{"id":148,"date":"2025-12-03T13:24:00","date_gmt":"2025-12-03T07:54:00","guid":{"rendered":"https:\/\/www.najao.com\/learn\/?p=148"},"modified":"2026-01-26T02:22:20","modified_gmt":"2026-01-25T20:52:20","slug":"phage-therapy","status":"publish","type":"post","link":"https:\/\/www.najao.com\/learn\/phage-therapy\/","title":{"rendered":"Phage Therapy: A Resurgent Solution to the Antibiotic Resistance Crisis"},"content":{"rendered":"\n

Our world is facing an unprecedented crisis of antimicrobial resistance<\/a> (AMR) in which bacteria and other microbes are developing resistance to medications like antibiotics that were once effective against them. As a result of AMR, even common infections are developing the potential to become deadly, leading the WHO to declare AMR a \u201csilent pandemic<\/a>,\u201d and consider it one of the top ten global public health threats to humanity in the 21st century.<\/p>\n\n\n\n

A number of promising strategies are now being employed to counter the threat of AMR, and among them phage therapy is noteworthy1<\/sup><\/strong>. This promising, re-emerging approach utilizes bacteriophages\u2014viruses that exclusively infect and kill bacteria. This beneficial use of viruses is similar to that of oncolytic viruses<\/a>, which are used to target and destroy cancer cells.<\/p>\n\n\n\n

Phage therapy isn\u2019t new; its history dates back to the early 20th<\/sup> century with the independent discovery of bacteriophages by Frederick Twort and F\u00e9lix d’H\u00e9relle2<\/sup><\/strong>. Before antibiotics started to become widely available in the West, phage therapy was commonly used in Eastern Europe, notably at the Eliava Institute in Georgia<\/a>. Before the emergence of the AMR crisis, Western medicine largely abandoned phages, but now phage therapy is gaining a renewed and fervent interest as a highly specific, effective, and environmentally friendly approach to combat antibiotic-resistant bacteria3<\/sup><\/strong>.<\/p>\n\n\n\n

Understanding bacteriophages<\/h2>\n\n\n\n

Bacteriophages, often simply called phages, are viruses that exclusively infect bacteria and are found wherever bacteria thrive\u2014in soil, water, sewage, and even within the human body4<\/sup><\/strong>. The fundamental structure of phages consists of genetic material (either DNA or RNA) encased within a protective protein shell called a capsid.<\/p>\n\n\n\n

Phage life cycles<\/h3>\n\n\n\n

Phages primarily operate through two distinct life cycles: the lytic cycle and the lysogenic cycle5<\/sup><\/strong>.<\/p>\n\n\n\n

Lytic cycle (virulent phages)<\/h4>\n\n\n\n

This cycle describes how virulent phages kill their bacterial hosts. First, the phage binds specifically to unique receptor sites on the surface of a target bacterium, and then injects its genetic material into the bacterial cell, leaving its capsid outside. The genetic material of the phase then hijacks the cellular machinery of the bacterium and redirects it to synthesize phage components like proteins and nucleic acids. After the synthesis, the phage components self-assemble to form complete progeny phage particles. Following this, the phage produces enzymes, such as lysins and holins, that trigger the lysis of the bacterium by degrading the bacterial cell wall from within. Consequently, hundreds of new, infectious phage particles get released, ready to infect other bacteria.<\/p>\n\n\n\n

Lysogenic cycle (temperate phages)<\/h4>\n\n\n\n

In this cycle, the temperate phage integrates its DNA into the bacterial chromosome, forming a prophage that then replicates along with the bacterial DNA during normal cell division, lying dormant. Under certain stress conditions, like UV radiation, the prophage can excise itself from the bacterial chromosome and enter the lytic cycle.<\/p>\n\n\n\n

Virulent phages that undergo the lytic cycle are crucial for therapeutic applications as they kill the target bacteria, a primary goal of phage therapy. Temperate phages are generally avoided as they do not immediately kill bacteria, and because they sometimes carry and transfer virulence factors or antibiotic resistance genes, worsening an infection6<\/sup><\/strong>.<\/p>\n\n\n\n

Phage specificity<\/h3>\n\n\n\n

Phages typically recognize and infect only very specific bacterial strains, or sometimes a narrow range of strains within a species7<\/sup><\/strong>. This gives phage therapy a significant advantage over broad-spectrum antibiotics, as it can eliminate pathogenic bacteria without disrupting the beneficial bacteria that make up the human microbiome. On the flip side, such specificity requires precise identification of the infecting bacterial strain, necessitating rapid diagnostic capabilities8<\/sup><\/strong>. It also requires the availability of potentially large, well-characterized phage libraries to choose a specific phage (or mixture of phages) that can effectively lyse the strain, which is crucial for the success of phage therapy9<\/sup><\/strong>.<\/p>\n\n\n\n

Mechanisms of action in phage therapy<\/h2>\n\n\n\n

Targeted bacterial lysis<\/h3>\n\n\n\n

The primary and most direct mechanism is the highly targeted bacterial lysis that occurs during the lytic cycle. In addition, phages self-amplify in situ<\/em> as long as their target bacteria are present, thereby enabling sustained therapeutic levels, unlike antibiotics that are consumed or metabolized10<\/sup><\/strong>.<\/p>\n\n\n\n

Biofilm penetration and disruption<\/h3>\n\n\n\n

Biofilms<\/a>, which encase the bacterial community in a protective extracellular matrix, are notoriously resistant to both antibiotics and host immune defenses. Many phages can penetrate such matrices, either through passive diffusion, active motility, or by producing enzymatic depolymerases that degrade the matrix components11<\/sup><\/strong>. Once inside, phages can infect and lyse bacteria within the biofilm. In cases where phages disrupt the biofilm structure, the remaining bacteria also get exposed to host immune cells as well as co-administered antibiotics12,13<\/sup><\/strong>.<\/p>\n\n\n\n

Immune system modulation<\/h3>\n\n\n\n

Phages don’t directly target host cells, but their interaction with bacteria can indirectly influence the host’s immune system14<\/sup><\/strong>.<\/p>\n\n\n\n