T-phages are among the viruses that have specialized in the infestation of bacteria and are therefore called macrophages or simply phages. Each type of phage is specialized in each case for the infection of a specific bacterium. The tailed T-phages (the T derives from the English 'tail') are aligned to the infestation of the intestinal bacterium Escherichia coli.
The 7 known T phages designated T1 to T7 belong to the three families siphoviruses (T1, T5), podoviruses (T3, T7) and myoviruses (T2, T4, T6). The even and odd T phages each differ in several common features.
T phages are characterized by a complex structure. The main components are base plate, injector and head. On the base plate are so-called spikes, with which the phage can cling to the bacterial wall and stab in it. The injection device consists of a contractile tube through which the DNA of the phage is "shot" into the coli bacterium. The double-stranded DNA is located in the head of the T-phage and, after docking to the bacterium, is transported through the contractile tube of the injection apparatus into the interior of the coli bacterium. After infection, the parts of the T-phage remaining on the outside of the sheath are no longer needed and detach again from the bacterial wall.
T-phages, like other phages, are usually found where bacteria are present. In effluents and stagnant waters, where normally a huge and differentiated association of bacteria takes place, bacteriophages also occur in a similarly accumulated and differentiated form. Similar conditions can be found even in the extremely clean appearing oceans.
In the human body, T-phages can be found mainly in the places populated by coliform bacteria. In healthy people with an intact immune system, this is primarily the digestive tract. T-phages that get lost in the bloodstream are recognized by the immune system and trigger an immune reaction that leads to the destruction of the phages. There is hardly a direct risk of infection with T-phages, since they are not independent pathogens. With correspondingly weak immune defense, it is only conceivable that T phages cause a sensitive thinning of the coli bacteria within the intestinal flora.
T-phages used for therapeutic purposes can be lyophilized without losing their physiological properties.
T-phages, which can only infect and kill coliform bacteria, play only a minor role in the human body. Conceivable, however, would be a targeted use against pathogenic Coli bacteria outside the digestive tract. In contrast to antibiotics, which have a broad-band effect, thus also destroy a multitude of useful microbes, T-phages as well as other phages act absolutely specific and selective against certain strains of germs.
However, phage therapy in Germany is subject to strict conditions, although in many cases it could be an excellent alternative to antibiotics. Although the problem of resistance formation is also present in T-phages, it can be remedied just as quickly by new cultivations of modified macrophages. Phage therapy has developed particularly in countries of the former USSR, mainly in Georgia. Some Western research groups are trying to breed phages that are also effective against multi-drug resistant bacteria.
T-phages are often cultured to produce enzymes in coliform bacteria to obtain larger quantities of enzymes needed for molecular biology purposes. These are enzymes such as T4 DNA ligase, T7 RNA polymerase and several others.
The ability of so-called temperate T-phages to incorporate their own DNA into the bacterial DNA (lysogeny), instead of unbridled replication of their own DNA, can also be used as a gene vector to perform targeted gene manipulation to target certain defective and disease-causing genes or gene fragments Replace genes or DNA pieces.
T-phages pose no direct danger to humans. Indirectly, T-phages could become a problem if they manage to attack and decimate unnoticed by the immune system coliform bacteria of the intestinal flora. T-phages and other phages are said to support the immune system to neutralize hard-to-fight and possibly multidrug-resistant bacteria.
Critics of phage therapy state that the therapy can only be used by physicians with appropriate training and that for a targeted application a bacterial culture must be created beforehand to be sure that they have chosen the "right" phage for the "right" bacterium. In contrast, broadband antibiotics would be readily available. The main argument against phage therapy, however, is feared by critics that the phage in its genetics could change so by mutations or uncontrollable gene exchange with the host bacterium, that the phage lose their phagocytic properties and mutate into an unmanageable pathogenic virus,
During the Cold War, Western medicine relied almost exclusively on antibiotics to ward off infectious agents, while Russia and the Soviet Union's member states, most notably Georgia, cultivated phage therapy. There is now evidence that both therapies have specific benefits and risks that need to be weighed before use.