ASTM E3031–20. Standard Practice for Determination of Antibacterial Activity on Ceramic surfaces.
Test accredited by ENAC (Spanish National Accreditation Entity).
ASTM E3031 describes a method for the quantitative evaluation of the antibacterial activity of glazed ceramic surfaces that have been specifically designed to contain an antibacterial treatment. This method aims to solve some limitations of the methods described by the ASTM E2180 and ISO 22196 standards, which do not take into account the complexities associated with a ceramic surface. For this, the ASTM E3031 standard incorporates an initial step of prehydration of the ceramic pieces to avoid the drying of the surface by absorption of water through the body of the piece and admits the use of borosilicate glass control pieces, when there are not available pieces equal to those of the test but whose enamel is free of antibacterial components, or if the chemicals in the enamel make these pieces not support the growth of microorganisms under the test conditions, and therefore are not suitable for the comparison.
The test procedure begins with the prehydration of the ceramic samples, placing the pieces on moistened wipes and incubating them at 35ºC ± 2ºC at > 75% relative humidity for 18 to 24 hours. After this period, the glazed ceramic pieces with antibacterial properties and the control pieces (pieces whose enamel does not contain elements with antibacterial properties, or pieces of borosilicate glass) are inoculated with a suspension of Escherichia coli of known concentration, and incubated 24 hours at 35ºC ± 2ºC. Subsequently, the bacteria are recovered in a neutralizing broth and counted by plating. The comparison of the logarithmic reductions obtained from the ceramic samples with antibacterials and the control ceramic samples without antibacterials, allows to determine if the antibacterial treatment incorporated in the enamel is considered bacteriostatic, bactericidal, if it produces a partial inhibition or if it does not have effect on bacterial growth.
Square pieces of 50 mm ± 1 mm are used in the test. In total, 5 pieces are required with the enamel containing the antibacterial element and 5 similar pieces with the enamel without antibacterial elements. If it is not possible to have untreated pieces available, or if due to their chemical composition these are not adequate to support bacterial growth, the manufacturer can justify it and supply 10 pieces of borosilicate glass of the same size. However, if it is necessary to repeat any part of the test or confirm a result, it is recommended to send twice the number indicated, that is, 20 pieces (10 with antibacterial enamel and 10 with enamel without antibacterial properties or borosilicate glass).