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A communication strategy among microorganisms using molecular signals known as “quorum sensing” regulates metabolic processes in bacteria depending on their cell density or population size in the environment. Quorum sensing may enable bacteria to transit between a dormant and an active state depending on the concentration of their cells in water. Pathogenic bacteria spread through water depending on their abundance in an active form, and routine detection techniques by culture can detect bacteria in this form only. In the dormant state most bacteria escape detection in routine assays, resulting in a failure to warn against potential disease outbreaks.
The quorum sensing system involves signal molecules called autoinducers which are produced by bacteria and sensed by their neighboring cells. At a certain threshold concentration of these autoinducers, cells switch certain gene expression patterns. Professor Shah Faruque has been collaborating with a number of institutions to strengthen research in this area. The study recently published in PLOS One analyze the quorum sensing system in the cholera pathogen Vibrio cholerae. The natural habitat of these pathogenic organisms is the aquatic environment, and cholera spreads through consumption of food and drinks contaminated with the pathogen. Monitoring the pathogen involves routine testing of natural water samples for the presence and increase in concentration of the cholera bacteria. However, this approach is hindered by the fact that during the period when there are no apparent cholera cases, pathogenic Vibrio cholerae persists in aquatic reservoirs of cholera-endemic areas mostly in the dormant state and fail to be detected by routine bacteriological culture. On resuscitation from this latent state, the bacteria regain the ability to be cultured, but it was not clear which factors derive the resurrection of these dormant cells.
Professor Shah Faruque’s recent paper uses cutting-edge techniques to show that that certain variant strains of environmental V. cholerae vastly overproduce a chemical signal called autoinducer AI-2, which produces a wake up call for the dormant bacteria in water. This phenomenon was then confirmed by testing various laboratory generated mutants as well as by determining the relevant gene sequence of naturally occurring strains which overproduce AI-2 in their culture. Environmental water samples which were found to be negative for pathogenic V. cholerae in routine enrichment cultures were selected to test whether Vibrio cholerae could be recovered from such apparently negative water samples after treatment with the autoinducers produced by the mutant strain. These experiments showed conclusively that the signals do indeed resuscitate dormant V. cholerae cells in water samples when cultured in the presence of AI-2 produced by the mutant strains.
The implications of these findings are manifold. On the one hand it provides a method for overproducing an autoinducer and use it to develop improved methods for water testing. Perhaps even greater implication is in understanding a natural process which might contribute to resuscitation of dormant pathogenic microorganisms in water and initiate epidemic outbreaks. Adequate monitoring strategies, using improved detection methods can be a predictive indicator for cholera outbreaks ahead of time. Furthermore, such phenomenon might also be applicable for other waterborne diseases, beyond cholera per se.
A remarkable aspect of this research is that it was done through informal collaborations among researchers from multiple private universities in Bangladesh under the leadership of Professor Faruque, thus creating an example of sharing research facilities and resources to conduct cutting edge research in Bangladesh. He also collaborated with Osaka Prefecture University, Japan for obtaining advanced molecular technology.