The Bacteriophages

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Also, this clinical trial is one of the few studies using i. The results were evaluated based on the following criteria: general condition of the patients, X-ray examination, reduction of purulence, and microbiological analysis of blood and sputum. No side effects were observed in any of the patients, including those who received phages intravenously.

Bacterial Host Specificity The bacterial host range of phage is generally narrower than that found in the antibiotics that have been selected for clinical applications. Advantages Over Antibiotics Phage therapy can be very effective in certain conditions and has some unique advantages over antibiotics.

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Antibiotics target both pathogenic microorganisms and normal microflora. This affects the microbial balance in the patient, which may lead to serious secondary infections.

High specificity may be considered to be a disadvantage of phages because the disease-causing bacterium must be identified before phage therapy can be successfully initiated. Antibiotics have a higher probability of being effective than phages when the identity of the etiologic agent has not been determined. Replicate at the site of infection and are thus available where they are most needed They are metabolized and eliminated from the body and do not necessarily concentrate at the site of infection. The "exponential growth" of phages at the site of infection may require less frequent phage administration in order to achieve the optimal therapeutic effect.

No serious side effects have been described. Multiple side effects, including intestinal disorders, allergies, and secondary infections e. Example structure of a bacteriophage. In order to reproduce, phage must first enter the host cell. They bind to specific receptors on the bacterial cell surface with their tail fibers adsorption and create a hole, a process which, along with attachment, is coordinated by the base plate 3.

A rigid tube is propelled out of the sheath, puncturing a hole in the bacterial cell membrane through which they inject their genetic material DNA or RNA, double or single stranded. Alternatively, they may enter a dormant state, known as the lysogenic cycle, within the host cell if conditions are favorable. In the lytic cycle Figure 2 , sometimes referred to as virulent infection, the infecting phage ultimately kill the host cell to produce many of their own progeny.

Immediately following injection into the host cell, the phage genome synthesizes early proteins that break down the host DNA, allowing the phage to take control of the cellular machinery. The phage then uses the host cell to synthesize the remaining proteins required to build new phage particles. The heads and sheaths are assembled separately, the new genetic material packed into the head and new daughter phage particles constructed.

During this process, the host cells gradually become weakened by phage enzymes and eventually burst, releasing on average new phage progeny into the surrounding environment. Figure 2.

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Depiction of the stages of the bacteriophage lytic cycle. Watch the lytic cycle in action here.

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The lysogenic cycle Figure 3 , sometimes referred to as temperate or non-virulent infection, does not kill the host cell, instead using it as a refuge where it exists in a dormant state. Following the injection of the phage DNA into the host cell, it integrates itself into the host genome, with the help of phage-encoded integrases, where it is then termed a prophage.

The prophage genome is then replicated passively along with the host genome as the host cell divides for as long as it remains there and does not form the proteins required to produce progeny. As the phage genome is generally comparatively small, the bacterial hosts are normally relatively unharmed by this process. Figure 3. Depiction of the stages of the bacteriophage lysogenic cycle. If a bacterium containing prophage is exposed to stressors, such as UV light, low nutrient conditions, or chemicals like mitomycin C, prophage may spontaneously extract themselves from the host genome and enter the lytic cycle in a process called induction.

This process, however, is not perfect and prophage may sometimes leave portions of their DNA behind or take portions of host DNA with them when they re-circularize. If they then infect a new host cell, they may transport bacterial genes from one strain to another in a process called transduction.

This is one method by which antibiotic resistance genes, toxin and superantigen-encoding genes and other virulence traits may spread through a bacterial population. Recent work has shown that transition between lytic and lysogenic infection is also dependent on the abundance of phage in an area as they are able to produce and sense small peptides in a process akin to quorum sensing 4.

These spacer sequences were found to have homology to viral and plasmid DNA, including phage. In response to phage invasion, the CRISPR sequences are transcribed and, in partnership with Cas proteins, target and destroy the phage sequences that are homologous to the spacers sequences.

The Bacteriophages

A biochemist with a love of microbiology, the Lab Rat enjoys exploring, reading about and writing about bacteria. Having finally managed to tear herself away from university, she now works for a small company in Cambridge where she turns data into manageable words and awesome graphs. You have free article s left. Already a subscriber? Sign in.

But why do phagebiotics matter now?

A bacteriophage also known informally as a phage is a virus that infects and replicates within bacteria and archaea. The term was derived from "bacteria" and . Control Mechanisms in dsDNA Bacteriophage Assembly. Sherwood Single- Stranded RNA Bacteriophages Phages with Protein Attached to the DNA Ends.

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