Figure 1: Quorum sensing-inhibitory effect of essential oil of Ferula asafoetida.

Pathogenic bacteria develop antibiotic-resistance at a pace much faster than the pace at which new antimicrobials can be discovered and introduced into the market. The process of new drug development demands identification of novel targets in the pathogenic population. Conventional antibiotics have largely targeted bacterial cell wall synthesis, protein synthesis, or nucleic acid synthesis. However in recent years, quorum sensing (QS) machinery of the pathogenic bacteria has received considerable attention as potential target of novel anti-infective agents. QS is the mechanism through which microbial populations modulate their behaviour in a cell-density dependent fashion. In many of the pathogenic bacteria, a considerable number of theirgenes (including those associated with virulence) are QSregulated. As pigment production in many of the pathogenic bacteria like, Staphylococcus aureus, Pseudomonas aeruginosa etc. is controlled by QS, understanding the genetics underlying pigment production becomes important in clinical context. For example, in Chromobacterum violaceum , production of the violet pigment violacein is under regulation of the vio operon; and the region of its genome coding for one of the important virulence traits i.e. haemolysis is located very much near to this vio operon. Screening assays for identifying novel QS-inhibitors find pigment production as one of the most convenient test parameters.

Figure 1 displays results of our preliminary investigation on QSinhibitory potential of the Ferula asafoetida essential oil extracted from its latex employing a microwave based extraction method. This oil was able to reduce QS-associated production of the purple pigment violacein in Chromobacterium violaceum ; and the blue pigment pyocyanin in Pseudomonas aeruginosa . Pyocyanin is one of the virulence factors of the notorious bacterium P. aeruginosa [1]. The operon which regulates production of violacein contains five genes vio A-E [2]. Pyocyanin is synthesized from chorismate by the phz operons, and the pathway involved is positively regulated by the transcriptional activator MvfR (PqsR) through the synthesis of quorum-sensing quinolone molecules [3].

Information regarding the genetics of pigment production in bacteria can be helpful in formulating novel anti-virulence strategies to reduce production of QS-regulated virulence factors including pigments. Screening exercises for Identification of the natural products possessing potent QS-modulatory property may result in finding novel leads for development of new anti-infectives.