Quantitative surface test for the evaluation of residual antimicrobial (bactericidal and/or yeasticidal) efficacy of liquid chemical disinfectancts on hard non-porous surfaces.

(NF PAS 2424: 2014)

Test not accredited in our laboratory.

Increasingly, numerous biocidal products claim to have residual antimicrobial activity (claiming lasting protection, 24-hour protection or residual action). PAS 2424 specification describes a test method to determine whether or not a product exhibits residual antimicrobial activity on hard non-porous surfaces over a 24-hour period and with abrasive action. This test method is applicable to products used on hard surfaces in the food industry, institutional areas such as schools, hospitals and nursing homes, in the workplace and in the home or domestic environment.

In the test method described by PAS 2424, a prepared sample of the test disinfectant product (pure or diluted) is applied to is applied to steel discs that have previously been inoculated with the mandatory test bacteria (Pseudomonas aeruginosa, Staphylococcus aureus, Enterococcus hirae and Escherichia coli) and/or the mandatory yeast (Candida albicans), and allowed to dry. Over a 24-hour period, the discs undergo a series of abrasion cycles and inoculations designed to simulate the abrasion and re-contamination of a surface to simulate the abrasion and re-contamination of a surface that occurs in between product applications in its real use. For this purpose, three cycles of dry abrasion, re-inoculation and wet abrasion are applied. 24 hours after product application, the discs are exposed to a final inoculum challenge and incubated under defined conditions (at 20°C, with 3.0 g/L of bovine albumin as interfering substance), for a specific contact time (5 min for bacteria and 15 min for yeast). After this contact time the discs are transferred to a neutralizer solution so that the action of the disinfectant is quenched. The number of surviving organisms recovered from the disks is quantitatively determined. The number of bacteria or yeast on a steel disc treated with hard water instead of disinfectant is also determined. For each test microorganism, 5 replicate discs are treated with the test product and 5 replicate discs are treated with hard water. The reduction in viable counts as a result of the residual product is calculated by the difference between the mean of counts obtained from both disc groups. In order to demonstrate residual efficacy, the product shall give a ≥ 3 log reduction when challenged 24 hours after product application. Products shall be tested at their in-use concentration. The customer must indicate the concentration at which his product must be tested, according to its actual conditions of use.

Products that are tested using this method shall also meet the criteria specified by the EN 13697 Standard. PAS 2424 specification is considered an extension of this Standard and it was designed to be used in conjunction with EN 13697. Test results from PAS 2424 will only be considered if the test product also complies with EN 13697 (reduction ≥ 4 log) under the conditions required for the product use application.

For a claim of residual activity using the PAS 2424 test method, the test must be passed under the mandatory conditions: with the microorganisms indicated above, at 20°C, with 3.0 g/L of bovine albumin, and with a contact time 5 min for bacteria and 15 min for yeast.

Where appropriate, for specific purposes, additional bactericidal/yeasticidal activity should be determined under other conditions (time, temperature, interfering substances and number of abrasion cycles) in order to take into account intended specific use conditions. For certain product applications, additional test organisms such as Listeria monocytogenes, Salmonella typhimurium, and methicillin-resistant Staphylococcus aureus (MRSA) can be used. Some examples of additional interfering substances stated by the specification that additional interfering substances may be chosen according to the product´s intended use are: milk, yeast extract, sucrose, SDS and buffers (cleaning).