Intestinal infections are a large group of diseases caused by pathogenic or opportunistic bacteria, viruses and protozoa. The leading symptom of such pathologies is diarrhea. Such diseases are very widespread in the world, including developed countries.
All intestinal infections are treated in the same way, so the identification of a specific pathogen is important not for the attending physician, but for epidemiologists who study the ways of spread, transmission methods, manifestations of the disease in each new case, the effectiveness of treatment and other characteristics of the bacterium or pathogen virus. This information is extremely important given the wide spread of intestinal infections on the planet and their high contagiousness, as bacteria and viruses change. In addition, the pathogen is installed to understand what preventive measures need to be taken to prevent infection of other people.
One of the ways to identify an infectious agent is a bacteriological analysis of feces. It is carried out for anyvisits to the doctor with complaints of diarrhea. This is the most versatile way to identify the cause of an intestinal infection that does not require sophisticated equipment.
Bacteriological analysis of feces is based on the study of the physiological properties of the pathogen identified in the biomaterial. It includes cultivation, isolation of pure cultures, identification and typing of pathogens.
Classification of intestinal infections
Let's list the diseases that belong to the group of intestinal infections.
1. Caused by bacteria:
- Cholera.
- Botulism.
- Typhoid fever and paratyphoid fever (Salmonellosis).
- Schigillosis (dysentery).
- Escherichiosis (coliinfection).
- Other bacterial infections – campylobacteriosis, yersiniosis.
2. Caused by Protozoa:
- Amebiasis.
- Giardiasis and others
3. Caused by viruses:
- Rotavirus.
- Adenovirus.
- Norovirus and others
4. Caused by opportunistic pathogens:
- Staphylococci (there are conditionally pathogenic and pathogenic, for example, Staphylococcus aureus).
- Klebsiella.
- Citrobacter (there are pathogenic and opportunistic strains).
- E. coli.
- Proteus and others
5. Intestinal infections of unknown etiology.
6. Mixed intestinal infections.
In 40% of cases, the causative agent of intestinal infections are viruses, in 20% - bacteria, in 40% the pathogen failsinstall.
Acute intestinal infections are responsible for 30% of deaths in children under 5 according to WHO.
How to pass the test correctly
Preparation for the analysis of feces for bacteriological examination includes special rules:
- Using a special container to collect feces. Your doctor may provide you with a special culture tube and a sterile rectal loop.
- Preparing the ship - treat it with a disinfectant solution, rinse it several times with running water, pour boiling water over it.
- Do not touch the spoon, the inner walls of the container and the lid.
- Don't get tested after taking antibiotics.
- Carrying out a thorough toileting of the anus.
The sample must reach the laboratory as soon as possible. It is allowed to store the material for 2 hours at room temperature and 3 hours at a temperature of 2-8 °C. To identify some pathogens, it is necessary to inoculate on a nutrient medium immediately after taking the biomaterial.
Steps of bacteriological analysis of feces
1 day. Sowing material on differential diagnostic media.
These are special nutrient media used to identify groups of bacteria that differ in their ability to utilize a particular substance. For example, lactose is often added to the nutrient medium to grow pathogens of intestinal infections. Some bacteria (E. coli) break it down. Then colored colonies grow on the surface of the mediummicroorganisms. Some microorganisms do not break down lactose (Salmonella). Then unstained colonies grow.
2 day. The grown colonies are viewed under a microscope and described. Gram-stained and subcultured on other specific media to accumulate a pure culture of the pathogen.
3 day. Agglutination reactions are carried out with bacteria of pure cultures. Subculture cultures on other media (Gissa) to determine the enzymatic activity.
4 day. Evaluate the results of the agglutination reaction, growth on Hiss media. Based on the information received, they give a final answer about the type of pathogen present in the feces.
Deciphering the result
Standard fecal analysis for bacteriological examination includes the identification of several groups of bacteria. Particular attention is paid to Escherichia coli – its colonies with different enzymatic properties are reported separately. Most of these bacteria belong to the group of opportunistic pathogens. That is, they live in the intestine as saprophytes, but under certain conditions become pathogenic. A standard study also includes a bacteriological analysis of feces for dysbacteriosis. What bacteria can be found in the sample? This can be found in the analysis result below (as an example).
E. coli, or Escherichia coli (E. coli)
These microorganisms inhabit the large intestine of the child immediately after birth. Here they dominateamong facultative anaerobic bacteria. E. coli perform many useful functions in the human body. They contribute to the development of immunity to pathogenic varieties of bacteria, and also produce substances that inhibit the growth of other microorganisms.
Bacteria of the species E. coli are pathogenic and opportunistic. Under a microscope, one and the other look the same. They are distinguished by the structure of antigens located on the surface of bacteria. To do this, conduct a serological study. Opportunistic E. coli live in the large intestine, but against the background of immunodeficiency, they can cause inflammation in other organs, for example, in the urinary tract. Pathogenic representatives of E. coli are called diarrheagenic. They belong to transient bacteria, that is, they are not permanently localized in the body. When they enter the intestinal tract, they cause diseases under the general name of escherichiosis, the main manifestation of which is diarrhea.
Deciphering the results of determining the amount of E. coli
Standard bacteriological analysis of feces for the intestinal group of infections includes the following counts of the number of Escherichia coli:
- Total E. coli.
- Typical sticks.
- With mild enzymatic properties.
- Lactose negative.
- Hemolytic.
The total amount of Escherichia coli in 1 g of feces in children ranges from 400 million to 1 billion, and in adults - 300-400 million. Excessive multiplication of bacteria in the intestine leadsto dysbacteriosis.
Typical (classic) E. coli are good for the body. Their normal amount in the feces should be in the range 107-108. The decrease indicates intoxication, leading to the death of beneficial microflora in the large intestine, as well as colonization of the intestine by parasites - worms or protozoa. Other causes are high sensitivity to allergens, damage to the liver, kidneys, pancreas and thyroid glands.
The high content of these bacteria in the feces indicates their excessive reproduction, which can lead to the appearance of purulent inflammations of different localization.
E. coli with reduced enzymatic activity - "parasites". With normal immunity, they do not cause disease, but they do not bring benefits either. Such bacteria take the place of beneficial E. coli. As a result, the body receives less of a number of substances, including vitamins. Normally, there should be no more than 105. Their increase always indicates dysbacteriosis and can lead to inflammation.
Varieties of E. coli that do not ferment lactose (lactose-negative) are pathogenic. They attack the cells of the large intestine, causing diarrhea. The number of these bacteria in the feces should not exceed 105. If more of them are found in a patient with diarrhea, for example, 106 or 107, then these microorganisms were the cause of the disease. The inability to use lactose and some other properties make them related to Shigella - the causative agents of dysentery.
Hemolytic Escherichia coli arepathogenic, localized mainly in the caecum. Cause hemorrhagic colitis with symptoms of general intoxication (nausea, vomiting). Normally absent in feces.
Opportunistic pathogens that can cause intestinal infection
Increasingly, bacteria that constantly live in the human large intestine cause infections of various localization - the digestive tract, respiratory or genitourinary system. This is caused by the deteriorating environmental situation, the uncontrolled use of antibiotics and other drugs, the constant presence of bacteria in the human environment. As a rule, newborns and children of the first 6 months of life get sick.
You can perform a bacteriological analysis of feces in "Invitro". This is a network of laboratories, branches of which are in all major cities. Patients love that test results are available online, meaning they don't have to go to the lab to get them.
Staphylococci
There are three types of Staphylococcus bacteria that can cause intestinal infection:
- Staphylococcus aureus (Staphylococcus aureus).
- Epidermal.
- Saprophytic.
Staphylococcus aureus is the most pathogenic of them, that is, when it enters the body, it always causes the development of the disease. Therefore, in the analysis results, it is usually written as a separate line. Normally, there should be no Staphylococcus aureus in the stool. On theThe picture shows a view of a pure culture of Staphylococcus aureus under a microscope.
The epidermal species is also pathogenic, but it is less aggressive than golden, that is, it can be present in the body without damaging it. The saprophytic species is a common inhabitant of the large intestine. The total number of epidermal and saprophytic staphylococci should not exceed 104.
Pathogenic microorganisms causing intestinal infections
Bacteriological analysis of feces for pathogenic intestinal group includes the determination of bacteria of the genus Salmonella and the genus Shigella. They are pathogenic, that is, if they enter the intestines, they cause pathologies - salmonellosis, typhoid fever, dysentery. Normally absent in the body, therefore, they are not excreted in the feces.
Rarely, other pathogens that can cause intestinal infections are found in stool tests.
Viruses in stool analysis
In children of the first year of life, the causative agents of intestinal infections can be various viruses. When analyzing feces by microscopic and bacteriological methods, viruses are not detected.
Detection in the feces of pathogens of any intestinal infections requires hospitalization of children under 3 months of age. Hospitalization is also desirable for children under one year old.
When establishing dysentery, salmonellosis, staphylococcal infection, food poisoning, escherichiosis in adults and children older than a year, home treatment is prescribed. If the course of the disease is severe or there is a high risk of spreading the disease, patients are hospitalized in an infectious diseasehospital.
