Quorum quenching – an alternative antimicrobial therapeutics Sunita Adak, Lakshmishri Upadrasta, S.P. Jeevan Kumar, Rahul Soni, Rintu Banerjee* Department of Agricultural and Food Engineering, Indian Institute of Technology, Kharagpur- 721 302, West Bengal, India New millennium is witnessing an alarming increase in multi-resistant microbes due to the indiscriminate application of compounds to kill/inhibit growth of microorganisms. Consequently infections that were once treatable have become non- treatable. Microbial resistance to traditional antimicrobials and the sparse availability of novel antimicrobial agents necessitate exploration of alternative therapies. Quorum Sensing (QS) signaling systems represent highly attractive targets for the development of novel therapeutics that may prevent, suppress, and/or treat infectious diseases. The present chapter deals with the mechanisms and key components of quorum sensing. It represents an overview of quorum quenching strategies. Attempt to cite substantial studies on small quorum sensing inhibitors, their probable sources, and mechanism as novel antimicrobial agents against different pathogens has also been made. Key words: Quorum sensing; microbial resistance; quorum quenching; antimicrobial therapeutics 1. Introduction Invasion and colonization of one organism in another for multiplication is a natural process of evolution. It is a conventional process employed by microbes for their sustenance and survival. This forms the basis of infection in multicellular organisms. Not all invading microorganisms are infectious in nature. Some are found to lead a symbiotic association with the host cells. These may even be protective in nature. Microbes which infect and subsequently lead to fatal diseases are of major concern for human beings. Such infecting microbes include bacteria, fungi, mycoplasma, viruses, protozoa etc. Though, several treatment strategies have been employed for their eradication the discovery of antibiotics has been a landmark in the history of medicine. With the introduction of antibiotics, a new era of therapeutics had started which promised to be a potential tool for abolition of infectious diseases caused by bacteria. Consequences of the use of antibiotics turned out to be partially fruitful. Indiscriminate use of antibiotics leads the way for the evolution of superior kind of microbes which are no longer sensitive to antibiotics i.e. antibiotic resistant microbes. Emergence of resistant microbes forced human beings to search for better and effective therapeutic alternatives that are more secure with respect to long term effect. Intensive research in microbial systems, their organization, and mutual interaction with each other during colonization and subsequent infection, showed the presence of a kind of communication predominant in multicellular systems. This communication which is known as quorum sensing (QS) involves secretion of certain molecules and their detection. Presently the research activities are oriented towards treating diseases caused by microbial infection by disconnecting this communication- quorum quenching (QQ). The present chapter focuses on the various aspects of quorum quenching and its potential role in treatment of infectious diseases, along with the challenges faced in such approach. 1.1Basics of Microbial Infection Infection and disease relationship of a particular microbe in a host is governed by various factors. Study of some of the underlying factors is essential to understand the mechanism of infection leading to disease. Infection involves successful multiplication of microbes in a host by utilizing host origin molecules as resources. But all infections don’t lead to diseases, even in case of a pathogenic microbe. For manifestation of disease, couple of tens of thousands to millions of microbes (bacteria) are needed i.e. a significantly high number, which makes their easy and rapid elimination by the host defense mechanism difficult. Along with it host immune status is also an essential factor which determines the extent of infection. Certain specific biological features of microbes like, presence of capsule, flagella etc. play an important role in the pathogenicity of a microbe and even determine its virulence. Sequence of steps eventually leads to infection. Microbial infection follows the given pathway-  Adhesion- This most crucial part of infection involves interaction between pathogenic microbe and host cell or tissue. It involves attachment using adhesins, fimbriae, pili etc. besides some exceptions.  Penetration- In most cases adhesion is followed by penetration of host cell and/ or tissue by the bacteria as found in E.coli, Salmonella etc. 586 ©FORMATEX 2011 Science against microbial pathogens: communicating current research and technological advances A. Méndez-Vilas (Ed.) ______________________________________________________________________________