LESSON 13 WHAT IS INFECTION Infection

LESSON № 13

WHAT IS INFECTION? Infection is the invasion of body tissues by disease-causing agents, their multiplication, and the reaction of host-tissues to the infectious agents and the toxins they produce. Infectious disease, also known as transmissible disease or communicable disease, is illness resulting from an infection. Hosts can fight infections using their immune system. Mammalian hosts react to infections with an innate response, often involving inflammation, followed by an adaptive response.

WHAT CAUSES INFECTIONS? Infections are caused by infectious agents including ØBacteria ØViruses ØFungi (ringworm) ØProtozoa ØMacroparasites (nematodes, tapeworms, helminths)

PROPERTIES OF INFECTIOUS AGENTS ØPathogenicity ØVirulence ØSpecificity ØOrganotropicity

PATHOGENICITY Pathogenicity is a specific sign of the pathogen, its potential to cause a specific infectious process under favorable conditions. On this basis, all states of microbes are subdivided into pathogenic, opportunistic and saprophytes. Pathogenicity and virulence are different concepts. A microorganism is considered virulent if it, when introduced into the animal's organism, even in small doses, causes the development of an infectious process.

VIRULENCE Virulence is the degree of pathogenicity of a particular microorganism, i. e. this is an individual characteristic. Virulence is a quantity that is measured (e. g. , minimum lethal dose DLM, median lethal dose LD 50).

SPECIFICITY Each infectious disease causes a specific pathogen. So, the causative agent of plague causes plague, cholera - cholera, etc. Infections (for example, purulent-inflammatory processes) caused by various microbes are known. On the other hand, one causative agent (for example, streptococcus) is capable of causing various lesions.

ORGANOTROPICITY Organotropicity is the defeat of cells, tissues and organs that are most suitable for their biochemical properties for life support of this type of microorganism.

VIRULENCE FACTORS 1. Adhesion to cells Many bacteria for infection of certain cells of the body, for example, intestinal epithelium should attach to them. It was found that a large number of host cell molecules, in particular, and the receptors of bacteria (proteins of the outer bacterial membrane) are involved in this process.

VIRULENCE FACTORS 2. Invasiveness Some virulent bacteria produce proteins that destroy cell membranes or stimulate phagocytosis of host cells. These virulence factors allow bacteria to enter the host's body through the layers of cells that come in contact with the pathogen, whether they are cells of the outer covers of plants or animals or layers of epithelium of internal organs.

VIRULENCE FACTORS 3. Colonization is the process of multiplication of microbes at the site of adhesion. Colonization provides the accumulation of microorganisms to such a critical concentration that can cause a pathological effect.

VIRULENCE FACTORS 4. Suppression of the immune response Many bacteria release virulence factors that inhibit the body's immune system. For example, bacteria secrete proteins that attach to host antibodies. Another type of substance that inhibits the immune response is the polysaccharide capsule surrounding the cell. These polysaccharides complicate phagocytosis of bacteria by specialized cells of the immune system (macrophages) and lymphocytes.

VIRULENCE FACTORS 5. Toxins Many virulence factors are proteins that the pathogen produces and then secretes into the environment and which causes damage to the host tissues. For example, with food poisoning it is the toxins that cause the symptoms of the disease.

BACTERIAL TOXINS

FORMS OF INFECTION PROCESSES Infectious disease Bacteriocarrier Ø Chronic (presence of pathogens for several months or even years) Ø Transitory (short-term (most often - once) excretion of the pathogen in the absence of clinical manifestations of the disease) Ø Sharp (a consequence of a recent illness)

COMMON ORAL INFECTIONS Gingivitis Dental Caries Periodontal Disease Canker Sores Oral Herpes

REASONS OF ORAL INFECTIONS Øinjuries Øa lack of vitamins and trace elements Øa general decrease in immunity Øallergic reactions Øinfections Øthe presence of tartar deposits Øpoor hygienic condition of the cavity

BIOLOGICAL RESEARCH METHODS Biological research methods are aimed at determining the presence of pathogen toxins in the test material and on the detection of the causative agent. Methods include infecting laboratory animals with the test material, followed by isolation of a pure pathogen culture or establishing the presence of a microbial toxin and its nature. The method is highly sensitive, can be used in the early stages of the disease, but is not always available, expensive, long-lasting, unsafe.

OBJECTIVES OF BIOLOGICAL METHOD 1. Diagnosis of infectious diseases. 2. Identification of pure culture. 3. Definition of virulence. 4. Isolation and identification of exotoxins. 5. Cultivation of viruses. 6. Reception of immunopreparations. 7. Checking the harmlessness and effectiveness of medications (including chemotherapy drugs, immunopreparations) and others.

STAGES OF BIOLOGICAL METHOD 1. Material intake. 2. Material processing. 3. The choice of a laboratory animal. 4. Infection of animals by one of the methods. 5. Registration of signs of illness of the infected animal or its death. 6. Intravital sampling of material from the animal and carrying out bacteriological and serological studies, setting an allergic test. 7. Autopsy, study of pathoanatomical and pathomorphological pattern. Preparation of smears-prints from internal organs. 8. Identification of the selected culture. 9. Conclusion on the results of the study.

TASK 1 STAINING BY BURRY-HINS METHOD The Burry-Hins method is used to color capsular bacteria and is based on the fact that the capsule does not perceive the dyes. The capsule is detected by negative contrasting backgrounds over the Burry. For this, black mascara is mixed into culture and dried. After that, for fixation in the flame of the burner, stain the bodies of microbial cells according to Hins – aqueous fuchsine for 1 minute and rinse with water for 5 -10 seconds. NB! As a result, a colorless capsule and red microbial bodies are clearly visible on a dark background.

TASK 1 STAINING BY BURRY-HINS METHOD Klebsiella pneumonia. A smear of pure culture. Burri-Hins staining

TASK 2 PETRI DISH WITH S. AUREUS INOCULATED ON BLOOD AGAR Hemolysis or haemolysis is the rupturing (lysis) of the red blood cells (erythrocytes) and the release of their contents (cytoplasm) into the surrounding fluid (e. g. blood plasma). Hemolysis may occur in vivo or in vitro (inside or outside the body). Hemolysins damage the host cytoplasmic membrane, causing cell lysis and death. The activity of these toxins is most easily observed with assays involving the lysis of the red blood cells (erythrocytes).

TASK 2 PETRI DISH WITH S. AUREUS INOCULATED ON BLOOD AGAR The pathogenic properties of staphylococci are due to the ability to produce exotoxins and enzymes of aggression. They cause lysis of erythrocytes, have a lethal and necrotic effect. The most studied hemolytic properties of toxins, so they are often called hemolysins. The hemolytic ability of staphylococci can be determined by sowing on blood agar, in which 18 -24 hours around the staphylococcus colony, the hemolysis zone is visible.

TASK 2 PETRI DISH WITH S. AUREUS INOCULATED ON BLOOD AGAR 3 2 1 1 – Staphylococcus colonies 2 – Hemolysis zones 3 – Blood agar

TASK 3 TEST TUBES WITH NORMAL RABIT PLASMA AND WITH S. AUREUS PLAQUE Plasma-coagulant activity of the culture is checked by inoculation in tubes with 0. 5 ml of citrated rabbit plasma at a dilution of 1: 4. Pathogenic staphylococci coagulate the plasma for 2 -24 h under the conditions of a thermostat. Accounting is performed after 24 hours by the formation of a small jelly-like clot on the bottom of the tube.

TASK 3 TEST TUBES WITH NORMAL RABIT PLASMA AND WITH S. AUREUS PLAQUE Plasmacoagulase positive Plasmacoagulase negative

TASK 4 S- AND R-FORMS OF COLONIES S-form Ø Round Ø Smooth Ø Even edges Ø Shiny surface R-form Ø Irregular in shape Ø Rough Ø Serrated edges