If they remain without action on virus, Antibiotics inhibit or destroy a large number of micro-organisms: bacteria or protozoa. There are also substances of similar chemical structure that are active on fungi, but these substances are not contained in what is commonly known antibiotic drugs.
Their action against bacteria
Bacteria are living beings formed a single cell. They are absolutely everywhere in our environment: in soil, water, on everyday objects in our food, etc.. All bacteria are not dangerous and only some of them are called pathogens, that is to say can cause infection more or less serious. Many species are not dangerous: eg some live on our skin, as Staphylococcus White said they are "commensal. Others live in our intestines and constitute the intestinal flora, which maintains a balance favorable to digestion and limit the growth of other bacteria that are harmful.
Many bacteria are useful as LactobacillusWhich allows the manufacture of yoghurt. Other species can purify waste water by degrading organic matter and consume the main pollutants (nitrates, for example).
Antibiotics work on bacteria in different ways. Some prevent the formation of their protective coverings (membrane wall). Other substances act by blocking certain chemical reactions required for their Metabolism. Finally, some antibiotics inhibit the translation of genetic information (genes) proteins.
How class-t-on bacteria?
The classification of bacteria is modeled on that of all life forms: class, order, family, genus, species and even strains, for certain. This systematic and careful identification is restricted to specialists, we can classify bacteria more easily.
It differs primarily bacteria "pathogens"They regularly trigger a specific disease, they develop and cause an infection. For example, Vibrio cholerae is bacteria causes cholera. Other bacteria are called "opportunistic"Because they cause infectious diseases in specific circumstances. This is the case of its kind Clostridium, Which contains many species and some strains cause intestinal infections in patients weakened.
Other distinctions can be among the many forms of bacteria. This is the case of called Gram staining which is either positive or negative. It is a procedure complex (developed in 1884) which colors in purple bacteria where the wall is thick and impermeable (Gram positive) And pink bacteria whose wall is rich in fat and more permeable (Gram negative). This distinction is still used in infectious diseases: certain antibiotics act only on Gram-positive bacteria, for example.
Finally, we can separate the bacteria according to their Metabolism: Some need oxygen, they said aerobic and some do not need, they are anaerobic. Again, the distinction is important when it comes to setting up treatment.
Antibiotics have helped with vaccination, reducing the mortality from diseases caused by pathogenic bacteria. According to WHO, TB is the only disease caused by bacteria which is still among the top ten causes of death worldwide among adults. This does not mean that these diseases have disappeared, far from it. Certainly, routine immunization pushed several major diseases, such as diphtheria or Tetanus. But there is still the occurrence of epidemics (cholera or typhoid, for example) following natural disasters or wars, especially in the poorest countries. Antibiotics used to control outbreaks of bacterial diseases in the bud and very large epidemics of the past. They give way today to viral diseases like AIDS or parasitic diseases, such as Malaria.
The opportunistic bacteria
Some bacteria present in environmental or commensal (which we host) without damage under normal conditions, can become pathogenic in favor of lower immunity, another illness or medication that gives them the opportunity to develop. This is the case, for example, meningococci (Neisseria meningitidis) Which is present in the flora of the nose and pharynxAnd that causes a Meningitis rarely (one healthy carrier of 10 000 triggers a Meningitis). Several bacterial species belonging to the intestinal flora can also be opportunistic, as Escherichia coliEg.
The bacteria are highly opportunistic and many are multiple opportunities to develop depending on environmental conditions and health of their host. Some species in the environment, have a disturbing profile, because they occur regularly can cause infections called Nosocomial (see box), that is to say, contracted at the hospital for care or surgery. This is the case of Gram-negative aerobic bacteria, such as Pseudomonas or Acinetobacter. Usually non-pathogenic, they thrive in the particular context of the hospital and are often resistant to many antibiotics.