Host microbe interactions: a licence to interfere?

Through many millennia of continuous evolution hosts and microorganisms have developed sophisticated and sometimes extremely complex mechanisms of coexisting through symbiosis and mutualism. It is now known that in humans, the population of commensal bacteria on or inside the body significantly outnumbers the host cells. Despite their numerical superiority, microorganisms have adjusted their physiological clocks to benefit themselves and at the same time their host through the maintenance of a healthy state. This very fine and multifaceted balance can be disrupted occasionally through the introduction of pathogens in the commensal bacterial population. The equilibrium is then perturbed to promote dysbiosis and the onset of disease. Through myriads of interactions within their host milieu, bacterial pathogens have developed mechanisms to sense bacterial or host-derived signalling molecules and adjust their physiology accordingly to favour their survival and propagation within their host. At the same time, the host has evolved systems to interfere with bacterial signalling in such a way as to support pathogen clearing and re-establishment of the balance. An example of a captivating interaction is the one involving the catecholamine hormones adrenaline and noradrenaline. This article will summarise the major findings involving host pathogen communication through bacterial or host-derived molecules and discuss ways to take advantage of our potential to interfere with this intricate signalling to profit the host and prolong a healthy life.