Beyond lethal doses: sub-MIC levels of multi-class antibiotics induce species- and isolate-dependent biofilm inhibition in gram-negative pathogens

Background

Biofilm-associated infections remain a major clinical challenge due to their intrinsic tolerance to antimicrobial therapy. Sub-minimum inhibitory concentrations (sub-MICs) of antibiotics are frequently encountered in vivo, particularly at sites of infection and on indwelling medical devices. However, their influence on biofilm formation is controversial, with evidence of both stimulatory and inhibitory effects. Clarifying these responses may reveal novel therapeutic opportunities for managing nosocomial biofilm-related infections. This study aims to investigate the effects of three sub-MIC concentrations (25%, 50%, and 75% of MIC) of five antibiotic classes on biofilm formation in Pseudomonas aeruginosa, Escherichia coli, and Klebsiella pneumoniae using two distinct biofilm quantification methods.