An analysis of sensitivity to antibiotics is mandatory if the doctor suspects that the patient’s disease is bacterial in nature. This is due to the fact that doctors are trying to control the purpose of these drugs, so as not to stimulate mutations and not cause resistance in microorganisms.
Definition
An antibiotic susceptibility test is a laboratory way to identify a drug that will have the greatest effect on the pathogenic flora in this particular case of the disease.
At the moment, antibiotic therapy is used quite widely where it is needed, as well as in cases where it is not necessary at all, for reinsurance against possible complications. For example, after cesarean section, laparoscopic surgery, removal of calculi from the kidneys or ureters, etc.
The pharmaceutical industry can offer a wide selection of drugs, both in terms of price and in terms of effectiveness. In order not to “poke a finger into the sky” and prescribe an effective antibiotic, it is necessary to sow sensitivity.
Indications
Before the doctor selects therapy, the patient needs to undergo some tests. Inoculation for sensitivity to antibiotics is prescribed if it is necessary to determine the medicine, which in this case will be most appropriate. Most often, this study is prescribed to treat sexually transmitted diseases or STDs. For children, the need for an antibiotic is a prerequisite.
In addition, the determination of sensitivity is necessary to avoid the resistance of bacteria to treatment. If the patient was recently treated with antibiotics, and now a second course is again required, then a replacement of the drug is required. This will allow you to use smaller doses of the drug and not cause mutations in the pathogen. In purulent surgical wards, antibiotics are changed every two to three months.
This analysis is necessary even if an allergic reaction occurs to the main group of antibiotics in the patient.
Diffusion methods
Urinalysis for sensitivity to antibiotics, and not only it, can be done in several ways. The first one is the disk method. Spend it as follows. Agar is poured into a Petri dish, and when it solidifies, the studied material is applied with a special tool. Then, paper discs soaked with antibiotics are laid out on the agar surface. After the cup is closed and placed in a thermostat. Gradually, the disk is immersed in gelatin, and the antibiotic diffuses into the surrounding space. Around the paper, a “growth suppression" zone is formed. The cups are held in a thermostat for twelve hours, then they are removed and the diameter of the above zone is measured.
The second method is the E-test method. It is similar to the previous one, but instead of paper disks, a strip is used, which in its course is saturated with antibiotic to varying degrees. After twelve hours of exposure in a thermostat, a Petri dish is taken out and they look at where the growth suppression zone is in contact with a strip of paper. This will be the lowest concentration of the drug that is needed to treat the disease.
The advantage of these tests is the speed and simplicity of their conduct.
Breeding methods
Analysis of flora and sensitivity to antibiotics can be done in another way. This method is based on a sequential decrease in the concentration of the antibiotic (from maximum to minimum) in order to determine in which tube the inhibition of bacterial growth stops.
First prepare the drug solutions. Then they are introduced into a liquid medium with bacteria (broth or agar). All tubes for the night (i.e. 12 hours) are placed in a thermostat at a temperature of 37 degrees, and in the morning they analyze the results. If the contents of the test tube or Petri dish are cloudy, this indicates the growth of bacteria and, therefore, the antibiotic is ineffective in this concentration. The first tube, in which the growth of colonies of microorganisms will not be visually determined, will be considered a sufficient concentration for treatment.
This dilution of the drug is called the minimum inhibitory concentration (IPC). It is measured in milligrams per liter or micrograms per milliliter.
Interpretation of Results
An analysis of sensitivity to antibiotics must be able to not only be done correctly, but also correctly decrypted. Based on the results obtained, all microorganisms are divided into sensitive, moderately resistant and resistant. In order to distinguish between them, conditional borderline concentrations of drugs are used.
These values are not constant and may vary depending on the adaptability of microorganisms. The development and revision of these criteria is entrusted to chemotherapists and microbiologists. One of the official structures of this kind is the US National Committee for Clinical Laboratory Standards. The standards they developed are recognized worldwide for use in evaluating antibiotic activity, including for randomized multicenter studies.
There are two approaches to assessing the results of an analysis of sensitivity to antibiotics: clinical and microbiological. Microbiological assessment focuses on the distribution of effective concentrations of antibiotic, and clinical - on the quality of antibiotic therapy.
Resistant and sensitive microorganisms
Analysis - the determination of sensitivity to antibiotics - is prescribed to identify sensitive and resistant microorganisms.
Pathogens that respond to antibiotic treatment at an average therapeutic concentration are called sensitive. If reliable information on the sensitivity category of the microorganism is missing, then data obtained in the laboratory are taken into account. They are combined with knowledge of the pharmacokinetics of the drug used, and after synthesis of this information, a conclusion is made about the susceptibility of bacteria to the drug.
Resistant, that is, resistant, microorganisms include those bacteria that continue to cause disease even when using maximum concentrations of drugs.
Intermediate resistance is established if the disease during treatment can have several outcomes. Recovery of the patient is possible in the case of using high doses of antibiotics or in the case of targeted accumulation of drugs at the site of infection.
Minimum bactericidal concentration
Analysis of microflora and sensitivity to antibiotics determines such an indicator as the minimum bactericidal concentration, or MBC. This is the lowest concentration of the drug, which under laboratory conditions causes the elimination of almost all microorganisms within twelve hours.
Doctors use the knowledge of this indicator when prescribing therapy is not bactericidal, but bacteriostatic drugs. Or in cases where standard antibacterial therapy is ineffective. Most often, this analysis is ordered for patients with bacterial endocarditis, osteomyelitis, as well as opportunistic infections.
What could be a pattern?
Antibiotic susceptibility testing can be performed using body fluids:
- saliva;
- blood;
- urine;
- sperm;
- breast milk.
In addition, smears are taken from the urethra, cervical canal and upper respiratory tract to determine local sensitivity.
Analysis Preparation
Tank. antibiotic susceptibility testing does not require substantial preparation from patients, but there are still some limitations.
- For research, an average portion of morning urine is used, which is collected in sterile dishes. Before this, the patient must necessarily exercise the toilet of the external genital organs and hands.
- Breast milk is collected before feeding the baby. The first portion is drained, and then several milliliters from each breast are decanted into a sterile container.
- Before passing a smear from the nasopharynx, you should refrain from eating for five to six hours.
- In the case of taking a smear from the genital tract, it is recommended to refrain from sexual intercourse for a couple of days.
To date, there are no clinical or laboratory methods that could absolutely predict the effect of antibiotic therapy. But at the same time, determining the sensitivity of bacteria to drugs can be a guide for doctors in the selection and correction of treatment.