Looking backwards to move forward: the utility of sequencing historical bacterial genomes.

Many pathogens which caused devastating disease throughout human history, such as , and , remain problematic today. Historical bacterial genomes represent a unique source of genetic information and advancements in sequencing technologies have allowed unprecedented insights from this previously-understudied resource. This minireview brings together example studies which have utilised ancient DNA, individual historical isolates (both extant and dead) and collections of historical isolates. The studies span human history and highlight the contribution that sequencing, and analysis of historical bacterial genomes have made to a wide variety of fields. From providing retrospective diagnosis, to uncovering epidemiological pathways and characterising genetic diversity, there is clear evidence for the utility of historical isolate studies in understanding disease today. Studies utilising historical isolate collections, such as those from NCTC, ATCC and the Institut Pasteur, offer enhanced insight as they typically span a wide time period encompassing important historical events and are useful for the investigating the phylodynamics of pathogens. Furthermore, historical sequencing studies are particularly useful for looking into the evolution of antimicrobial resistance, a major public health concern. In summary, although there are limitations to working with historical bacterial isolates, especially when utilising ancient DNA, continued improvement in molecular and sequencing technologies, and the resourcefulness of investigators, mean this area of study will continue to expand and contribute to the understanding of pathogens.