a previously validated neutralization medium to stop the action of the disinfectant. The cfii of surviving bacteria recovered from the surface is determined quantitatively. 

By electrolysing carbonate and bicarbonate solutions in the ppm range, (Borutzky et al. 2006) no (using MIO anodes) and negligible (using BDD anode) disinfection activity was measured after adding the electrolysed solution to suspensions of microorganisms. Electrolysis samples analysed by DPD test showed low radical formation ( Wursters Red ) so that a small amount of radical formation is likely. 

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