Introduction To Phage Therapy


Bacteriophages are viruses which are found naturally in the environment. They use bacterial cells to replicate, destroying the bacteria in the process. “Phages” provide an alternative to antibiotics and they may be the solution to antibiotic resistance. This article gives a brief overview of the history of phage therapy, their mechanism of action, risk and benefits.

Phages, or bacteriophages are viruses that invade bacterial cells. Bacteriophages have the ability to target and destroy bacteria. They can be relatively narrow in their spectrum of effect, targeting only one strain of bacteria or only a small number, unlike most antibiotics. Phages have been used in medicine for about 100 years. For a lot of that time they have been used only in small geographical pockets, mainly Poland and the Soviet Union (primarily Georgia). The approaching disaster of antibiotic resistant infection, combined with the increasing understanding of damage from antibiotics, due to their non-targeted nature, has led to increasing interest in phage therapy. The field of phage therapy has been hampered by regulatory hurdles and a lot of the reporting of scientific data on phage therapy is not up to modern standards. There is, however, enough data to infer that the phage therapy may be beneficial in the treatment of bacterial infectious diseases.

History

In the 1890s a British bacteriologist known as Ernest Hankin was surprised to find that a number of rivers in India processed antibacterial properties. The waters of the Ganges and Jumna seemed to limit the spread of cholera. The unidentified antibacterial agent was almost certainly bacteriophage. A number of other observations around the same time period indicated phage activity. It seems that it was an English man, Frederick Twort, a couple of decades later who first suggested that the antibacterial effect may be due to viral activity. Felix d’Herelle, a Canadian microbiologist at the Institut Pasteur in Paris coined the term bacteriophage around that time (1915-1920). The name was formed from the Greek and means to eat or devour bacteria.

d’Herelle First observed bacteriophage activity in 1910 while studying locust control in Mexico. Phages are used to treat bacterial problems in animals, insects, fungi and plants. d’Herelle was part of an investigation into an outbreak of hemorrhagic dysentery in France in 1915. The bacteriologist created bacteria free filtrates from the faecal samples of the soldiers afflicted by the outbreak. After inoculating the filtrates with shigella, a bacteria which causes dysentery, and spreading the infected filtrates on a growing medium, d’Herelle observed the creation of clear patches in the medium, patches which he understood to be created by viruses destroying shigella bacteria. d’Herelle had filtered the naturally occurring phages in the environment and shown that they can destroy shigella. Phages have since been used extensively to prevent and treat dysentery.

d’Herelle then worked on bacteriophage selection and production. He tested bacteriophage on himself and his colleagues first before using it on patients in the hospital. His early uses of phage therapy were reported later, the first reports in the literature came from Richard Bruynoghe and Joseph Maisin in the treatment of a skin based staphylococcal infection. Bacteriophage production happened ona  large-scale in many countries in the next two decades. Eli Lilly produced seven phage preparations in the United States.

Phage therapy remained quite controversial, its efficacy was, and still is questioned. This is in part due to its specificity. Bacteriophages are usually pretty limited in the type of bacteria that they destroy, the selection of the correct phage is key to its efficacy. Many studies and uses are unlikely to have selected the correct phage. Some of the better studies show 70-100% efficacy, even and often in cases of antibiotic resistance. With the mass production of penicillin in the early 1940s phage therapy was phased out in many parts of the world.

In 1923 Felix d’Herelle, together with Giorgi Eliava founded the Eliava Institute in Georgia. The Institute became the main home of phage therapy for much of its history. Eliava was executed by the NKVD in 1937 and d’Herelle, who was in France at the time, did not return to the Institute. The Institute survived and at times produced several tonnes of bacteriophage medicines per day. The Soviet Union used phage therapy until just prior to the fall, much of it used for prevention of dysentery in The Red Army. Poland has a relatively long and constant history of phage therapy centered around Wroclaw. France had commercial phage therapy from 1919 through to 1979, and the Pasteur Institut produced small amounts into the 1990s. In the last 10-20 years phage therapy has slowly increased it’s geographical reach again, notably in Australia, Canada, France, Germany, and the USA. Trials have been conducted in the in the US and UK.

Mechanism

Bacteriophages are viruses – complex molecules of non-living infectious agents which require host cells for growth and replication. What differentiates bacteriophage from other viruses is that they only attack bacteria. Bacteriophages are subdivided into two main categories, lytic and lysogenic. These subcategories are defined by the life-cycle of the bacteriophage. One of the primary differences between lytic/virulent phages  and lysogenic/temperate phages is the ability of the lysogenic phage to incorporate a copy of the phage genome into the genome of the host bacterium. This exchange of genetic material by lysogenic phages carries a risk of modifying a bacterial infection. This can lead to transfer of genes across bacteria, increasing bacterial toxins or antibiotic resistance. Lysogenic phages are generally excluded for this reason. Lysogenic phages may remain somewhat dormant within the genome of the target bacteria while it replicates (both bacteria and incorporated phage). The second category – lytic phages – do not incorporate genetic material into bacteria. Lysis is the process of breaking down the cell membrane. Destruction of the cell membrane leads to the death of the bacterium. Though both types of phage can and do lyse cells, lytic phages are selected for their safety and the fact that there generally more efficient at lysis.

The lytic cycle may be the main mechanism of action in phage therapy. It is believed that the tail of the bacteriophage binds to a specific receptor on the surface of the bacteria. This tail is then used to inject DNA into the bacterial call. The material of the bacteria is then used to synthesise and assemble new bacteriophages. Finally, the bacteriophage creates proteins which destroy the cell membrane. It is this final stage of lysis which is believed to be the antibacterial mechanism of bacteriophages. The release of new phages from the now dead bacteria allows amplification of phage numbers and thus the antibacterial effect. In theory, higher bacterial count will lead to increased replication of bacteriophage. Typically hundreds of new phages are released during process of lysis, called a phage burst. There are a number of other mechanisms which employ phages, for example, they can used to deliver (other) antibiotic materials in a targeted manner to bacteria. Generally bacteriophage therapy is based around the process of lysis (at least in theory). There are dissenting voices about most of the claims of phage therapy, including their mechanism of action.

Advantages

Bacteriophages can target only only one or a few strains of bacteria. This characteristic of phage therapy makes it superior to antibiotics in treating bacterial problems in regions where there is a beneficial bacterial microbiome, for example within the gastrointestinal tract or on the skin. Selection of the correct phage could weed out the problematic bacteria within the gut or skin microbiome without causing the dysbiosis/imbalance that is seen with antibiotics.

Antibacterial resistance is a serious and growing problem. While bacteria can become resistant to phage therapy this resistance is unrelated to antibiotic resistance. Phage therapy represents a viable treatment forrantibiotic resistant infections. Bacteriophages are usually found in the environment where those bacteria exist, in untreated sewage, standing water, soil, and so on. When phage resistance occurs it is common for a new phage to quickly develop in the environment in response to the newly resistant bacteria. Phage resistance can be overcome quite quickly by identification of the relevant phase in the environment, quickly relative to antibiotic development at least.

Another advantage of phage therapy is the  manner in which phages travel through tissues and replicate. Fibrous, necrotic, or weeping tissue can be very difficult to get sufficient antibiotics in contact with the body of the infection. Whereas, phages will replicate on the bacteria in the surface and pass through necrotic tissue finding the bacterial infection below. Phages seem to travel rapidly to most parts of the body, allowing treatment bone and brain tissue. Jazz musician Alfred Gertler was famously treated with phage for an antibiotic resistant infection which had colonised the bone of his ankle.

Though phage therapy does not carry many of the risks associated with antibiotic treatments in themselves there is potential to create of the same problems secondary problems that antibiotics can create, for example the acute release of endotoxin/lipopolysaccharide from bacteria which can lead to problems like herxheimer reaction or sepsis.

Risks

Temperate (or Lysogenic) bacteriophages are generally excluded from therapy because of their potential to allow bacteria to exchange DNA leading to antibiotic resistance or increased production of bacterial toxins. Cholera is a disease caused by the production of bacterial toxin in some strains of the bacteria, the transmission of toxin producing genes from different strains of the bacteria occurs by interaction with a lysogenic phage. Cholera outbreaks may be initiated by lysogenic phages and limited by lytic phages. It has also been theorised that lysogenic bacteria changed corynebacterium into the (exo)toxin producing strain which causes Diptheria.

As mentioned above even lytic phages have the potential to cause sepsis. Sepsis is an inflammatory/immune response that can occur in response to endotoxin,which is a part of gram-negative bacteria. A release of large amounts of endotoxin into the system from bacterial lysis could cause death and is likely to at least trigger herxheimer reaction. This is also a risk with antibiotics. It’s not something that I have seen reported in literature though there is discussion over modulating the rate of lysis in cases where it is necessary to attack endotoxin containing bacteria. Other phage tactics can destroy endotoxin containing bacteria without lysis, avoiding herxheimer and sepsis altogether. As phages are initially sourced from waste material they must be properly purified in order to remove harmful elements like bacteria and endotoxin.

Another consideration with phage therapy is the immune response. Phages are detected by the immune system and there is an action to remove them. Phages, taken orally, are easily detectable for a number of hours before the numbers fall, though that is dependent on many factors. There is a possibility of creating immune problems from phage therapy, phase antibodies are produced in response to the viruses. This is a consideration discussed in the literature, length of phage therapy is an important risk factor here. Though the risk is pretty low.

The specificity of phage therapy is both a strength and a weakness. In order to treat a given infection you have to have the right phage, this means correctly diagnosing the infection. Alternatively, multiple strains of phages can be combined in order to address the most common bacterial strains causing disease in a given region. Whether using targeted phage therapy or a phage cocktail approach it is key that the appropriate phage be used. Antibiotics are often more broad in their effect. There are a number of other considerations regarding purification of materials used to create phage medicines. These processes seem very well understood at this point and should not pose a risk from phage therapy when purchased from a competent supplier.

In the time between writing this article and posting it phage therapy has popped up in the science press.

Click Image For Story

A bacteriophage cocktail targeting Escherichia coli reduces E. coli in simulated gut conditions, while preserving a non-targeted representative commensal normal microbiota

There are a number of phage products available without a prescription, many of them contain the same 4 phages and include probiotic bacteria.
Some products contain only phages – Nutrivee Advanced Prebiotic – Amazon

I’ll be looking at phage therapy in more depth in future articles.

Further Reading:
The ‘Nuts and Bolts’ of Phage Therapy
Bacteriophage Therapy
Bacteriophages – Khan Academy (The lytic and lysogenic cycles)
Cholera Phage Discovery
The Forgotten Cure: The Past and Future of Phage Therapy (Amazon)
Phages Of Life–The Path To Pharma