The rise of superbugs is spurring research into alternative ways of fighting resistant bacteria that cause serious infections. One such avenue is a revival of an old idea - using viruses to infect and eliminate bacteria.

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30,000 times magnified image of phages shows some still binding to dead bacteria.
Image credit: Ronen Hazan / Hebrew University

Bacteriophages - or "phages" - are viruses that infect bacteria. Through a long history of co-evolution with bacteria, they have evolved into highly effective "professional killers" of the bugs.

Back in the days when drugs were first developed as a way to treat bacterial infections, scientists were already thinking about using phages to fight bacteria, but then put the idea to one side as antibiotics became successful.

Now, decades later - as we face the daunting prospect of a post-antibiotic era - the idea of using phages or viruses to kill bacteria is receiving attention again.

A good example is a new study from researchers at the Hebrew University of Jerusalem's Faculty of Dental Medicine, who describe their findings in the journal Applied and Environmental Microbiology.

An intriguing fact about the virus the team studied - a phage called EFDG1 - is that they isolated it from Jerusalem sewage.

The study shows that EFDG1 could be an effective way to kill a very stubborn, drug-resistant bacterium called Enterococcus faecalis that can sometimes cause infections following dental procedures.

E. faecalis is a bacterium found in the human gastrointestinal tract. It is a dangerous pathogen that causes endocarditis (potentially fatal heart infection), bacteremia (harmful bacteria in the bloodstream) and other serious infections, such as urinary tract infection, meningitis and - as in the subject of this study - post-treatment root canal infection.

One of the things that makes E. faecalis difficult to treat is because it forms a biofilm - where the bacterial cells cluster and stick to surfaces by excreting a slimy, glue-like substance.

E. faecalis is often recovered from persistent infections associated with root canal treatments, and infection can persist in up to a third of root canals. This high rate of infection limits the choice of treatment options, so researchers are keen to find ways to eliminate E. faecalis, especially when in biofilm form.

The phage almost entirely eradicated E. faecalis in liquid culture and biofilm

For their study, the team tested how well EFDG1 killed E. faecalis cells - both in a liquid culture and in biofilm form. They already knew the phage was capable of infecting the V583 strain of E. faecalis, which is resistant to vancomycin, the most effective antibiotic against the bacterium.

The tests showed EFDG1 almost entirely eradicated E. faecalis - both in liquid culture and biofilm form.

The team also showed EFDG1 was highly effective at eliminating E. faecalis in tissue examples of root canal infection, suggesting that phage therapy using EFDG1 might be an effective way to prevent E. faecalis infection following root canal procedures.

Using transmission electron microscopy and whole genome sequencing, the team also determined that the EFDG1 phage belongs to a subfamily of the Myoviridae phages, which may offer other candidates for treating bacterial infections.

The team also found that the EFDG1 genome does not appear to contain harmful genes, suggesting it may be safe to test its effectiveness at dealing with E. faecalis in humans.

One of the study leaders, Dr. Ronen Hazan, from the Institute of Dental Sciences at the Hebrew University, says:

"As this research shows, bacteriophages may prove an effective tool in the development of much-needed new antimicrobial drugs."

In November 2014, Medical News Today learned of another study reported in the same journal that showed saliva protects teeth against cavities more than we thought. It appears that salivary mucus contains compounds that actively protect teeth from damage by the cavity-causing bacterium Streptococcus mutans.