The antimicrobial substance's content influences the membrane blocking mechanism in cross-flow filtration – Flow cytometric assessment of the membrane's activity

The study aims to investigate the antibacterial properties of carvacrol-loaded cellulose acetate membranes in cross-flow filtration using an advanced microbiological flow cytometry method and analyze the influence of carvacrol's presence on the pore-blocking mechanisms. The commercial cellulose acetate microfiltration membranes were impregnated with carvacrol using supercritical carbon dioxide as a solvent and transport medium. This technique enables active substance distribution throughout the whole polymer volume on the molecular level. Carvacrol loadings of up to 30 % were obtainable, whereby the membranes preserved their microstructure and functionality for loadings of up to 25 %. The protocol for flow cytometric assessment of the cell deposition on the membrane surface during the cross-flow filtration was developed. The results showed that the presence of carvacrol considerably decreased Staphylococcus aureus deposition on the membrane (from the order of magnitude 107/(cm2membrane surface·mLpermeate) to 105/(cm2membrane surface·mLpermeate)). The membranes containing 20 % and 25 % carvacrol showed the largest permeate flux and the smallest number of deposited bacteria. The largest fraction of dead bacteria (42 %) was detected in the membrane containing 25 % carvacrol. Mathematical modeling showed that the pore-blocking mechanism changed with the increase in carvacrol content, from the cake filtration phenomenon via the intermediate blocking towards standard and complete blocking mechanisms.