Studies to date concluded that antibiotics at extremely low concentrations can select for resistance mechanisms in single strain experiments. However, these tests barely mimic natural environments where bacteria are embedded within complex communities consisting of thousands of bacterial species. During my fellowship I overcame this limitation and showed that competing with other community members increases an antibiotic’s minimal selective concentration for antibiotic resistance in a bacterial species by more than an order of magnitude. To gain insights into the mechanisms underlying this phenomenon I used mathematical modelling and community wide DNA sequencing analysis to determine resistance gene profiles of the microbial communities. Using these complementary methods, I was able to finally identify two major mechanisms that cause the reduction in selection for antibiotic resistance when embedded in a complex community: First, resistance is more costly to its bacterial host while competing with other community members, and second, other community providing protection to the susceptible strain to withstand the antibiotic pressure more efficiently.
In addition other bacteria in the community can contribute to the spread of AMR by engaging in horizontal gene transfer or “bacterial sex”. Since bacteria propagate asexually, they evolved the ability to exchange genes and hence genetic traits like antimicrobial resistance with each other. During this fellowship I established that bacteria that have been previously exposed to metals are more likely to take up mobile antibiotic resistance genes from their neighbours. Simultaneously, bacteria in freshwater that are living on microplastics are far more likely to gain antibiotic resistance traits through horizontal gene transfer than their planktonic, free-living counterparts. I finally developed a method to visualize, how bacteria can not only accept mobile AMR genes from other bacteria in the community they are living in, but actively mobilize them from their neighbours.
This and other work during this fellowship has led to a total of 8 published or submitted manuscripts so far, with 5 more manuscripts in preparation. I have further presented my research at 4 international conferences, 1 workshop, 1 symposium and was invited to give a research seminar in Australia.
No website has been developed for the project.
