Genomic Characterisation of Poultry-Derived Enterococci in the Czech Republic: Insight into Virulence and Antimicrobial Resistance

In the hidden world of the gut, tiny bacteria called enterococci live alongside humans and animals. These are not usually dangerous invaders; they are common residents of the digestive system, found in soil, water, and food. However, they have a notorious reputation in medicine because they are exceptionally good at learning how to survive attacks from antibiotics. When these bacteria acquire the ability to resist drugs, they become difficult to treat, posing a risk to both animal and human health. Scientists have long known that farms are places where these bacteria thrive, but the full picture of what these specific strains carry—their genetic blueprints for survival and their ability to cause disease—has remained unclear in many regions. Understanding exactly which genes these bacteria possess is crucial, because it reveals how they might spread resistance from the farm to the wider environment.

A team of researchers in the Czech Republic recently took a close look at these bacteria to see what they were carrying. They collected samples from chickens on twelve different farms, taking swabs from day-old chicks, older birds, and even the barns themselves. In total, they gathered 47 distinct samples of enterococci. Instead of just looking at how the bacteria reacted to antibiotics in a test tube, the scientists decoded the entire genetic instruction manual of each sample. This process, known as whole-genome sequencing, allowed them to see every single gene the bacteria possessed, including the specific instructions for resisting drugs and the tools they use to stick to tissues or form protective layers.

The study revealed a diverse community of bacteria. Most of the samples belonged to a species called Enterococcus faecalis, but the team also found Enterococcus faecium, Enterococcus gallinarum, and Enterococcus cecorum. When they mapped out the genetic family trees of these bacteria, they found 19 different types, known as sequence types. Three of these types had never been seen before and were added to the global database of bacterial genetics. This discovery suggests that the bacterial populations in Czech poultry are constantly evolving and are more varied than previously thought. The researchers also found that some of these new types carried unique combinations of genes, hinting that these farms might be breeding grounds for new genetic lineages.

The most significant finding concerned the bacteria's ability to resist medicine. The researchers found that the bacteria carried a wide array of genes that protect them from common antibiotics, including those used to treat infections in both animals and people. The most common resistances were against tetracyclines, macrolides, and lincosamides. In many cases, a single bacterium carried instructions for resisting multiple different classes of drugs at once. This is known as multidrug resistance. The study showed that the E. faecalis isolates were the most heavily loaded with these resistance genes, with some carrying up to nine different types of resistance instructions. This confirms that poultry can act as a reservoir, holding onto these dangerous genetic traits.

Beyond resistance, the team also looked for genes that make bacteria dangerous, known as virulence factors. These are the tools bacteria use to stick to a host, form protective communities called biofilms, or evade the immune system. The E. faecalis bacteria were found to carry a large number of these virulence genes. Many of them had the instructions to build biofilms, which are slimy layers that help bacteria survive on surfaces and resist cleaning. They also carried genes that allow them to sense each other and coordinate their behavior, a system that helps them establish infections. The most virulent strains carried between 24 and 35 different virulence genes, suggesting they are well-equipped to cause disease if they move from the farm to a vulnerable host.

One specific finding offered a reassuring note. The researchers looked for genes that confer resistance to vancomycin, a powerful antibiotic often used as a last resort for serious infections. They found no evidence of the high-level resistance genes that make vancomycin useless. The only resistance to vancomycin they found was in the E. gallinarum samples, which carry a natural, low-level resistance that is built into their species and cannot easily spread to other bacteria. This aligns with broader trends in Europe, where the ban on a specific growth-promoting antibiotic decades ago has successfully reduced the presence of highly resistant bacteria in poultry.

The study concludes that while the chickens in the Czech Republic are not currently carrying the most dangerous, high-level drug-resistant strains, they are still a significant source of bacteria with the potential to cause trouble. The bacteria found there are diverse, carry many resistance genes, and possess the tools to cause infection. The presence of new genetic types and the high number of resistance genes suggest that these farms are active environments where bacteria are constantly adapting. The researchers emphasize that this highlights the need for continued monitoring and the careful use of antibiotics on farms to prevent these bacteria from becoming a bigger problem for public health.