Novel Lytic Enterococcus Phage as a Biocontrol Strategy for Multidrug-Resistant Enterococcus faecalis Biofilms on Food-Contact Surfaces: Genomic and Functional Insights

In the hidden world of food safety, a persistent problem lurks on the surfaces of dairy processing plants. It is not a single bacterium, but a community of them, living together in a slimy, protective layer known as a biofilm. These communities are formed by bacteria like Enterococcus faecalis, which are naturally tough and can survive in harsh conditions, from high heat to salty environments. Once they stick to stainless steel equipment and build these biofilms, they become incredibly difficult to remove. Standard cleaning chemicals often fail because the slime acts as a shield, protecting the bacteria inside. This is a major concern because these bacteria can carry antibiotic resistance, making them dangerous to human health, and they can spoil food or contaminate the production line. Scientists have long searched for a way to break these shields without using harsher chemicals that might damage the equipment or the food itself.

A team of researchers from Egypt and Japan has turned to nature's own predator to solve this problem: the bacteriophage. These are viruses that specifically hunt bacteria. Unlike the viruses that infect humans, bacteriophages only target bacterial cells. They work by attaching to a bacterium, injecting their genetic material, and turning the cell into a factory that produces more viruses until the cell bursts open and dies. The researchers isolated two of these viruses from sewage samples, looking for ones that specifically target the troublesome Enterococcus faecalis. They found two candidates, named BV26 and BV34, and set out to see if they could survive the tough conditions of a dairy plant and effectively wipe out the bacterial biofilms.

The researchers first examined the physical appearance of these viruses using powerful electron microscopes. They discovered that both viruses belong to a family characterized by a hexagonal head and a long, flexible tail, resembling a tiny syringe waiting to strike. They then tested how well these viruses could survive in different environments. The results were promising. The viruses remained active across a wide range of acidity levels, from very acidic to very alkaline, and they could withstand temperatures up to 50 degrees Celsius. Perhaps most surprisingly, they were not harmed by ultraviolet light, a common method used to sterilize surfaces. This meant that these viruses could potentially be used in facilities that rely on UV light for cleaning, as the viruses would not be killed by the process.

To ensure these viruses were safe to use, the team sequenced their entire genetic code. They were looking for any signs that the viruses might carry harmful genes, such as those that cause disease or make bacteria resistant to antibiotics. The analysis showed that the viruses were purely lytic, meaning they only destroy their hosts and do not integrate into the bacterial DNA to lie dormant. Crucially, the genetic map revealed no virulence factors or antibiotic resistance genes, confirming that the viruses are safe for use in food production environments. The genetic study also showed that one of the viruses, BV26, was distinct from other known viruses, representing a new lineage in the family of Enterococcus hunters.

The team then moved to the most critical test: could these viruses actually stop the bacteria from forming a biofilm or destroy one that was already there? They grew the bacteria on stainless steel coupons, which simulate the metal surfaces found in dairy equipment. When they applied the virus to prevent the bacteria from sticking, they found that the effect depended on the number of viruses used. At the highest concentration, the virus prevented the bacteria from forming a significant biofilm, reducing the bacterial count by more than three orders of magnitude over five days. This means that instead of millions of bacteria, only a few thousand remained.

Even more impressive was the virus's ability to clean up an existing mess. The researchers allowed a mature biofilm to grow on the steel for five days, creating a thick, established layer of bacteria. They then applied the virus and watched what happened over the next 24 hours. Within just one day, the virus had reduced the number of bacteria in the mature biofilm by nearly seven orders of magnitude. This is a massive reduction, effectively erasing the vast majority of the bacterial colony that had taken days to build. The virus did not just stop the bacteria from growing; it actively dismantled the existing community.

The study concludes that this specific virus, BV26, is a robust and effective tool for food safety. It is stable enough to survive the varying conditions of a dairy plant, safe enough to use without fear of spreading resistance, and powerful enough to both prevent and eliminate stubborn bacterial films on metal surfaces. While the researchers note that more testing under real industrial conditions is needed, the findings suggest a new, natural way to keep food processing equipment clean. By using a virus that specifically targets the problem bacteria, the industry may be able to maintain higher hygiene standards without relying solely on chemical disinfectants that the bacteria have learned to resist.