Abstract
<title>Abstract</title> <p> <italic>Pseudomonas aeruginosa</italic> is an opportunistic pathogen that frequently forms biofilms at infected sites and is known for its ability to tolerate various antimicrobial treatments. <italic>P. aeruginosa</italic> regulates its biofilm development through multiple genetic pathways including quorum sensing (QS) and the intracellular signalling molecule, cyclic diguanylate monophosphate (c-di-GMP). In previous reports, terrein, a secondary metabolite produced by the fungus <italic>Aspergillus terreus</italic> , was previously demonstrated to possess antimicrobial activities against several bacterial species, but against <italic>P. aeruginosa</italic> , it was demonstrated to inhibit biofilm formation and virulence without affecting its viability by interfering with QS and c-di-GMP. However, in this study, we reveal that there is significant strain-to-strain variation of QS and c-di-GMP. Terrein is the first anti-QS compound that demonstrates completely opposite effects of biofilm inhibition/induction across a panel of strains and isolates. In addition, terrein has a stronger effect in the early stage of biofilm development than against mature biofilms. </p>