Studies on the role of horizontal gene transfer in the stabilisation of shared antibiotic resistance within bacterial populations

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Antibiotic resistance is considered one of the biggest threats to global health today. The effective implementation of innovative prevention measures and therapy concepts requires a comprehensive understanding of bacterial resistance mechanisms and their evolution. However, there is currently only little information available on the evolution of sociomicrobiological interactions within bacterial populations that enable survival and outgrowth of genotypically susceptible bacteria during antibiotic therapy. The production of enzymes that inactivate antibiotics confers resistance not only to the producing bacteria but also to non-resistant bacteria in their immediate vicinity. This particular case of cooperative resistance is referred to as shared antibiotic resistance (SHARE). From the evolutionary perspective, SHARE is a manifestation of altruistic social behaviour, because the producing cell spends energy and the susceptible cell benefits from the public goods without sharing the fitness cost. However, it is believed that altruistic resistance traits can only be established in the longer term if mechanisms are developed that either negate the advancement of non-producers or stabilize the development of social traits through social dependency or enforcement. There are many indications that horizontal gene transfer (HGT), i.e. the exchange of mobile genetic elements, plays a central role in the stabilisation of altruistic resistance traits within bacterial populations. However, the role of HGT has not yet been conclusively elucidated in the particular context of SHARE. This research project aims to study the interplay between HGT and the stabilisation of altruistic resistance traits within bacterial populations by the example of plasmids conferring resistance to beta-lactam antibiotics. For this purpose, selected plasmids will be marked with a repressible green fluorescent protein (GFP) tag and introduced into donor strains that constitutively express the corresponding repressor protein. The constructed bio-reporters will be used to study expression rates and HGT frequencies in real time using fluorescence-activated cell sorting (FACS) and high-resolution confocal laser scanning microscopy (CLSM). Moreover, quantitative real-time PCR (qPCR) will be used to measure plasmid copy numbers. The overall research objective is to provide new insights on the role of plasmid transfer and plasmid copy number in the particular context of SHARE and thus making an important contribution to the development of new prevention measures and therapy concepts.