Antibacterial and antibiofilm activities of supercritical fluid extract and post-extraction waste of Salvia officinalis

Abstract

The increasing prevalence of biofilm-associated infections necessitates the discovery of alternative antivirulence strategies in the management of resistant and chronic infections caused by opportunistic pathogens. In this study, the antibacterial and antibiofilm activities of the extract obtained by supercritical fluid extraction (SFE) of Salvia officinalis and the waste fractions after extraction were investigated in vitro. Antibiofilm activity was determined using the crystal violet method on biofilm-producing strains Acinetobacter baumannii ATCC 19606, Pseudomonas aeruginosa ATCC 15692, and Staphylococcus epidermidis ATCC 35984, while antibacterial activity was assessed as minimum inhibitory concentration (MIC) by the broth microdilution method in accordance with EUCAST standards. The results revealed that all fractions exhibited limited activity against Gram-negative strains (A. baumannii and P. aeruginosa) with an MIC value of 2500 µg/mL, whereas the SO and SOE fractions showed antibacterial effect against the Gram-positive and high-biofilm-capacity S. epidermidis with an MIC of 312.5 µg/mL, and the SOA fraction with an MIC of 625 µg/mL. The most striking antibiofilm activity results were observed with S. epidermidis, where SO achieved 94.3%, SOA 90.1%, and SOE 87.1% inhibition rates, demonstrating very strong effects; in P. aeruginosa, SOA exhibited the highest inhibition at 68.1%; and in A. baumannii, only the SOA and SOE fractions displayed significant inhibition around 68–69%. These findings highlight the potential of S. officinalis SFE extracts—and particularly the extraction waste that are typically discarded—as natural, effective, and sustainable antimicrobial/antibiofilm agents.