Quorum sensing (QS) is a regulatory mechanism that enables bacteria to make collective decisions such as an increase in virulence factors and biofilm production. Inhibitors of QS are important research tools in the discovery of new potential anti-bacterial agents. Polygodial, drimenol and drimendiol are drimane sesquiterpenoids isolated from Drimys winteri, a Chilean native tree. Their QS activity, when tested on Chromobacterium violaceum ATCC 12472, showed that drimendiol is an inhibitor of QS, decreasing violaceine production in C. violaceum and decreasing biofilm formation of Pseudomonas syringae strains. Consequently it increased the biocide effects of CuSO 4 on biofilms of P. syringae.

Fifteen native Chilean plants were evaluated against the quorum sensing (QS) biosensor AI-1, Chromobacterium violaceum ATCC 12472. Three extracts showed inhibitory activity of QS: Drymis winteri J.R, Psoralea glandulosa L and Peumus boldus. Purification of secondary metabolites from barks of Drimys winteri showed that drimane sesquiterpenes were the main compounds in the tree. Polygodial, drimenol, isodrimeninol, drimenin, isodrimenin, cinnamolide and valdiviolide were isolated and evaluated in QS inhibition assays. Two α,β unsaturated lactones, cinnamolide and valdiviolide, with the carbonyl on position 12 of the drimane skeleton were found to be inhibitors of QS; other drimane lactones were not active.

The appreciation of biofilm structures in digital images can be subjective to the observer, and hence it is necessary to analyse the underlying images in useful parameters by means of quantification that is, ideally, free of errors. This paper proposes a combination of techniques for segmentation of biofilm images through an optimal multi-level thresholding algorithm and a set of clustering validity indices, including the determination of the best number of thresholds. The results, which are validated through Rand Index and a quantification process performed in a laboratory, are similar to the quantification and segmentation done by an expert.

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