Bacteriophage is a virus that plays a crucial role in our lives, as it mostly causes more good than harm. Read more to find out what it is and its impact on our society.
What is bacteriophage?
Discovered by Frederick W. Twort in 1915, and by Felix d’Herelle in 1917, Bacteriophage is a type of virus that infects bacteria. The term bacteriophage means bacteria eater as they have the ability to eat single-celled prokaryotic cells. This type of organism is classified into a number of virus families which include inoviridae and microviridae. They have a simple virus structure that includes genetic material (nucleic acid; DNA or RNA) that is surrounded by a protein coat. The basic structural features of a bacteriophage consist in three different forms; an icosahedral head with tail, an icosahedral head without a tail and a filamentous form.
Life cycles of a bacteriophage.
In an infection a phage would attach to a bacterium and insert its genetic material into the cell, the phage would then follow one of two life cycles.
A lytic phage would take over the cell and make its own phage components, they will destroy the cell and release phage particles. Lysogenic phages would insert their own nucleic acid into the host cell chromosome and replicate without destroying the cell.
In other life cycles such as in pseudolysogeny, the bacteriophage enters the cell but doesn't infect or integrate into the host cell. This occurs when the phage has growth conditions, this role is important in phage survival by preserving the phage until the host cell is advantageous again.
Do they cause harm to humans?
Recent studies have discovered that infectious Phages are found in clinical samples which include ascitic fluid and urine, this suggested that they could reach the peritoneal cavity after they have translocated from the intestines. Their presence in the bloodstream was confirmed after the phages that infect the Bacteroides were discovered in the serum.
In the last century, the process by which DNA is mobilised between cells by a virus or a viral vector was reported in 1952 by Zender and Lenderberg. This led to a great discovery of bacterial DNA in phages which first led to the belief that the methods for segregating the phage and bacterial particles were not accurate enough where either bacteria or free DNA were the ones to infect the phages. Further suspicions have shown that bacterial cells use the capsid genes that they inherit from ancient prophages to build protein capsids to pack and spread their DNA content. The fact that phage capsids can mobilise bacterial DNA has led to many consequences such as; they can mobilise and transduce virulence genes, and antibiotic resistance to new bacterial hosts, which leads to an evolution of new bacterial populations.
Using phages to treat bacterial infections has led to explorations of responses that the phages might cause within the immune system. After the discovery of phages, it was observed that antibodies against the bacteriophages were produced. Non-immunized individuals were seen to present these antibodies against these phages starting at low levels which were known as natural antibodies. This could be a mechanism for removing phages that were circulating the human body and was successful as they were able to rapidly remove wild-type phage λ from the human circulatory system.
Future of bacteriophages
Phage therapy is the use of phages to treat bacterial infections. This type of therapy has mostly existed in Western countries such as the USA, where it has occasionally be used in an emergency basis.
In 2015, Dr Tom Patterson, a professor at USCD School of Medicine experienced a deadly infection while on vacation in Egypt caused by MDR Acinetobacter baumannii, which was incurable by many doctors until his wife, Dr. Steffanie Strathdee stumbled across many articles regarding phage therapy and discussed the likeliness of using this form of therapy as the cure for his infection. A team of researchers at Texas A&M University needed to gather a collection of phages that have been isolated from diverse sources with the addition of newly isolated phages. The allocation ended up being successful and after receiving the many isolated phages and a 9-month recovery, Patterson had made a full recovery.
However, during the last decade, this type of therapy has faced many different challenges as it came to notice that it was part of the growing threat of AMR. One of the challenges faced by this type of therapy is that patients can receive Bacteriophage resistance since in most cases for treatment they receive a cocktail of phages that target bacteria in different ways, meaning that patients need to be constantly monitored to ensure the effectiveness of the phages.
For the future of the phages, Clinical trials are underway like a multi-center phase 1b/2 that assesses the microbiological activity of a single dose of phage therapy in cystic fibrosis patients chronically colonized with P. aeruginosa.
Bibliography
1. The Editors of Encyclopedia Britannica. “Bacteriophage.” Encyclopædia Britannica, 12 Oct. 2018, www.britannica.com/science/bacteriophage.
2. Phage Therapy: Past, Present and Future, Madeline