Vancomycin-resistant Enterococcus faecium Clone Dominates Danish Hospital Between 2012 and 2020

A recent investigation into a vancomycin-resistant Enterococcus faecium clone at a Danish hospital has shed light on the genetic factors behind its emergence and dominance between 2012 and 2020.

The World Health Organization considers this bacterial strain one of the highest-priority pathogens, due to its ability to transfer resistance genes across different environments and organisms. Its prevalence in hospitals is particularly concerning, as it can spread rapidly through clonal replacement - a phenomenon where high-risk lineages emerge, thrive, and eventually give way to new strains.

Researchers from Instituto de Tecnologia Química e Biológica António Xavier at NOVA University of Lisbon, along with collaborators, have been studying the genetic mechanisms behind the rise and fall of this particular clone. Their findings were published in Genome Medicine, where they detail their investigation into the epidemic's dynamics over nearly a decade.

The study reveals that the vancomycin-resistant Enterococcus faecium clone maintained its dominance due to a stable genome equipped with key plasmids and accessory genes. These genetic components allowed it to adapt to different environments within the hospital, including the gut and surfaces, where it could evade antibiotics and establish itself through biofilm formation.

The researchers observed that during its peak years, this clone rarely underwent DNA recombination - a process known as "shuffling that can introduce new traits and characteristics. This lack of genetic diversity may have contributed to its eventual decline, as other factors eventually took hold and allowed newer strains to emerge.

The emergence of a multidrug-resistant bacterial clone in a hospital has raised questions about the nature of epidemic success. Researchers have found that the clone's dominance was not due to its ability to adapt and change, but rather because it maintained a stable genome.

In fact, when the clone's genome started to diversify, it began to decline in the hospital. This suggests that the initial features that made the clone successful were also those that contributed to its eventual downfall. The genes linked to antibiotic resistance and alternative sugar metabolism, which initially helped the clone thrive, became liabilities as it evolved.

The team has identified a key factor in the clone's success: its ability to produce bacteriocins, small antimicrobial molecules that give bacteria an advantage over their competitors. However, this feature ultimately contributed to the demise of the ancestral clone, allowing newer strains to emerge and take hold.

A genetic super-tool was also found to be present in the bacterial clone. This element combines characteristics of a bacterial virus and a plasmid, allowing it to carry and pass on multiple resistance genes simultaneously.

The implications of these findings are significant for infection control strategies. According to Maria Miragaia, leader of the Bacterial Evolution and Molecular Epidemiology lab at ITQB NOVA, using any one of several antibiotics can select for bacteria carrying a whole package" of linked resistances, including vancomycin resistance.

The emergence of multidrug-resistant bacterial clones in hospitals often goes unnoticed until they have spread widely, according to experts.

By studying the rise and fall of a particular clone in a hospital, researchers can identify its weak points and develop strategies to control similar bacteria in the future.

Targeting the tactics used by the clone to persist could be key to reducing the spread of resistant bacteria. The clone in question employed several strategies to stay ahead, including forming biofilms that protect it from antibiotics.

Understanding these strategies can help healthcare professionals clear multidrug-resistant bacteria from patients and reduce their presence in hospitals.