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IB HL Biology

I really enjoyed HL biology. Definitely a subject worth taking HL as I learnt so much more about the human reproduction and the immune system. 

Some musing on Biology: 

Something that really appealed to me was the mutualism between the microbiota with our body. It was scary to learn that we have bacteria living inside our gut that not only helps us to absorb nutrients but also determines our mood each day. As for my curiosity, I wrote my Biology Extended Essay exploring the distribution of bacteria inside the digestive tract. I was also astonished to learn about bacteriophage and endophytes, and I can only conclude by noting that the wonders of nature never ceases to fascinate me!

Here is an article I wrote on bacteriophage that was published in the Young Global Scientists Journal:

YGS • Young Global Scientists 3rd Edition • January 2021

Bacteriophage as a Promising Alternative to Antibiotics


Surviving, reproducing and overcoming the imposing danger of medicine over time, bacteria have experienced a fortuitous evolution, an insurmountable climb by developing antibiotic resistance in the last era. The widespread misuse and overuse of antibiotics have created selective pressure for resistant strains, resulting in the survival and reproduction of more antibiotic-resistant bacteria. This has burgeoned the practice of bacteriophage therapy, an approach that uses viruses to treat bacterial infections.



Since the commercialization of penicillin in the mid-nineties, antibiotics have been used widely as both medicines for illness and feeds in the livestock industry to ensure the healthy growth of domesticated animals. After animals are fed antibiotics, selective pressure develops where susceptive bacteria are killed, leaving bacteria with resistant genes to proliferate. The first group of bacteria that survives is likely to confer tolerance to antibiotics from a gene mutation. For example, some mutations enable the bacteria to produce potent chemicals that deactivate antibiotics, while others eliminate the toll receptor, a distinguishing hallmark on bacteria that the antibiotic attacks. Over time, these domesticated animals retain strains of bacteria that are resistant to antibiotics. When undergoing conjugation, a bacterium transfers its genetic material, including resistant genes, onto another bacterium, forming a colony of antibiotic-resistant bacteria that flourishes in the intestinal organ of the animal. Similarly, the frequent use of antibiotics in the human population to treat innocuous diseases have also resulted in the production of resistant bacteria.

Amid growing concerns of a ‘return to the pre-antibiotic era’, the Centre for Disease Control (CDC) estimates that antibiotic-resistant infections result in 2 million illnesses and at least 23,000 deaths each year. According to the UK government’s 2016 review on Antimicrobial Resistance, an estimated 7,000,000 die each year globally from resistant infections with a projected cost of $100 trillion and a death toll of 10 million by 2050.

Bacteriophage therapy is largely considered as an alternative to antibiotics that has certain benefits such as low toxicity, biofilm penetration, and bacteria specificity.

Bacteriophage Treatment

A bacteriophage is a virus that infects a bacterium by inserting its genes inside it through the lytic and lysogenic cycle. It contains a head composed of nucleic acid covered by a protein layer and a tail as well as an empty core within the sheath, which can encode as few as four genes.

The lytic cycle is performed by virulent bacteriophages. It is a cytoplasmic viral replication process in which the bacteriophage injects its genetic material into the host cell, and uses the host bacterium genome to replicate phage genetic material to produce many more phages. Once the host cell is overloaded with bacteriophages, it ruptures from within, releasing the newly formed phages.

In the lysogenic cycle, a phage inserts its genetic material into the bacterium host without killing it. Once the bacterium host is colonized, the phage DNA is grafted onto the genetic material of the host, effectively creating an integrated chromosome that undergoes replication when the host bacterium divides to make more phage proteins.

Diagram acquired from blog “Fighting Fire with Fire: Killing bacteria with virus”

A case study by NCBI found “Recent investigations using animal models have explored phage treatment against a range of clinically significant pathogens. Oral administration of phage saved 66.7% of mice challenged with gut-derived sepsis due to P. aeruginosa from mortality compared to 0% in the control group. Intraperitoneal administration of a single phage strain was sufficient to rescue 100% of mice in bacteremia models using vancomycin-resistant E. faecium8, extended spectrum β-lactamase producing E. coli9, and imipenem-resistant P. aeruginosa10. Phage cocktails have also been used to treat antibiotic-resistant P. aeruginosa infections of the skin, lungs, and gastrointestinal tract in animal models11,12. Additional animal studies show similarly promising results for multidrug-resistant E. coli O25:H4-ST13113.” This data shows a promising result for bacteriophage applications.

In Connecticut, USA, an 80-year-old man suffering from life-threatening multi-drug-resistant bacterial infection in his heart was treated with bacteriophages. The patient had been infected with Pseudomonas aeruginosa, a type of bacteria which is common in nature and is often responsible for causing infections in hospital patients. The patient was treated with long-term antibiotics but to no avail. Running out of options, the patient was treated with OMKO1 bacteriophages that were studied intensively by researchers from Yale University. In January 2016, thousands of bacteriophages were injected into the man’s chest, and the patient was followed up to show no signs of bacterial infections.

Advantages of Bacteriophage Therapy over Antibiotics

Phages are specific to particular species of bacteria and therefore are unlikely to cause damage to beneficial microbes in our gut. Moreover, the way bacteriophages infect bacteria differs from antibiotics, indicating that specific antibiotic-resistant bacterial mechanisms do not translate into mechanisms of phage resistance, making phages a potential cure against superbugs.

Bacteriophage therapy is highly effective with planktonic bacteria, yet is limited in treating biofilm. A biofilm is a cluster of bacteria that live in association with the surface by an extracellular polymeric matrix. Biofilms typically derive a certain resistance to antibiotics from their having a physical barrier that makes inner cells less metabolically active and less affected by antibiotics. Bacteriophages are equipped with enzymes on the exterior of the capsid that degrade the extracellular polymeric substances and disperse bacterial biofilms, allowing them to access bacteria embedded within the matrix.

Limitations of bacteriophage

Despite the advantages of bacteriophages, there are abiding limitations. Firstly, phages are difficult to prepare cleanly. To produce phages, scientists must first grow a large number of bacteria that are not subjected to immune defence. Because phages can only infect particular species of antibiotics, they take a longer time to employ in treatment compared to antibiotics, as doctors need first to identify the bacterium that is causing the infection and then search for phages capable of killing it.

Secondly, phages are not widely used in the Western pharmaceutical industry. Few phage products have passed regulatory standards and phages are still known as ‘viruses’, which could be misinterpreted by the general public conjuring up the notions of dangerous viral pathogens that cause human diseases.


Antimicrobial resistance is increasing globally, and new treatments are urgently needed to meet this challenge. Relentless research on phages has led to an improved understanding of the safety and potential of bacteriophage therapy. However, data gaps on each and lack of standardization must be resolved before bacteriophage therapy can position itself as mainstream medicine.

Only by investing now to address Antibiotic Resistance can we ensure a future free from untreatable infections”. Anthony So, Professor of Health Practice at John Hopkins Bloomberg School of Public Health.

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