Antibiotics are one of the most important therapeutic discoveries in the history of medicine, revolutionizing the way bacterial infections are treated and reducing the mortality and morbidity associated with them.
However, the uncontrolled use of antibiotics has led to the development of bacterial resistances, reducing treatment options for certain infectious diseases.
Inappropriate use of antibiotics is a serious public health problem worldwide, as it increases the risk of selecting resistant bacteria or resistance determinants.
Indiscriminate use of antibiotics favours the survival of bacteria carrying resistance genes, while sensitive bacteria die, leaving an ecological niche for resistant bacteria to proliferate.
1 – APPEARANCE
Actions that encourage the emergence of resistance:
2 – PROPAGATION
This resistance can spread rapidly through the exchange of genetic material between different bacterial species, and these resistant bacteria circulate between humans and animals through food, water and the environment.
3 – AMPLIFICATION
Improper handling operations in intensive livestock production systems play an important role as resistance amplifiers, regardless of their origin, and poor biosecurity has been found to favour the spread of resistance.
CONSEQUENCES OF ANTIBIOTIC RESISTANCE
WHAT SHOULD WE BASE OUR CHOICE OF ANTIBIOTIC ON?
MINIMUM INHIBITORY CONCENTRATION – MIC
The MIC of an antibiotic is the minimum concentration needed to STOP the growth of a “test” microorganism in a standard inoculum.
MINIMUM BACTERICIDAL CONCENTRATION – MBC
The BMD of an antibiotic is the minimum concentration needed to ELIMINATE a “test” microorganism in a standard inoculum.
The determination of MIC and MBC allows to establish which is the minimum dose of antibiotic effective against a given pathogen
By subjecting the bacteria to different dilutions of the antibiotic, it is possible to determine the MIC and the MBC.
MIC is considered to have been reached when there is no longer growth of the bacteria in the culture medium with the antibiotic in question.
MBC is reached when, when the bacteria incubated in the antibiotic broth are seeded on antibiotic-free agar, no bacterial growth occurs.
An antibiogram is performed to determine the sensitivity of a bacterium to different antibiotics (Figure 2):
The bacterium is sown in an antibiotic-free growth medium.
Discs impregnated with the antibiotics to be tested are placed.
After the incubation period, the inhibition halo (area of the agar around each disc where there is no bacterial growth) is determined, so that the greater this halo, the greater the sensitivity of the bacteria to the antibiotic present in the disc.
TYPES OF ANTIBIOTICS
Antibiotics are classified according to their mechanism of action and their therapeutic behaviour.
MECHANISM OF ACTION OF THE ANTIBIOTIC
The mechanism of action of the antibiotic largely determines the effectiveness of the treatment. We can find two main groups according to their activity:
BACTERICIDES : They cause the death of the microorganisms responsible for the infectious process.
BACTERIOSTATICS : They inhibit the bacterial growth, although the microorganism remains viable, so that when the treatment is suspended, it can multiply again.
There is a relationship between the plasma concentration of the drug and the antimicrobial activity that marks its effectiveness against bacteria, so we can classify these products according to their therapeutic behavior, that is, “how they eliminate or inhibit the growth of bacteria:
DEPENDENT CONCENTRATION” EFFECT : The increase in the concentration of the drug above the MIC, against a certain pathogen, increases the mortality of the bacteria.
DEPENDENT TIME” EFFECT : The increase in the concentration of the drug above the MIC, against a certain pathogen, does NOT significantly increase the mortality of the bacteria. In this case, the effect of the antibiotic depends on the time of exposure of the bacteria to the action of the drug.
RATIONAL USE OF ANTIBIOTICS
Prudent use of antibiotics implies:
Significantly reducing the use of antimicrobial products as preventive treatment.
Limiting the therapeutic use of antibiotics to those cases where all available tools have been applied to identify the agent involved in order to establish a definitive diagnosis.
To meet this challenge that involves establishing a critical point control system:
Monitoring of treatments
Recording and control of treatments
STEPS TO BE CONSIDERED
To make a correct management of the prevention of the spread of resistances, having the hygiene and the vaccines as barriers for the prevention of the spread of resistances.
In there is an infectious outbreak, decide whether it is appropriate to treat or not.
If we decide to treat, the critical point is the choice of treatment:
Once the drug to be used has been chosen, decide:
Administer the medication properly:
Record the treatments in the farm book.
Training of all those who handle the medicines.
NATIONAL PLAN FOR ANTIBIOTIC RESISTANCE: the Spanish example
To reduce the contribution of antibiotic use in human and veterinary medicine to bacterial resistance.
To preserve the existing therapeutic arsenal.
Adapted from the conference offered by Margarita Arboix (UAB Rector) in porciFORUM 2017
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