FAQ Infections & Antibiotics


Antibiotics are medications used to treat infectious bacterial disease. They can either kill the bacteria (bactericidal) or inhibit their growth (bacteriostatic). They have no effect on infections caused by viruses (e.g. a cold or the flu) but they can be presecribed to treat concomitant bacterial infections.

Antibiotics exploit characteristics that are typical of bacteria. For example, they target structures or mechanism in the bacterial cells that are not present in other lifeforms, making them more or less well tolerated by humans and animals. Bacteria have, for example, a cell wall made up of murein or peptidoglycan, a molecule that is only present in bacteria. They also use different structures and enzymes to humans and animals to manufacture proteins and replicate their hereditary material.

Some antibiotics target the construction of new bacterial cell wall components while others interrupt metabolic processes or the replication of hereditary material.

There are about 15 different antibiotic groups that differ in their chemical structure and mode of action and thus also in their efficacy against certain pathogens

Antiobiotics can be classified on the basis of different criteria such as

  • their efficacy
  • their chemical structure
  • their mode of action.

Selected groups of antibiotic and the microorganisms they affect are shown in the document below:

Reserve antibiotics are antibiotics that are only supposed to be used for infections that are particulary severe and/or the infectious bacteria have developed resistance to other antibiotics. As far as possible, they should not be used for infections with a simple course to avoid the development of resistance.

Reserve antibiotics are no more effective than other antibiotics but because of their relatively rare and controlled use, fewer bacteria have developed resistance to them. They often cause considerably more side effects than conventional antibiotics.

Vancomycin is, for example, the reserve antibiotic against Staphylococcus aureus.

The standard antibiotics are about a dozen preparations that have been used for years or decades to control microbial infections. Relevant lists from the WHO or individual countries and regions differ.

The standard antibiotics include

  • aminoglycoside antibiotics,
  • cephalosporins,
  • gyrase inhibitors,
  • macrolide antibiotics,
  • penicillins,
  • sulfonamides,
  • tetracyclines,
  • trimethoprim and
  • tuberculostatic drugs

They are used to control practically all bacterial infections and are therefore important across all medical disciplines.

The minimum inhibitory concentration (MIC) is defined as the lowest concentration of an antibiotic that will inhibit the visible growth of the microorganisms. It is stated as microgram per millilitre (μg/mL) and is used to define the dosage of antibiotics.

Concentrations of the active substance for locally and systemically administered antibiotics
Fig.: Concentrations of the active substance for locally and systemically administered antibiotics

Unlike antibiotic therapy in which antibiotics are used to control existing infections, medications used for antibiotic prophylaxis are administered before, during or immediately after a medical procedure to prevent an infection developing. The choice of suitable antibiotic is made empirically based on past experiences of which pathogens are likely to be present and taking into account the local epidemiology of resistance. This affects predominantly orthodontic/orthopaedic, trauma or dental procedures and/or at-risk patients with a weakened immune system.

Antibiotic prophylaxis can involve either systemic or local administration of antibiotics with a combination of both types of administration also possible. With local administration, there may be very high antibiotic concentrations present in the affected area while the systemic load remains low. Combining systemic and local administration of antibiotics for infection prophylaxis is a well-established procedure, particularly in orthopaedics and trauma surgery.

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