Antibiotics, also called antibacterials, are medicines that act against bacteria within the context of infections.

Antibiotics slow down the growth of bacteria (bacteriostatics) or kill them (bactericides), in humans, animals and plants. 

Antibiotics act on bacteria in a specific way, by blocking an essential stage of their development. There are different classes of antibiotics, depending on their mode of action.

A bacterium can be more or less sensitive to an antibiotic. However, an antibiotic therapy always acts on all of the microbiota, the community formed by bacteria, as well as on other microbes such as parasites, fungi and viruses.

Among other things, antibiotics upset the balance between good and bad bacteria. When certain bacteria are killed, others develop resistance and are given more room to multiply. 

DID YOU KNOW? Antibiotics, which have been widely used since the second world war, have made it possible to reduce mortality associated with infectious diseases such as tuberculosis and the plague. 

Bacteria are naturally present within our body, in animals and in the environment.

Our bodies are host to over one hundred bacterial species that form different communities with other microbes: cutaneous microbiota, gut microbiota, vaginal microbiota, pulmonary microbiota, etc. 

Most bacteria play a beneficial role and protect us against dangerous infections.

But when the immune system is weakened or when bacteria enter the body by an unusual route, some bacteria can become ‘pathogens’ and cause infections. 

For example: the bacterium Escherichia coli, which is naturally present in the gut, can cause a urinary infection if it enters the bladder. 

Resistance to antibiotics is the capacity of a bacterium to resist the action of an antibiotic.

Bacteria are very powerful microbes: they are plentiful, multiply quickly, adapt to their environment and learn to defend themselves, in particular by resisting antibiotics.

When they are exposed to antibiotics, sensitive bacteria are killed and leave space for resistant bacteria which can continue to develop and multiply.

A large number of infections contracted in hospital (nosocomial infections) are caused by antibiotic-resistant bacteria:

Antimicrobials are the group of medicines that fight microorganisms:

• antibacterials or antibiotics used against bacteria (pneumonia, pyelonephritis, tuberculosis, etc.)
• antivirals against viruses (flu, HIV, herpes)
• antifungals used against fungi (Candida)
• antiparasitics used against parasites (malaria).

Viruses, parasites and fungi can also develop resistance to antimicrobials  

Certain antimicrobial agents act on all microbes, albeit temporarily:

• disinfectants are intended for inert matter (surfaces, instruments) 
• antiseptics for live tissue (skin, mucous membranes).  

The development of resistance to disinfectants and antiseptics is less common than that which is observed with antibiotics.

However, there are risks of cross-resistance: overexposure to disinfectants and antiseptics can reduce the effectiveness of antibiotics for certain bacterial infections.