Quorum sensing enables bacteria to control the gene expression in response to the cell density. It regulates a variety of bacterial physiological functions such as biofilm formation, bioluminescence, virulence factors and swarming which has been shown contribute to bacterial pathogenesis. The use of quorum sensing inhibitor would be of particular interest in treating bacterial pathogenicity and infections. In this work, we have tested caffeine as quorum sensing inhibitor by using Chromobacterium violaceum CV026 as a biosensor. We verified that caffeine did not degrade the N-acyl homoserine lactones tested. In this work, it is shown that caffeine could inhibit N-acyl homoserine lactone production and swarming of a human opportunistic pathogen, namely Pseudomonas aeruginosa PA01. To the best of our knowledge, this is the first documentation providing evidence on the presence of anti-quorum sensing activity in caffeine. Our work will allow caffeine to be explored as anti-infective drugs.

We report the degradation of quorum sensing N-acylhomoserine lactone molecules by a bacterium isolated from a Malaysian marine water sample. MALDI-TOF and phylogenetic analysis indicated this isolate BM1 clustered closely to Labrenzia sp. The quorum quenching activity of this isolate was confirmed by using a series of bioassays and rapid resolution liquid chromatography analysis. Labrenzia sp. degraded a wide range of N-acylhomoserine lactones namely N-(3-hexanoyl)-l-homoserine lactone (C6-HSL), N-(3-oxohexanoyl)-l-homoserine lactone (3-oxo-C6-HSL) and N-(3-hydroxyhexanoyl)-l-homoserine lactone (3-hydroxy-C6-HSL). Re-lactonisation bioassays confirmed Labrenzia sp. BM1 degraded these signalling molecules efficiently via lactonase activity. To the best of our knowledge, this is the first documentation of a Labrenzia sp. capable of degrading N-acylhomoserine lactones and confirmation of its lactonase-based mechanism of action.

Quorum sensing enables bacterial to communicate and at the same time control the gene expression in response to the cell density [1]. It is widely used by both gram-positive and gram-negative bacteria to regulate variety of bacterial physiological functions such as biofilm formation [2], bioluminescence [3], virulence factors [4] and swarming [5] which has been shown contribute to bacterial pathogenesis. With this knowledge, the use of QS inhibitor would be a particular value in treating bacterial pathogenicity and infections. In this work we have tested caffeine as quorum sensing inhibitor by using C.violaceum CV026 as a bioassay. This C.violaceum CV026 mutant strain is incapable of producing the purple pigment called violacein unless there are exogenous supply of N-hexanoylhomoserine lactone (C6-HSL) or other short chain AHL .The Inhibitory activity was measured by quantifying violacein production using a spectrophotometer. The results have revealed that Caffeine significantly reduced violacein production in a concentration dependent manner, indicating inhibition of quorum sensing. The presence of caffeine that exhibit anti-quorum sensing activity may be useful as the lead of anti-infective drugs.