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Use of Antibiotics

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Use of Antibiotics

Antibiotics are antimicrobial chemicals produced in nature by bacteria and fungi. These chemicals help the producing organism by killing or inhibiting its microbial competition to limited resources like water or food, especially in environments where these resources are less available. These chemicals have had an enormous impact on therapeutics over the past decades because of their proficiency in exclusively killing bacterial cells. While antibiotics in medicine are well known, antibiotics are used for a wide array of other purposes.

The uses of antibiotics

As mentioned, the most widely known use of antibiotics is in therapeutics to treat medical conditions caused by bacteria. However, this is not the only use. Antibiotics are used in microbial culture, farming, food preparation, building, domestic products and several other areas.

Antibiotic use in medicine

Antibiotics are used in medicine to treat bacterial infections; they function by either halting bacterial growth or outright killing the bacteria. The former group are termed bacteriostatic antibiotics and the latter bactericidal antibiotics.

The following table provides an overview of the main antibiotic classes used in therapeutics.

Antibiotics are used as antibacterial drugs extensively to treat bacterial infectious diseases by exclusively targeting the bacterial cell and not the host organism. Antibiotics can only be used to target bacteria and not viruses! Antivirals are required to treat viral infections and not antibiotics.

Bacteriostatic Antibiotic Classes:
Bactericidal Antibiotic Classes:
Macrolides
Penicillins
Sulfonamides
Cephalosporins
Tetracyclines
Fluoroquinolones
Aminoglycosides

Penicillin (part of the penicillins class) is perhaps one of the most famous antibiotics and the first to be discovered. Penicillin was discovered in 1928 by Alexander Fleming in London. However, it took several years until its full potential to treat infectious diseases was realised, and it became widely available in the 1940s. Penicillin started a new age in modern therapeutic medicine!

Which antibiotic is used depends on several factors, including the infection's location, causative bacteria, bacterial resistances, patient allergies, and the infection's severity. The delivery method also varies. Some antibiotics are taken orally, whereas others are injected or inhaled. Which route is used depends on the location of the infection, its severity, and the drug being used.

Incorrect medical use of antibiotics is one of the major sources of developing antibiotic resistance. Antibiotic resistance occurs when antibiotics are exposed to selection pressure, in this case, insufficient antibiotics to kill or prevent the growth and division of an entire population of bacteria. This often occurs due to using antibiotics to treat incorrect conditions, such as viruses, or because people don't take the full course of antibiotics prescribed to them. It may also occur randomly or when antibiotics are being used correctly, but this is much more limited. Using antibiotics appropriately to maintain their efficacy is termed antibiotic stewardship.

Read our article on Antibiotic Resistant Bacteria to learn about how antibiotic resistance is a serious challenge in therapeutics today!

The uses of antibiotics in agriculture

Antibiotics are used and abused in many areas of farming, some for good reason and others less so. Around 66% of antibiotics manufactured yearly are used in animals. Antibiotic use in farming is another major source of antibiotic resistance.

Antibiotics in animal farming

Antibiotics are used in animal farming for the legitimate use of treating animal infections. In this case, antibiotics are used similarly to human medicine. The other major use of antibiotics in animal farming is as growth promoters. In this case, antibiotics are introduced at sub-therapeutic doses (lower than the medical dose) through the animals' food and water. This causes them to grow quicker. The exact mechanisms behind this are not precisely known; however, it is believed to be a result of either the killing of gastrointestinal bacteria, which consume nutrients that could otherwise be used for growth, or the prevention of infections that cause limited growth.

The use of antibiotics as growth promoters is illegal within the European Union (EU); however, up until 2017, it was common practice in the USA and is still ongoing elsewhere. Antibiotic growth promoters help farmers by increasing the conversion rate of feed to animal products, meaning they get more products for their investment in feed. However, as the exposure is sub-therapeutic, it creates a perfect environment for developing antimicrobial resistance by presenting a consistent selection pressure to bacteria within the animals. This is especially concerning as many microbes present in animals are also human pathogens, meaning resistance that arises in animals can easily transfer to human pathogens either directly or through the transfer of genetic material.

Antibiotics are also used prophylactically to prevent infection, operating on the principle that animals can't get sick if the bacteria that cause the infections are killed before they can cause an infection. This is used when animals are raised in tightly packed, less clean conditions.

Prophylactics are medicines given to prevent rather than treat disease. Medicine provided in this manner is said to be given prophylactically. An example of a prophylactic is the pre-exposure medicine given to those at risk of contracting HIV to prevent infection.

Antibiotics in horticulture

Antibiotics are used within horticulture for the treatment of many plant diseases. They are generally applied prophylactically via sprays, as application after infection is generally not effective. Due to the introduction of antibiotics to the environment, this treatment presents another avenue for developing antimicrobial resistance. This release of antibiotics into the environment occurs due to overspray not landing on the plants or rain washing the drugs into the surrounding environment.

Antibiotics in fish farming

Fish farming, also known as aquaculture, is another area where antibiotics are generally administered as a preventative, prophylactic measure instead of a treatment. While aquaculture is often used to refer to fish farming, it describes the farming of any aquatic organism in salt, brackish or freshwater. Similar to antibiotic use in animal farming, this preventative measure protects profits by minimising sickness in farmed organisms. The chances of disease arising are exacerbated by the incredibly high stocking levels usually present in aquaculture. The density of the organisms plus the high levels of waste generated by them means an infection is highly likely to occur. When that is the case, the disease can spread rapidly through the population.

Like with all other non-medical uses of antibiotics, this use of antibiotics often leads to the release of the drugs into the surrounding environment. The organisms may be raised out of natural bodies of water in artificial habitats. Still, the likelihood of antibiotic release into the surrounding environment in these setups depends on the method used.

Tanks present the lowest risk of antibiotic release, as the water is entirely isolated from the environment, and with appropriate treatment, antibiotics can be prevented from entering the environment. This may be extended to aquaponics, which flows the water through plant beds to use the organism's waste to fertilise land plants. Ponds present the next best option, as the water may still be processed to prevent antibiotic release; however, the in-ground nature increases the likelihood of accidental release. Raceways are a semi-artificial, semi-natural method; they utilise artificial channels for water diverted from a natural source to run through. This water may then be sent back into the water flow or treated. If the water is sent straight back into the source, any antimicrobials are also released into it.

An alternative to artificial environments is enclosing natural water areas, either in shallow, near-shore waters or pens in deep, open water. These both present the largest risk of antibiotics being released into the surrounding ecosystem. The water is simply part of the natural body, separated only by the mechanism used to contain the farmed organisms.

Antibiotics in insect farming

Like animals, insects are susceptible to infection by bacterial pathogens. While a variety of insects are cultivated for the production of human foodstuffs, the most common globally is the honey bee. So these present the main use of antibiotics in insect farming. Insects are also farmed for non-human foodstuffs, including for use as animal feed, which may lead to antibiotics being inadvertently passed on to other areas.

While most beekeepers apply antibiotics at therapeutic levels, some also utilise them at sub-therapeutic levels to have similar effects on product output as antibiotics used as growth promoters in animals. As with other negligent uses of antibiotics, this use can present a selection pressure that encourages the development of antimicrobial resistance. Another significant issue is that many insects exhibit limited metabolism of antibiotics, which means a significant proportion of the dose can be passed on, either through the consumption of the insects or their products, such as honey.

Uses of antibiotics in shipping

Antibiotics, mainly tetracyclines, are often included in paint used for ships! Organisms such as barnacles or algae can attach to vessels by forming a bacterial biofilm. The added mass and friction due to the presence of this organism slows the ship and increases the amount of fuel used. The attachment of these organisms is known as biofouling, and so the paints used to prevent them are known as anti-fouling paints.

Biofilms are a colony of microorganisms held together by secreted polymers comprised of many biological molecules. This allows them to share nutrients while being protected from environmental stressors.

Biofouling occurs in several stages, gradually increasing in size of the organism. First organic polymers bind to the surface, providing a substrate for bacteria and diatoms to colonise, forming the previously mentioned biofilm. The biofilm then allows algae and protozoa to attach, encouraging larger organisms such as barnacles to colonise the surface. These large organisms have the largest impact on speed and fuel economy. The collective organisms on the surface are known as a fouling community. By adding antibiotics to the paint, the bacteria that form the biofilm may be killed, so the fouling community's formation halted or slowed!

The uses of antibiotics in microbial culture

Bacterial contamination presents a significant threat to the success of microbial cultures. Generally, the end goal of culturing microorganisms is to have a pure culture of a single microorganism, either for the microorganism itself or one of its products. Bacterial contamination can compete with other microorganisms, preventing or limiting their growth or contaminating the end product, rendering it unusable, or increasing the complexity and cost of purification. The use of antibiotics in microbial cultures may help prevent this.

Microbial cultures are a foundational research methodology in microbiology. They're used to grow microbial organisms in controlled laboratory conditions using a culture medium.

Antibiotics are also used when modifying microorganisms. When inserting genetic material via vectors into a bacteria, an antibiotic that the target bacteria is susceptible to is used to select for bacteria that have taken up the genetic material. This is done by including a resistance gene for that antibiotic within the vector, meaning that bacteria containing the vector become resistant. The antibiotic kills any that did not take it up. This allows the microbial culture to have only successfully modified bacteria.

Vectors are molecular biology research tools used to transfer foreign genetic material into cells.

Pros of using antibiotics

Both the medical and non-medical applications of antibiotics present several benefits.

  • Their use as a growth promoter increases the efficiency and profitability of animal farming.
  • Prophylactic administration prevents disease in a variety of organisms and farming systems.
  • The use of antibiotics in medicine revolutionised treatments and means that bacterial infections that were once incredibly dangerous are now mere inconveniences.
  • Their use in shipping lowers cost and increases efficiency, thereby also decreasing emissions from shipping.
  • Finally, their use in microbial culture allows for more efficient culture, preventing contamination and selecting successfully modified organisms.

Consequences of antibiotic use

Antibiotic use can lead to the development of resistances, where the drug's efficacy is lost. As previously discussed, this occurs due to incorrect doses, where a selection pressure is created, and naturally occurring mutations that convey resistance are selected. Their unsupervised use in agriculture and other areas increases the likelihood of incorrect doses being used, which significantly increases the likelihood of resistance occurring when antibiotics are used for this purpose compared to medicine.

Another significant consequence of non-medical antibiotic use is the release of antibiotics into the environment through agricultural runoff or other means. This is termed antibiotic pollution and may significantly alter the natural bacterial population in an area and increase the likelihood of resistance developing. Antibiotic use in the food chain can also lead to accidental exposure of humans to antibiotics through the contamination of foodstuffs. This is exacerbated by bioaccumulation, a phenomenon where a substance accumulates in an organism from its surrounding environment, food and water.

Use of Antibiotics - Key takeaways

  • Antibiotics are used in medicine, agriculture, shipping and microbial culture, among other areas. Antibiotics may stop bacterial growth (bacteriostatic) or kill bacteria (bactericidal).
  • Antibiotic resistance stems from improper use of antibiotics, creating a selection pressure that selects for mutations conveying resistance.
  • Antibiotics may be used in animal farming to promote growth. They are also used prophylactically to prevent disease before an outbreak occurs.
  • Horticulture uses antibiotics prophylactically to prevent infection. Aquaculture uses antibiotics to limit disease. Insect farming uses antibiotics to prevent or treat disease.
  • Antibiotic pollution alters the ecosystem of an area and increases the likelihood of antimicrobial resistance occurring.

Frequently Asked Questions about Use of Antibiotics

Antibiotics are used for controlling the impact of bacteria by either killing them or halting their growth. 

Around 66% of annual global antibiotic production is used in animals instead of human medicine. 

The main use of antibiotics is to control disease, however they may also be used to prevent contamination in microbial culture or to increase the growth rate of animals. 

Antibiotics are added to animal feed and water to prophylactically prevent disease due to the cramped confines and poor sanitation often present in farming. They also may promote more rapid growth via poorly understood mechanisms. This means a higher feed conversion rate and  more profit for the farmer. 

Antibiotics are used in agriculture to prevent disease through prophylaxis, cure disease or promote growth in animals. 

Final Use of Antibiotics Quiz

Question

What type of antibiotic kills bacteria?

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Answer

Bactericidal Antibiotics

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Question

What type of antibiotic halts bacterial growth and reproduction?

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Answer

Bacteriostatic Antibiotics

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Question

What modes of delivery are usually used with antibiotics?

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Answer

Ingestion, inhalation and injection. 

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Question

What is the term used to describe ensuring antibiotics are used sensibly, in a manner which preserves their efficacy for as long as possible?

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Answer

Antibiotic Stewardship 

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Question

Other than to treat or prevent disease, why are antibiotics used in animal farming?

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Answer

Antibiotics are used as growth promoters in animal farming to increase the growth rate and feed conversion efficiency of livestock. 


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Question

How does antimicrobial resistance occur?

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Answer

Through natural mutations being selected for by sub-therapeutic levels of antibiotics. 

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Question

Why does agriculture use antibiotics prophylactically?

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Answer

To prevent disease, the likelihood of which is increased due to close quarters and often less than sanitary conditions. 

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Question

How are antibiotics applied in horticulture?

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Answer

Via sprays. 


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Question

Are antibiotics used to treat diseases or as a prophylactic measure in horticulture?

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Answer

They are used prophylactically as they are of limited effectiveness when applied post infection. 

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Question

Why do insects present an increased chance of antibiotics being passed on to organisms later in the food chain, either through their direct consumption or consumption of their products?

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Answer

Insects metabolise antibiotics to a very limited degree, meaning they are more likely to be passed on.

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Question

What do antibiotics in ship paints prevent? 

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Answer

Bio-fouling

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Question

What do antibiotics disrupt the formation of to prevent biofouling?

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Answer

Biofilms, colonies of bacteria and other microorganisms held together with secreted extracellular polymers. 

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Why must biofouling be prevented?

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Answer

Biofouling must be prevented as it increases the drag the ship experiences, slowing it down and increasing fuel consumption. 

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Question

Why are antibiotics used in microbial culture?

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Answer

Antibiotics are used in microbial culture to prevent contamination or select for bacteria which have successfully taken up genetic material. 

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Question

What is the term given to the release of antibiotics into the environment?

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Answer

Antibiotic pollution. 

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