invasion trajectories of human bacterial pathogens

The current framework of resistance of soil microbial communities to invasion relies on the diversity-resistance relationship but it remains unclear whether this mechanism is the main driver whatever the invading species. In order to investigate this issue, we compared the fate of Listeria monocytogenes (Lm) and Klebsiella pneumoniae (Kp) in soil microcosms. Ecoplate experiments suggested that Kp avails of a wider niche breadth than Lm in soil. We used perturbations (freeze-taw or heat cycles) to manipulate soil microbial diversity. Population dynamics were followed over 50 days of invasion while microbial diversity was assessed at times 0, 20 and 40 days. The outcome of invasion was strain dependent and perturbation dependent. The fate of Kp was consistent with the diversity-resistance relationship. Indeed, resistance to Kp invasion was higher under the experimental conditions where autochthonous microbial diversity was the highest while the significant drop of diversity observed during heat perturbation facilitated its persistence. On the opposite, Lm faced stronger resistance to invasion in heat-treated microcosms where diversity was the lowest. Our results show that diversity is not a universal proxy of resistance to microbial invasion, indicating the need to properly assess the array of interactions between the invader and autochthonous communities.