Antibiofilm activity from endophyte bacteria, Vibrio cholerae strains, and actinomycetes isolates in liquid and solid culture

BACKGROUND: Biofilm-associated infections are a global threat to our economy and human health; as such, development of antibiofilm compounds is an urgent need. Our previous study identified eleven environmental isolates of endophyte bacteria, actinomycetes, and two strains of Vibrio cholerae as having strong antibiofilm activity, but only tested crude extracts from liquid culture. Here we grew the same bacteria in solid culture to induce the formation of colony biofilms and the expression of genes that may ultimately produce antibiofilm compounds. This research aimed to compare antibiofilm inhibition and destruction activities between liquid and solid cultures of these eleven environmental isolates against the biofilms of representative pathogenic bacteria. RESULTS: We measured antibiofilm activity using the static antibiofilm assay and crystal violet staining. The majority of our isolates exhibited higher inhibitory antibiofilm activity in liquid media, including all endophyte bacteria, V. cholerae V15a, and actinomycetes strains (CW01, SW03, CW17). However, for V. cholerae strain B32 and two actinomycetes bacteria (TB12 and SW12), the solid crude extracts showed higher inhibitory activity. Regarding destructive antibiofilm activity, many endophyte isolates and V. cholerae strains showed no significant difference between culture methods; the exceptions were endophyte bacteria isolate JerF4 and V. cholerae B32. The liquid extract of isolate JerF4 showed higher destructive activity relative to the corresponding solid culture extract, while for V. cholerae strain B32 the solid extract showed higher activity against some biofilms of pathogenic bacteria. CONCLUSIONS: Culture conditions, namely solid or liquid culture, can influence the activity of culture extracts against biofilms of pathogenic bacteria. We compared the antibiofilm activity and presented the data that majority of isolates showed a higher antibiofilm activity in liquid culture. Interestingly, solid extracts from three isolates (B32, TB12, and SW12) have a better inhibition or/and destruction antibiofilm activity compared to their liquid culture. Further research is needed to characterize the activities of specific metabolites in solid and liquid culture extracts and to determine the mechanisms of their antibiofilm actions.