Antibacterial Materials: Influence of the Type and Conditions of Biological Tests on the Measured Antibacterial Activity

In recent years, the growing problem of antibiotic resistance has highlighted the need for antibacterial materials to prevent the development of infections. Different types of tests exist to certify the antibacterial properties of materials. Variations in results can occur due to the unique requirements of each test technique. The antibacterial test result may be influenced, in particular, by the distinct modes of action of leaching and non-leaching compounds. Using antibacterial materials prepared by the dispersion of an amphiphilic cationic synthetic copolymer in a polyurethane matrix, the influence of the reaction medium and the contact time on the results obtained by two well-established tests: ISO 22196 and CERTIKA is investigated. This shows that the kinetics of killing is bacteria dependent and depending on the test conditions (concentration of salt, time of contact, or media), contradictory results could be obtained. Moreover, the influence of the ionic strength (called salt effect) in both free solution and antibacterial surface is highlighted.