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Ireland were screened for the production of antimicrobials and quorum sensing inhibitors. (QSIs). 37 bacterial isolates were found to inhibit QS-dependent pigment production in Chromobacterium violaceum ATCC12472 or Serratia sp ATCC39006. The organic extracts of five isolates caused a significant decrease in both total biomass and biofilm viable counts displaying a range of growth inhibitory and antimicrobial activities. All five organic extracts caused a reduction in Pyocyanin production while three extracts significantly decreased the production of Pyoverdin in P. aeruginosa PAOI. The ability of the algae Bonnemaisonia hamifera and Halidrys siliquosa to produce antibiofilm bioactives was also investigated. Algal extracts of B. hamifera had varying degrees of antibiofilm activity on P. aeruginosa PAOl, E. coli ATCCl1303 and P. mirabilis ATCC7002. The antibiofilm activity of the chloroform, acetonitrile, and hexane extracts was found to be consistent with the presence of QSls detected using both, QSI reporter strain C. violaceum A TCC 12472 and with the luminescence-based bioreporter strains E. coli JMI09 pSB 1142 and JM 109 pSB536 suggesting a QSI -dependent mechanism. The methanolic extract of the alga H. siliquosa failed to display any QSI activity but was found to possess a broad-spectrum antimicrobial activity against bacteria belonging to the genus Staphylococcus, Streptococcus, Enterococcus and Propionibacterium with MBEC values of 1.25 mg/ml for both S. aureus (MRSA) 33593 and P. acnes lA. Bioassay-guided fractionation of the extract allowed the isolation of three compounds displaying antimicrobial and antibiofilm activity against MRS A ATCC33593. The molecular weights of the compounds was determined by UPLCqTOF- MS (442, 442 and 428 m/z respectively) and found to differ from the meroditerpenoids previously extracted from this alga {{902 Culioli,G. 2008;}}. The MBEC values of MRSA ATCC33593 were 0.028mg/ml (64/lM) for compounds 1 & 2 and 0.055 mg/ml (128 /uM) for compound 3. Structural elucidation of the three antimicrobials is currently underway in collaboration with Prof. Tasdemir, NUIG, Galway. |
