Antibiotic – Definition, mechanism of actions and medical uses

Definition

An antibiotic is a natural, semi-synthetic or synthetic material capable of inhibiting the growth of bacteria or destroying them. These medicines are used to treat infections caused by pathogenic bacteria. Their action relies on interfering with biological mechanisms that are essential for bacterial function, such as synthesis of cell wall, protein production or DNA replication.

Antibiotics don’t act against viruses, mushrooms or parasites. They are prescribed only for confirmed or strongly suspected bacterial infections. The first medicine came from micro-organisms capable of naturally producing antibacterial substances to limit environmental competition.

The effectiveness of an antibiotic depends on several factor: its susceptibility to the bacterium, its concentration in the organism and the length of the treatment. Some antibiotics have a narrow spectrum, targeting a limited number of bacterial species. Other have a broader spectrum and are effective against many types of bacteria. Their use represents a cornerstone of modern medicine in the treatment of serious infections.

Origin and context of use

Antibiotic’s history starts with the observation of antimicrobial substances produced by some micro-organism. In 1928, Alexander Flemming identifies the antibacterial effect of penicillin obtained from penicillium moulds. This discovery paved the way for the development of effective treatments against many infections that were once fatal.

Clinical use of antibiotics became widespread during the 40s with the industrial production of penicillin. The following decades saw the birth of new types of antibiotics such as tetracyclines, macrolides or cephalosporins. These drugs profoundly changed how bacterial infections were handled.

Antibiotics are now used in both human and veterinary medicine. Their prescriptions rely on clinical, microbiological and pharmaceutical criteria. Laboratories identify bacteria responsible for a said infection and assess their susceptibility to different drug molecules using tests known as antibiograms.

The massive distribution of antibiotics also led to the appearance of bacterial resistance, becoming a major public health issue.

How does it work?

Antibiotics target structures or functions specific to bacteria. This explains their capacity to eliminate bacteria while preserving human cells.

Some molecules stop bacterial cell wall synthesis. It is the case for beta-lactams, such as penicillin. The cell wall guarantees the rigidity of the bacteria and protect it. When its synthesis is inhibited, bacterial cell becomes fragile and eventually bursts.

Other antibiotics inhibit the production of protein necessary for the bacteria. Macrolides, tetracyclines and aminoglycosides attach themselves on the ribosome of a bacteria, which is the structure in charge of the protein production. And when it does the protein synthesis stops.

Some medicine disrupts the replication of the bacterial genetic material. Fluoroquinolones obstruct enzymes necessary to the DNA duplication, avoiding the proliferation of bacteria.

Antibiotics can be either bactericidal or bacteriostatic. The former killing directly the bacteria. The latter slowing their growth, giving time to the immune system to get rid of the infection.

The diffusion of the drug in the tissues, its concentration and the length of the treatment influence the therapeutic efficiency.

When is an antibiotic used?

Antibiotics are prescribed to treat confirmed or highly suspected bacterial infections. Their use depends on the types of bacteria, the site of infection and the patient’s health status.

They are used in a wide range of medical situations:

Bacterial respiratory infections such as some pneumonia

Urinary tract infections caused by intestinal bacteria

Skin and soft tissue infections

Bacterial gastrointestinal infections

Bacterial meningitis

Septicaemia, generalised bloodstream infections

Antibiotics are also used as prevention in some high-risk situations. Antibiotic prophylaxis may be administered before certain surgical procedures to reduce the risk of postoperative infection.

The choice of certain molecule relies on the antibacterial spectrum, the susceptibility of the micro-organism and the patient’s characteristics, including age, allergies or renal function.

Benefits and aim

The use of antibiotics aims to quickly control bacterial infection and prevent their complications. These medicines have deeply reduced mortality related to infection since the mid 20^th century.

Main objectives:

✓ to kill the bacteria responsible for the infection

✓ to reduce symptoms associated with inflammation and bacterial proliferation

✓ to prevent spreading the infection to other organs

✓ to limit serious complications such as septicaemia

✓to shorten the duration of the illness and facilitate recovery

Antibiotics also allow to secure many modern medical practises. Surgical interventions, anti-cancer treatment or organ transplantation carry a high-risk of infection. Antibiotics contribute to reduce this risk.

Risks, limits or controverses

There are several limitations to the use of antibiotics. The appearance of bacterial resistance being the most important one. Bacteria may develop mechanism allowing them to neutralize the action of medicines, making some of them ineffective.

Bacterial resistance can emerge when antibiotics are used excessively, at insufficient doses, or to treat viral infections against which they are ineffective.

Some adverse effects may appear, for the most part this include digestive disorders, allergic reaction, or alteration in the intestinal microbiota.

And some antibiotics may cause more specific adverse effects, such as renal, hepatic or auditory damage depending on the medicine used.

Such limitations have led to the development of appropriate-use strategies to preserve the effectiveness of existing antibiotics.

Research and innovations

Scientific research on antibiotics is focusing on several complementary areas. The first being to develop new medicines capable of bypassing the bacterial resistance mechanism. Researchers study compounds derived from soil micro-organisms, marine bacteria or chemical synthesis.

Another area of research focus on the use of existing antibiotics. Strategies include precise dose adjustment, the combination of several drug and the adaptation of the treatment based on fast microbiological analyses.

Technologies of molecular diagnosis allow faster identification of bacteria responsible of an infection and their resistance.

Alternative approaches are also studied, such as bacteriophage therapy, the use of antimicrobial peptides or microbiome modulation. These strategies aim to complete or reduce the use of classical antibiotic.

Frequently asked questions

Do antibiotics work against viruses?

 No, they don’t. Antibiotics target specific structures for bacteria, such as the cell wall or bacterial ribosomes. Viruses use human cell to replicate and do not possess these structures. Viral infections, such as the flu or the cold, are not treated with antibiotics.

Why is it important to do the treatment all the way?

Stopping treatment too soon may allow some bacteria to survive. These remaining bacteria can multiply and cause a relapse of the infection. They may also develop resistance to the antibiotic, making it less effective for future infections.

What is antibiotic resistance?

Antibiotic resistance means the ability of bacteria to survive despite the presence of an antibiotic. It may arise from a genetic mutation or from the acquisition of resistance genes from other bacteria. This phenomenon reduces the effectiveness of available treatments.

Do antibiotics affect intestinal microbiota?

Yes, they do. Antibiotics may modify the balance of the intestinal microbiota by killing some beneficial bacteria. It may cause digestive disorders, such as diarrhoea, or even stimulate the proliferation of other micro-organisms.

 Is it possible to be allergic to antibiotics?

Some people may have allergic reactions to antibiotics, particularly penicillin. Symptoms may include skin rashes, swelling or breathing difficulties. If an allergy is diagnosed, it should be reported to the doctor to prevent the prescription of related medicine.

Why do some antibiotics have a broad spectrum?

A broad-spectrum antibiotic acts against a large number of bacteria. It is often used when the bacteria responsible for the infection is not clearly identified. Once the infectious agent is detected, a more targeted antibiotic may be preferred.

What is an antibiogram?

An antibiogram is a laboratory test allowing to assess the susceptibility of a bacterium to different antibiotics. The bacterium is isolated and exposed to several antibiotics in order to identify those stopping its growth.

Can antibiotics prevent infections?

Yes, it can in some specific situations. Antibiotic prophylaxis may be used before some surgical procedures or for patient at high risk of infection. It is strictly controlled to avoid any unnecessary prescriptions.

How long does an antibiotic remain active in the body?

The length of action depends on the medicine and its pharmaceutical half-life. Some antibiotics need to be taken several times a day to keep an effective concentration in the blood, while others can be taken once a day.

Why do doctors sometimes avoid prescribing antibiotics?

When the infection is viral or mild, antibiotics do not have any therapeutic benefits. Avoiding unnecessary prescriptions limits the emergence of bacterial resistance and reduces exposure to adverse effects.

Key points

Antibiotics are medicines made to treat bacterial infections by inhibiting bacterial growth or killing bacteria. They rely on targeting biological mechanisms specific to bacteria, such as cell wall synthesis or protein production. Their use has profoundly transformed modern medicine by reducing mortality related to infection diseases. However, their effectiveness relies on appropriate use. The rise of bacterial resistance is now a major public health issue, which imply appropriate prescription and careful microbiological monitoring.

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