Comparative examination of in vitro methods to evaluate the antimicrobial activity of biomaterials

One of the basic building blocks of biomaterials is antimicrobial activity. It is an unacceptable misconception that this property cannot be determined due to incorrect methods and faulty microorganism selection. This study covers the determination of the most appropriate microbial activity test according to the type (metal, polymer, ceramic coating) and chemical form (liquid, solid) of the biomaterial by comparing methods. In our study, there are four biomaterial groups: Metal (titanium, zinc, iron), metal alloy (Ti6al4V, iron manganese), Polymer polymethylmethacrylate, polycaprolactone, polylactic acid and polyhydroxy butyrate), Composite polymer (polyhydroxybutyrate-valerate), Ceramic and Additives (hydroxyapatite, titanium dioxide, zinc oxide) and Composite material (zinc titanium oxide) with diferent amounts of Zinc). Microorganisms in the experimental studies included gram-positive bacteria (Bacillus subtilis, Staphylococcus aureus, Enterococcus faecalis, Staphylococcus epidermidis), gram-negative bacteria (Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Salmonella typhi and a fungus (Candida albicans). Antimicrobial assays are performed by 1-Difusion methods (Agar disk difusion method), 2- Antimicrobial gradient method (Etest), 3- Serial dilution, 4-Time kill test (time kill curve) and 5- Colony counting method. The possible antimicrobial activities of PHB, C-PLA and PHB-V polymers and the superior antimicrobial activity results of zinc and metal-based composite biomaterials were clearly determined by utilizing the correlations of multiple test methods. Colony counting and time-kill tests were linearly correlated with other test methods, mainly depending on the solubility of the biomaterials. If researchers know the structural characteristics of the biomaterial they have, this study explains which microorganisms and which test methods will lead to the correct result. The most different and most necessary motivator in our study is the need to recognize that the compatibility between the antimicrobial activity studies of biomaterials is as perfect and single-solution oriented as the key-lock compatibility. A simple template for basic antimicrobial activity testing methods for metal, ceramic, polymer and composite biomaterials.