May 15, 2017Microbiology
Enterococci bacteria are the bane of hospitals, causing thousands of multidrug-resistant infections in patients each year. Now, according to an article published in the journal Cell (11 May 2017), evidence of the bacteria's evolutionary history can be traced back to 425 million. The goal of the study was to understand why, among the vast diversity of gut flora, enterococci are so well adapted to the modern hospital environment. Results showed that based on molecular clock estimation, together with analysis of their environmental distribution, phenotypic diversity, and concordance with host fossil records, place the origins of the enterococci around the time of animal terrestrialization, 425-500 mya. Speciation appears to parallel the diversification of hosts, including the rapid emergence of new enterococcal species following the End Permian Extinction. Major drivers of speciation include changing carbohydrate availability in the host gut. Life on land would have selected for the precise traits that now allow pathogenic enterococci to survive desiccation, starvation, and disinfection in the modern hospital, foreordaining their emergence as leading hospital pathogens
The study examined DNA from 24 species of enterococci, taken from the guts of a wide variety of animal and human hosts. The authors calculated the average rate of genetic change within enterococcal species and compared genes of existing enterococci to those of related, non-enterococci bacteria. The analysis provided the ability to build an evolutionary timeline to estimate when key enterococci traits emerged. The authors then checked this timeline against the fossil record of terrestrial animal evolution. Results showed that all enterococci sampled were resistant to a common set of stresses -- including antibiotics, disinfectants, drying and starvation --suggesting that the ancestors of all enterococci also shared these abilities. Enterococci appear to have developed these traits at around the same time that terrestrial animal life evolved. The authors theorized that the same traits that allow the bacteria to thrive in hospitals likely emerged when they were carried onto land in the guts of the world's first terrestrial animals.
The authors noted that while the model is difficult to prove, it does partially explain the ability of enterococci to survive in hospital environments, as they have long been equipped to thrive in a wide range of challenging environments. According to the authors, having a better sense of what prompted the bacteria to evolve these abilities, could help control enterococci as the bacteria continue to circumvent hospital infection control methods.