Fighting micro monsters

An overview of what bacteria are, and how antibiotics can prevent them from causing diseases

Chances are, you or someone you know has been prescribed a course of antibiotics this past year alone. Whether it’s to fight off pneumonia or another particularly nasty bacterial infection, or as a precaution before surgery, antibiotics are a common part of the healthcare process. But what are they exactly, and how do they work?

Put simply, anything that prevents the growth of bacteria, or kills it, can be called an antibiotic. The word itself means “anti-life”, derived from the Greek word “bios” which means life.

While modern antibiotics are produced in laboratories, they are usually derived from compounds and substances found in nature, such as mould, fungi, and yes, even bacteria.

Vancomycin, an antibiotic often used to treat colitis and severe skin infections, was first discovered in a soil-based bacteria from the Borneo region. In fact, to this day, some commercial antibiotics are made from bacteria grown in large fermentation vats. Some are synthetically produced, or modified chemically, to reduce potential side-effects or improve their efficacy.

Of course, bacteria are not the only microorganisms that can be harmful to humans; viruses and fungi can cause potentially dangerous infections that antibiotics would be rather useless at fighting off. This is why the current clinical practice is not to automatically prescribe antibiotics for colds and the flu, which tend to be either caused by viruses or can be easily fought off by the body.

What are bacteria?

The next sentence may concern you if you are a germophobe: chances are, at this very moment, you have the company of millions of bacteria. Whether they are in your surrounding environment, or even in your own body, these ancient and tiny critters are going about their simple prerogative to exist.

Bacteria are single-cell microorganisms; unlike most other living things, the lone bacterium is entirely self-sufficient. While bacteria generally live in large numbers, they are not dependent on each other for survival.

The structure of a bacterium can be simplified into three components. At its heart (or rather, insides) is the cytoplasm, a fluid containing the bacterium’s cell structures, nutrients and enzymes. This is where the micro-organism carries out the functions it needs to live. Surrounding the cytoplasm is a membrane, which regulates the water and salts in the cell. The cell wall acts as a final barrier between the bacterium and the outside world.

Considering that they have been found in the most inhospitable of environments, from the depths of the ocean to the insides of volcanos, it may be no surprise that the average person has some trillions of bacteria in their bodies. In fact, bacteria outnumber human cells by 10 to one, according to the United States’ Human Microbiome Project. If it is any consolation, scientists also say that these creatures only make up about 1% to 3% of the body’s mass due their small size. Additionally, many of these bacteria are beneficial to our health — those present in the gut for instance, help the digestive process and even produce vitamins like B and K.

Only 1% of bacteria are identified as pathogens — microorganisms which can cause disease — but these include nasty ailments such as cholera, typhoid and gonorrhoea. While many bacteria feed off dead organic material or produce their own food, some can wreak havoc by attacking living tissue. Others can cause harm to their hosts just by excreting toxins.

How do antibiotics work?

Antibiotics work in a number of ways to either kill bacteria, or prevent it from growing or replicating to allow the body some time to fight off the infection. What makes antibiotics particularly useful is that they selectively attack bacteria without causing any harm to the cells of a patient.

Bacteria need particularly strong cell walls to be able to survive their exposure to the environment. Some antibiotics, such as penicillin, block the production of a special type of molecule that enables the bacterium to build this outer wall. This in turn causes a weaker cell wall, which can easily burst and kill the bacterium.

Other antibiotics meanwhile, attack the cell membrane of the bacterium. This membrane regulates the water and salts within the bacterium; if it breaks, the bacterium will die from having its contents spill out.

Like most living organisms, the building blocks of a bacterium is its DNA. In order for the cell to reproduce, it needs to replicate its DNA — basically copying all its genetic material into a new cell. Some antibiotics are able to prevent DNA replication in bacteria in different ways. Ciprofloxacin, an antibiotic that has proven useful in treating the anthrax bacteria, targets a type of enzyme in bacteria that manages its DNA replication — without affecting the same enzyme in humans.

Some antibiotics work by starving bacteria from the nutrients they need to live and grow. While human cells can easily absorb folic acid, an essential component for cell growth, bacteria cannot take in the vitamin and need to make their own. Drugs such as sulphonamide antibiotics, prevent bacteria from doing so; without the required folic acid, the bacteria is then unable to grow.

Along with vitamins, proteins are equally crucial for cells — including bacteria — to survive. Antibiotics such as tetracycline, commonly used to fight acne and chest infections, stops protein synthesis in bacteria. This makes them unable to build proteins, and gradually die out.

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