Antibiotic-resistant pathogens are the next great threat to global health. Many resistant bacteria can transform antibiotic-sensitive individuals into resistant ones through a process known as plasmid-mediated conjugation or horizontal gene transfer (HGT), where genes providing resistance are transmitted directly from one individual to another in the form of a plasmid - a circular piece of DNA - after close contact between cells. Controlling this “bacterial sex” is essential for developing counter-strategies against antibiotic-resistant pathogens.
In a study conducted within the CRI collaborative (Laboratory of Systems Engineering and Evolutionary Dynamics INSERM U1284, University of Paris), published today in PLoS Biology, Alvaro Banderas and Ariel Lindner, along with CRI students Arthur Carcano, Elisa Sia and Shuang Li, show that the pathogenic bacterium Enterococcus faecalis controls the HGT by “estimating” the success of the transfer before investing energy in it. For the transfer to be successful, a plasmid-carrying cell must first encounter a sensitive cell. Estimating transfer success relies on a process called ratiometric quorum-sensing, in which resistant individuals count the number of nearby susceptible cells by “smelling” their pheromones, but also count their own number by doing the same with their own specific self-produced pheromone. Using these two pieces of information, the cells can then estimate the ratio of resistant to susceptible bacteria and ignore changes in total population size. The distinction between these two population parameters (ratio and population size) is crucial, as only the former is a strong indicator of the probability of a successful encounter. It is not enough to know the number of one or other of the two types (resistant or susceptible), as this does not describe the probability that a cell encountered at random is a susceptible cell, unlike the ratio. As in yeast and higher sexual organisms, determining this probability is crucial because activating mating responses, as well as mating itself, is a very costly process. Furthermore, the authors predict that ratiometric quorum-sensing evolves because it confers the best fitness (total number of resistant bacteria in the population) over other possible sensory strategies, while allowing susceptible bacteria to coexist in the same niche. This could be the key to designing probiotic strategies to combat resistant infections.
Read the full article here : https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.3000814
