The Pseudomonas Quinolone Signal (PQS) Balances Life and Death in Pseudomonas aeruginosa Populations

When environmental conditions deteriorate and become inhospitable, generic survival strategies for populations of bacteria may be to enter a dormant state that slows down metabolism, to develop a general tolerance to hostile parameters that characterize the habitat, and to impose a regime to eliminate damaged members. Here, we provide evidence that the pseudomonas quinolone signal (PQS) mediates induction of all of these phenotypes. For individual cells, PQS, an interbacterial signaling molecule of Pseudomonas aeruginosa, has both deleterious and beneficial activities: on the one hand, it acts as a pro-oxidant and sensitizes the bacteria towards oxidative and other stresses and, on the other, it efficiently induces a protective anti-oxidative stress response. We propose that this dual function fragments populations into less and more stress tolerant members which respond differentially to developing stresses in deteriorating habitats. This suggests that a little poison may be generically beneficial to populations, in promoting survival of the fittest, and in contributing to bacterial multi-cellular behavior. It further identifies PQS as an essential mediator of the shaping of the population structure of Pseudomonas and of its response to and survival in hostile environmental conditions

Potential therapeutic applications of microbial surface-activecompounds

Numerous investigations of microbial surface-active compounds or biosurfactants over the past two decades have led to the discovery of many interesting physicochemical and biological properties including antimicrobial, anti-biofilm and therapeutic among many other pharmaceutical and medical applications. Microbial control and inhibition strategies involving the use of antibiotics are becoming continually challenged due to the emergence of resistant strains mostly embedded within biofilm formations that are difficult to eradicate. Different aspects of antimicrobial and anti-biofilm control are becoming issues of increasing importance in clinical, hygiene, therapeutic and other applications. Biosurfactants research has resulted in increasing interest into their ability to inhibit microbial activity and disperse microbial biofilms in addition to being mostly nontoxic and stable at extremes conditions. Some biosurfactants are now in use in clinical, food and environmental fields, whilst others remain under investigation and development. The dispersal properties of biosurfactants have been shown to rival that of conventional inhibitory agents against bacterial, fungal and yeast biofilms as well as viral membrane structures. This presents them as potential candidates for future uses in new generations of antimicrobial agents or as adjuvants to other antibiotics and use as preservatives for microbial suppression and eradication strategies

Bacterial Quorum Sensing: Biofilm Formation, Survival Behaviour and Antibiotic Resistance

Biofilms are association of microorganisms that attach to each other to a surface enclosed in a self-generated extracellular matrix. Virtually (99.9%) all microorganisms have the competence to form biofilm. The formation of biofilm is a complex process, in which bacterial cells transform from planktonic cells to sessile mode of growth. The biofilm development results from the expression of specific genes. Biofilms have been developed as an adaptive strategy of bacterial species to survive in adverse environmental conditions as well as to establish antagonistic or beneficial interactions with their host. Molecular interaction and details of biofilm formation are not well-understood as bacteria in the biofilm have several orders of magnitude, more resistant to antibiotics compared to planktonic bacteria. Thus, the currently available drugs typically failed to target bacterial biofilms. Quorum sensing (QS) is a process of intercellular signalling or cell-cell communication and a vital regulatory mechanism for coordinating biofilm formation including common activities and physiological processes such as symbiosis, formation of spores or fruiting bodies, antibiotics synthesis, genetic competence, apoptosis and virulence in many bacterial species using extracellular QS signalling molecules, which is often referred to as autoinducers (AIs). Microorganisms produce a wide variety of QS signalling molecules that can be self-recognized in a concentration-dependent manner and subsequently induce or suppress expression of QS-controlled genes. Bacterial QS regulation is established through a wide range of signals such as oligopeptides, N-acyl homoserine lactones (AHLs), furanosyl borate, hydroxy palmitic acid methyl ester and methyldodecanoic acid. In this chapter, we highlight the current understanding of the processes that lead to bacterial biofilm formation, survival behaviours and mechanisms of antimicrobial resistance in bacteria