Quorum Sensing Inhibitory and Antibiofilm Activities of Actinobacterial Extracts against Chromobacterium violaceum and Pathogenic Bacteria

Antibiotic resistance in microorganisms is a serious public health problem worldwide, highlighting the need for alternative strategies to control bacterial infections. One promising target is quorum sensing (QS), which is a bacterial cell-to-cell communication system that regulates various physiological processes including the production of virulence factors and biofilm formation, both of which contribute to bacterial persistence and resistance. This study investigated the QS inhibitory (QSI) and antibiofilm activities of actinobacteria. A total of 98 actinobacterial isolates were screened for QSI activity using Chromobacterium violaceum KCTC 2897 as the reporter strain. Seven isolates inhibited violacein production without affecting bacterial growth, indicating their potential QSI activity. The crude ethyl acetate extracts from six of these isolates retained their QSI activity. Among these, extract 43N8 exhibited the strongest antibiofilm activity at a sub-minimum inhibitory concentration of 6.25 mg mL-1, reducing biofilm formation by 58.2% in Pseudomonas aeruginosa and 79.7% in Staphylococcus aureus. Extract 42N3 showed the second-highest antibiofilm activity, inhibiting biofilm formation by S. aureus by 62.8%. Phylogenetic analysis using 16S rRNA gene sequences revealed that isolates 43N8 and 42N3 were members of the genus Streptomyces and shared the highest sequence similarity with Streptomyces misionensis NBRC 13063T (99.57%) and Streptomyces barringtoniae LMG 32415T (98.03%). These findings revealed the QSI and antibiofilm potential of actinobacterial extracts, highlighting their potential as sources of bioactive compounds for the development of novel approaches to control bacterial infections.