{"id":123,"date":"2018-04-13T10:35:56","date_gmt":"2018-04-13T10:35:56","guid":{"rendered":"https:\/\/www.sciencesg.com\/mistrologics\/?p=123"},"modified":"2018-04-13T17:06:48","modified_gmt":"2018-04-13T17:06:48","slug":"bacteriophage-therapy-drug-resistance","status":"publish","type":"post","link":"https:\/\/www.sciencesg.com\/mistrologics\/bacteriophage-therapy-drug-resistance\/","title":{"rendered":"Potential of Bacteriophage Therapy against Antibiotic Resistance"},"content":{"rendered":"

Antibiotic Resistance is a critical problem<\/h2>\n

The emergence of Multiple Drug Resistant (MDR) pathogenic bacteria has lessened the effectiveness of antibiotic drugs designed to cure or prevent infections. The issue is so critical that United Nations recently declared it a fundamental threat<\/a> to global health. Unless concerted global actions are initiated, we will head for the pre-antibiotic era, when common bacterial infections and minor injuries can lead to serious disability or even death. Among the alternative therapeutic techniques, Bacteriophage Therapy has the best potential to act against the threat of MDR bacteria with much lower side effects.<\/p>\n

It is to be noted that some bacteria are naturally resistant to certain antibiotics and some can develop resistance by a spontaneous genetic mutation or acquiring antibiotic resistance genes from other bacteria. Antibiotics kill or inhibit the non-resistant bacteria and lets the resistant bacterial strains (superbug) to survive and multiply.<\/p>\n

\"Superbug<\/p>\n

Pathogenic Bacteria frequently live in biofilms<\/h3>\n

In many different natural and man-made environments, including dental plaques, water pipes etc. pathogenic bacteria is found to reside in biofilms<\/a>, which are surface-attached aggregates embedded in a matrix of extracellular polymeric substance.<\/p>\n

The biofilm matrix comprises of polysaccharides, structural proteins, enzymes, DNA, lipids, and water which protects its inhabitants from environmental challenges thereby allowing long-term colonization. The extracellular polymers or modifying enzymes also inactivate the antibiotics, and furthermore, the localized gradients in biofilm matrix provide zones where the bacterial cells can survive and initiate relapse of the disease.<\/p>\n

The cells in the biofilm are closely spaced facilitating communication by the process of quorum sensing<\/a>, which along with an increased level of mutations is responsible for the growth of the biofilm. It is found to be most likely that the bacteria in biofilms use conjugation mechanism to transfer genes within or between populations and thus develop further antibiotic resistance.<\/p>\n

As a consequence, biofilm-specific resistance is usually 1,000-fold higher than antibiotic resistance of planktonic bacteria.<\/p>\n

\"Biofilm
\n<\/p>\n

Bacteriophage Therapy has a contentious history<\/h2>\n

Bacteriophages are bacteria-specific viruses, which play a crucial role in regulating bacterial populations in nature. The use of bacteriophage to treat bacterial infections started long before the discovery of penicillin, the first true antibiotic.<\/p>\n

It goes without saying that at the time of the discovery of bacteriophage therapy even the existence of bacteriophage was a topic of dispute until after the evolution of electronic microscopy.<\/p>\n

From that time on, a number of logistical and technical obstacles in its implementation, along with the inconsistent success stories and the successful advancement of antibiotic treatment have led to its abandonment in the United States and Western Europe. Bacteriophage Therapy continued to develop and refined in the former USSR and Poland. Ultimately, it took the severities of antibiotic resistance to force the western world to look back at the bacteriophage therapy.<\/p>\n

Biology and Lifecycle of Bacteriophage<\/h2>\n

Bacteriophages consist of DNA or RNA encapsulated within a protein capsid. Being parasitic in nature, these are dependent on a bacterial host for survival and reproduction.<\/p>\n

The first step of the bacteriophage-bacteria interaction is the attachment of the bacteriophage to the specific receptors of the bacterial cell wall.<\/p>\n

Upon attaching itself to the specific receptors, the Bacteriophages induce a pore in the bacterial cell wall, and inject their genome into the host cell, leaving its viral capsid outside of the bacteria.<\/p>\n

\"Bacteriophage
Bacteriophage injecting its genome into bacteria<\/strong><\/figcaption><\/figure>\n

Thereafter either lytic or lysogenic pathway of development takes place depending on the nature of the bacteriophage, state of the bacteria host, nutritive components surrounding the host etc. It is to be noted that Virulent Bacteriophages can follow only lytic pathway, whereas Temperate Bacteriophages can choose between the two pathways.<\/p>\n

In the lytic pathway, the bio-synthetic machinery of the host bacteria is hijacked to reproduce viral genome and proteins. This is followed by assembling and packing to form the progeny virions. The late enzymes holin and endolysin are then synthesized to assist in cell lysis and liberation of the virions to the extracellular environment to infect other bacteria.<\/p>\n

In the lysogenic pathway, the genome of the bacteriophage integrates into the host bacteria by physical incorporation into the bacterial chromosome in the form of an endogenous prophage. The prophage remains dormant for many host generations until the lytic cycle is induced and is replicated as part of the bacterial chromosome. After induction the prophage starts producing viral proteins and copies of viral genome using the resources and bio-synthetic machinery of the bacteria. This process leads to the formation of progeny virus particles, and after completion of the cycle, these virions are released during host cell lysis.<\/p>\n

Temperate Bacteriophages follow lysogenic pathway when the host bacteria offer poor growth conditions, because then the lytic pathway would produce very low number of progeny virions.<\/p>\n

<\/p>\n

Benefits and Constraints of Bacteriophage Therapy<\/h2>\n

Bacteriophages are natural antibacterials, and thus offer various superiority compared to Antibiotics. However, they are not still the \u201cmagic bullet\u201d to treat any type of infection.<\/p>\n

Bacterial Host Specificity<\/h4>\n

Bacteriophage Therapy has a very narrow antibacterial spectrum with its effect limited to just a single species of bacteria or in some cases a single strain within a species. As a result it does not damage health-protecting normal flora bacteria, or interfere with mammalian cells. Bacteriophages also penetrate deeper as long as the infection is present, and stop reproducing once target bacteria are destroyed.<\/p>\n

By contrast, most antibiotics have broader spectra of activity, and thus frequently trigger secondary infection caused by an opportunistic pathogen. Also, antibiotics continue to act even after the infection is cured until excretion and\/or degradation.<\/p>\n

The high specificity of bacteriophage therapy is a liability too. To define a specific bacteriophage solution, the clinical sample needs to be isolated and cultured for identifying the pathogen. This is a time-consuming process in resource-limited healthcare setup.<\/p>\n

This situation can be overcome by using Bacteriophage Cocktails by mixing a selection of potent bacteriophages, resulting in a broader spectrum of activity. Such cocktails are also useful in treating infections caused by genetically different strains of bacteria.<\/p>\n

Notwithstanding, a large collection of well-characterized Bacteriophages for a broad range of pathogens are being developed continually, and also methods are being refined to rapidly determine the type of bacteriophage strains effective for any given infection. It is also necessary to sequence the gene of each type of Bacteriophage, as some of these genes might have the potential to promote deleterious side effects.<\/p>\n

Nevertheless, the therapeutic use of Bacteriophages is likely to lag behind as new pathogenic bacteria evolve.<\/p>\n

\"Bacteriophages
Bacteriophages attached to a bacterial cell<\/strong><\/figcaption><\/figure>\n

Large size of bacteriophage limits its Therapeutic use<\/h4>\n

The large size of Bacteriophage, along with the inability to prepare highly concentrated solution means that the number of Bacteriophages per dosage is much smaller compared to antibiotics #1<\/sup>. Moreover, the large size of bacteriophage is also responsible for its slow diffusion. So, bacteriophage needs to be applied at the very site of infection where the concentration of bacteria is highest.<\/p>\n

Regardless, it is worth mentioning that virulent Bacteriophages rapidly increase in number through replication and thereby self-optimize the dosage, although, these depend on relatively high bacterial densities. Bacteriophage therapy is therefore most useful in treating acute infections.<\/p>\n

Bacteriophage Therapy is limited to Virulent Bacteriophages<\/h4>\n

Virulent Bacteriophages are useful for therapeutic use because these in most cases lyse any bacteria within the hour. The rate of adsorption on the bacterial surface, latent period and burst size of the bacteriophage contribute towards its efficacy #2<\/sup>.<\/p>\n

By contrast, bacteriophages following lysogenic pathway are not suitable to treat acute infections due to the delayed induction of the lytic cycle. Moreover, this kind of Bacteriophages can potentially transduce antibiotic resistance genes, leading to the formation of a new microbe or even more resistant bacteria, and also encode bacterial virulence factors, including bacterial toxins.<\/p>\n

Despite such benefits, the fact that Virulent Bacteriophages induce the lysis of bacteria, liberating endotoxin and inflammatory mediator, may account for several side effects on the host. For this reason, lysis-deficient bacteriophages and engineered phagemids, that kills the target bacterial cell but is incapable of host cell lysis, are being considered as the better alternatives.<\/p>\n

\n#1<\/strong>: Bacteriophage solution becomes too viscous at higher concentrations.<\/em><\/sup>
\n#2<\/strong>: Latent Period is the time required for host cell lysis after introduction of bacteriophages genome. Burst Size is the number of viral progeny produced per infected bacterium.<\/em><\/sup><\/p>\n

<\/p>\n

Immunological Response<\/h4>\n

Since they are viruses, bacteriophages can trigger immunological response, and therefore eliminated from the systemic circulation by reticulo-endothelial system clearance, or inactivated by the adaptive immune defense mechanisms, causing reduced efficacy. However, such immunological response depends on the location of the infection and the way in which bacteriophages are added.<\/p>\n

Since, bacteriophages are naturally present in what we eat and drink, its consumption has not led to any immunological complications. However, bloodstream and other internal organs are not their natural environments, and thus intravenous administration of bacteriophages has been shown to activate both the innate and the adaptive immune system. Nevertheless, all bacteriophages are different, and it is thus necessary to test the immunological response of each single bacteriophages.<\/p>\n

Bacteriophage Resistance<\/h4>\n

Bacterial host also develops resistance to a bacteriophage, just as to an antibiotic, resulting in decreased efficacy of bacteriophages. However, compared with antibiotics, bacteriophages exhibit a much narrower potential for inducing resistance because of their high bacterial host specificity.<\/p>\n

Various mechanisms may be involved in the process of developing resistance.<\/p>\n