Image caption The therapy can be injected, sprayed on to the site of infection or swallowed

They might look like sinister aliens, but these bacteria-munching viruses could be the next weapon in the fight against infectious diseases.

At the Eliava Institute in Tbilisi, Georgia, patients are treated for all kinds of bacterial infections with viruses called phages. In most places in the world antibiotics are given for these infections.

One patient says he regularly uses phages to treat a recurring eye infection.

"I've tried everything. I've even had operations on my eye but nothing helped. But this does help," he says.

Phages are naturally occurring viruses that kill bacteria. Once they get into bacterial cells the phages' DNA replicates until it kills the host.

Doctors in Georgia, and in other countries that were in the former USSR, have been using this therapy for 90 years. But medics and drug regulatory bodies in most places in the developed world have been reluctant to accept that it works.

Now that more and more bacteria have become resistant to antibiotics, the pharmaceutical industry is showing an interest in phage therapy.

Image caption The phage hijacks the bacterium, turning it into a phage factory

The director of the Eliava Institute, Dr Revaz Adamia, explains: "In 2008 I had six letters from people in the West asking for help, but now in the last two months I've probably had about 150.

"People want to be cured because they are desperate that they cannot be cured with antibiotics. Now they are looking at what they can do and they are coming to us."

Viral broth

Dr Martha Clokie, a microbiologist at the University of Leicester, carries out research into phages that could treat Clostridium difficile infections. She has tried therapy at the Eliava Institute.

"When I was in Tbilisi one winter I had tonsillitis, and every six hours I was given broth containing phages, which I gargled. Back in the UK my husband and child had the infection too and they were prescribed antibiotics. We all got better at the same time."

Analysis The need for new treatments for bacterial infections is desperate. From tuberculosis to E. coli, Klebsiella to gonorrhea, resistance to antibiotics is rising fast. Health officials around the world have warned that we may be entering a post-antibiotic era. It could mean deadly diseases become untreatable while surgery and cancer therapies would carry enormous risks of patients catching untreatable infections. Phages are one of the options that are often suggested as a possible new weapon against bacterial infection. It is an appealing idea - the enemy of my enemy is my friend. However as far as mainstream medicine is concerned it is just an idea. The field has not had the same level of funding as drug development. It means the big questions of effectiveness and safety still remain largely unanswered. Analysis: Antibiotic apocalypse The drugs don't work - so what will?

The institute also has some prepared phage solutions that it has worked out will kill the bacteria that cause common diseases, such as E.coli, which causes stomach upsets.

The therapy can be injected, sprayed on to the site of infection or swallowed. Each solution contains many types of phages, although usually just one attacks the bacteria.

Refrigerators

Dr Naomi Hoyle is an American who has trained to be a doctor in Georgia and now works at the institute.

She is married to the grandson of Dr Liane Gachechiladze, one of the scientists who kept the place going during the civil wars and economic chaos of the 1990s, following the collapse of the Soviet Union.

Dr Gachechiladze remembers: "We used to get a lot of power cuts in this neighbourhood which was a problem because phages have to be stored cold in refrigerators.

"But in the part of town where I lived, we would still often have electricity. So I bought an old fridge, and I used to take all the phages home and keep them safe in my kitchen."

Dr Hoyle says that one of the advantages of the viruses over antibiotics is that they target only the harmful bacteria.

"It doesn't have the side-effects or the negative aspects of antibiotics, like diarrhoea, because of its high specificity. It's not the silver bullet that antibiotics are, but it has its advantages as it works well on chronic infections. It enters the site and continues to do its work even after application."

Dr Martha Clokie says we may see the use of phage therapy outside the former Soviet Union in the next decade. "Large companies have done phase one and two clinical trials and are now finding ways to do phase three clinical trials, in which they will be seeing if the treatment works in patients.

"In the future we may see phages used to treat minor bacterial infections, and antibiotics kept for the serious life-threatening conditions."