Evaluation of <i>in vitro</i> Combined Activity of Aqueous Licorice Extract and Fosfomycin Against <i>Escherichia coli</i>

Abstract

Background: The increasing prevalence of antibiotic-resistant Escherichia coli underscores the urgent need for novel strategies to improve antibiotic efficacy. Objectives: This study examined the in vitro potential of an aqueous licorice (Glycyrrhiza glabra) extract in combination with fosfomycin against E. coli. Methods: Antimicrobial interactions were evaluated using the checkerboard method, followed by time-kill and biofilm formation assays. The checkerboard assay demonstrated an interaction between an aqueous licorice extract and fosfomycin, with a fractional inhibitory concentration index (FICI) of 1, which was interpreted as indifferent. Results: Time-kill analysis demonstrated a bactericidal effect over 24 hours at the licorice/fosfomycin FICI concentration, with a significant reduction in viable cell counts compared with licorice alone at its minimum inhibitory concentration (MIC). Furthermore, the combination of licorice and fosfomycin significantly reduced biofilm biomass at different concentrations, indicating potential to prevent biofilm-associated infections. Conclusions: Under in vitro conditions, aqueous licorice extract combined with fosfomycin exhibited antimicrobial activity against E. coli, although the checkerboard interaction was indifferent (FICI = 1). This combination may have potential as an adjunct strategy for managing E. coli infections, particularly those involving biofilm-associated resistance.