Analysis for sensitivity to antibiotics: the essence, how to take, decipher

An analysis of susceptibility to antibiotics is mandatory when a doctor suspects that the patient's disease is bacterial in nature. This is due to the fact that physicians try to control the appointment of these drugs, so as not to stimulate mutations and not cause resistance in microorganisms.

Definition

The antibiotic sensitivity test is a laboratory method of identifying 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 widely enough where it is needed, and also when it is not necessary, for reinsurance against possible complications. For example, after cesarean section, laparoscopic operations, removal of concrements from the kidneys or ureters, etc.

The pharmaceutical industry can offer a wide range of drugs both in terms of price and in terms of effectiveness. In order not to "poke a finger in the sky" and designate an effective antibiotic, you need to plant crops for sensitivity.

Indications

Before the doctor selects therapy, the patient needs to pass some tests. Sowing 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 for the treatment of sexually transmitted diseases, or STDs. For children, however, the need for an antibiotic is a prerequisite.

In addition, the definition of sensitivity is necessary to avoid the resistance of bacteria to treatment. If a patient has recently been treated with antibiotics, and now a second course is needed again, then a replacement of the drug is required. This will allow using smaller doses of the drug and not causing a mutation in the pathogen. In purulent surgical units, antibiotics are changed every two to three months.

This analysis is necessary in the event that the patient has an allergic reaction to the main group of antibiotics.

Diffusion methods

Urine analysis for sensitivity to antibiotics, and not only her, can be done in several ways. The first of these is the disk method. Conduct it as follows. Agar is poured into the Petri dish, and when it is cold, the test material is applied with a special tool. Then, on the surface of the agar, paper discs, impregnated with antibiotics, are laid out. After the cup is closed and put in a thermostat. Gradually, the disk is immersed in gelatin, and the antibiotic diffuses into the surrounding space. A zone of "growth suppression" is formed around the paper. 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 discs use a strip, which on its length is impregnated with antibiotic in various degrees. After twelve hours of exposure in a thermostat, the Petri dish is taken out and looked at where the growth suppression zone comes 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.

Methods of breeding

Analysis of flora and sensitivity to antibiotics can be done in another way. This method is based on a consistent reduction in the concentration of the antibiotic (from maximum to minimum) in order to determine which of the tubes stops the containment of bacterial growth.

First, prepare the drug solutions. Then they are introduced into a liquid medium with bacteria (broth or agar). All tubes at night (that is 12 hours) are placed in a thermostat at a temperature of 37 degrees, and in the morning they analyze the results obtained. If the contents of a test tube or a Petri dish are turbid, this indicates the growth of bacteria and, consequently, the ineffectiveness of the antibiotic at a given concentration. The first test tube, in which the growth of the colonies of microorganisms will not be determined visually, will be considered sufficient concentration for treatment.

This dilution of the drug is usually called the minimal suppressive concentration (MIC). It is measured in milligrams per liter or micrograms per milliliter.

Interpretation of results

Analysis for sensitivity to antibiotics must be able not only to correctly do, but also intelligently decipher. Based on the results obtained, all microorganisms are divided into sensitive, moderately resistant and resistant. In order to distinguish them among themselves, conditional borderline drug concentrations are used.

These values are not constant and can vary depending on the adaptability of the microorganisms. The development and revision of these criteria is entrusted to deal with chemotherapists and microbiologists. One of the official structures of this kind is the National Committee for Clinical Laboratory Standards in the United States. The standards they have developed are recognized worldwide for use in assessing antibiotic activity, including for randomized multicenter trials.

There are two approaches to evaluating the results of antibiotic susceptibility testing: clinical and microbiological. Microbiological evaluation 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 assigned to identify sensitive and resistant microorganisms.

Sensitive are called pathogens, which can be treated with antibiotics in an average therapeutic concentration. If there is no reliable information on the sensitivity category of the microorganism, then the data obtained under laboratory conditions are taken into account. They are combined with knowledge of the pharmacokinetics of the drug used, and after the 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 the maximum concentrations of medicinal substances.

Intermediate resistance is established in the event that 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 the drug at the site of infection.

The minimum bactericidal concentration

Analysis for microflora and sensitivity to antibiotics determines such an indicator as the minimum bactericidal concentration, or MBK. This is the lowest concentration of the drug, which under laboratory conditions causes elimination of almost all microorganisms within twelve hours.

Knowledge of this indicator doctors use when they designate therapy is not bactericidal, but bacteriostatic medicines. Or in cases where standard antibiotic therapy is ineffective. Most often, this analysis is ordered for patients with bacterial endocarditis, osteomyelitis, as well as opportunistic infections.

What can be a model?

An analysis of sensitivity to antibiotics can be carried out using biological fluids:

- saliva;

- blood;

- urine;

- semen;

- breast milk.

In addition, for the detection of local sensitivity, smears are collected from the urethra, cervical canal and upper respiratory tract.

Preparation for analysis

Tank. The analysis for sensitivity to antibiotics does not require patients to prepare much, but there are some limitations.

1. The study uses an average portion of morning urine collected in sterile dishes. Before this, the patient must necessarily carry out the toilet of the external genital organs and hands.
2. Breast milk is collected before feeding the baby. The first portion is drained, and then a few milliliters are poured into each sterile container from each breast.
3. Before delivery of a smear from a nasopharynx it is necessary to refrain from reception of food within five-six hours.
4. In the case of taking a smear from the genital tract, it is recommended to abstain from sexual intercourse for a couple of days.

To date, there are no clinical or laboratory methods that would with 100% probability 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 choice and correction of treatment.