Antimicrobial Effect of Plasma-Treated Liquids on Skin and Oral Biofilms: A Systematic Review of In Vitro Studies

This systematic review aimed to evaluate the effectiveness of indirect cold atmospheric
plasma (CAP) in disrupting oral and skin microbial biofilms and to investigate whether
the reported effects are mainly attributable to acidic pH, plasma-activated liquids, or
specific devices and treatment settings. The review followed PRISMA guidelines and
was registered on the Open Science Framework. A comprehensive literature search was
conducted across major electronic databases. Studies evaluating indirect CAP on in vitro
oral and skin microbial biofilms were included. Comparisons were made with untreated
controls, non-activated liquids, and conventional antimicrobials. Outcomes were evaluated
based on reductions in biofilm viability or biomass using quantitative assays (e.g., CFU, XTT,
and Crystal Violet). Thirteen in vitro studies were included. CFU-based outcomes were
reported in 11 of 13 studies (84.61%), and all of these studies showed reductions exceeding
5–6 log under specific conditions. Antimicrobial efficacy varied according to exposure time,
microbial species, plasma parameters, and treatment settings, while physicochemical analyses
indicated that acidic conditions and plasma-activated liquids play a key role. Indirect CAP
appears to be a promising non-invasive antimicrobial strategy for managing oral and skin
biofilms. However, variability among devices and settings, together with the absence of
clinical data, underscores the need for further standardized studies and clinical investigations.