Antibiotic Resistance and Antibiotic Choice
Resistant microbial strains can:
- Produce drug-modifying enzymes (for example, beta-lactamases);
- Change the structure on which the drug acts;
- Use a metabolic line other than the inhibited one;
- Change the cell permeability, preventing the passage or the adhesion of the molecule with antibiotic action.
The R GENE, which transmits resistance to antibiotics, is found in plasmids and in particular in TRANSPOSONS (therefore the transposon can be found in the plasmid but also integrated in the chromosome of the resistant bacterium).
For further information see the dedicated article: Bacteria: genetics and mechanisms of transfer of genetic informationof the organism, usually constituted by GRAM -. It should also be remembered that the antibiotic itself does not create resistance (which derives from mutations and gene transfer), but selects it. On the other hand, resistance is not a phenomenon of adaptation to an antibiotic, but an event - spontaneous and transmissible - which affects the genetic heritage of the bacterium.
To choose the most appropriate antibiotic in each situation, it is necessary to isolate the bacterium through the use of appropriate analyzes and tests (sampling with swabs, biopsies, etc.).The bacteria are then made to replicate in suitable culture media; then the various antibiotics are tested through a method called antibiogram.
The bacteria are then spread (technical term plated or inoculated) in a petri dish containing agar medium (solid), inside which absorbent paper discs (called bibula) are distributed. Each of these discs is soaked in a specific antibiotic. After 24 hours the bacterial growth around the disk is evaluated: the greater the inhibition radius, the more effective that antibiotic will be.
There are two types of antibiograms, one direct and one indirect. The first is performed directly on the pathological material and has the big disadvantage of not being selective (we know that a certain antibiotic was more or less effective than another in reducing the microbial population, but we do not know how active it is against the single pathogen) . In the indirect one, on the other hand, the pathological agent is first isolated from the sample and the various tests are performed only on it.
To stem the phenomenon of antibiotic resistance, the collaboration of the patient is also important, who must continue the therapy until the time established by the doctor without interrupting it - as often happens - at the first signs of improvement.