Assessing non-porous antimicrobial surfaces against bacteria, phages and fungi: a comparative study under varied normative conditions using glass as a benchmark for microbial persistence

The survival of pathogenic microorganisms on surfaces is contingent on environmental factors, including humidity and temperature. In order to analyze the survival and persistence in vitro, different protocols have already been implemented. This has resulted in a wide range of survival rates of all kinds of microorganisms on various surfaces tested, due to different procedures across laboratories. This study aims to provide a comprehensive overview of the antimicrobial performance of glass, as an inert reference material, and low alloyed carbon steel with different antimicrobial additives. Therefore, three complementary testing strategies that simulate both dry and moist environmental conditions were utilized: the standardized ISO 22196:2011 for humid exposure, a spray-chamber method mimicking aerosol-based contamination with dry test conditions, and a biofilm formation assay under air/liquid interface conditions. A range of microorganisms, including Gram-positive and Gram-negative bacteria, fungi, and bacteriophages demonstrated long-term persistence on glass, ranging from at least two days to weeks. In the liquid test, low alloyed carbon steel uncoated and coated with zinc or an antimicrobial lacquer achieved good efficacy against bacteria and bacteriophages. However, in the dry tests and in tests against fungi, only the antimicrobial lacquer was effective. Furthermore, none of the tested surfaces prevented biofilm formation by Pseudomonas aeruginosa. Thus, the study demonstrated that different test scenarios yield disparate outcomes, emphasizing the importance of in vitro testing being oriented towards the intended product applications. It also demonstrated the requirement of suitable reference materials like glass to benchmark microorganism persistence under specific testing scenarios.