The doctrine about infection. Pathogenicity and virulence of bacteria.

1. Medical biology, microbiology, virology, immunology department The doctrine about infection. Pathogenicity and virulence of bacteria. by as. O.V. Pokryshko

2. The interaction of the susceptible human organism and the pathogenic microorganism in certain conditions of the external and social environment which gives rise to an obvious or latent pathological process is called an infectious process.

3. Main Features of PathogenicMicroorganisms. Pathogenicity.This is the potential capacity of certain species of microbes to cause an infectious process. Virulencesignifies the degree of pathogenicity of the given culture (strain). Virulence, therefore, is an index of the qualitative individual nature of the pathogenic microorganism. Virulence in pathogenic microbes changes under the influence of natural conditions.

4. The virulence of pathogenic microorganisms is associated with • adherence, • invasiveness, • capsule production, • toxin production, • aggressiveness • and other factors.

5. The adherence

7. Adherence bacteria to cell surfaces

9. Adherence of vibrio cholera on the mucose

10. Capsule production Capsule production makes the microbes resistant tophagocytosis and antibodies, and increases their invasive properties. Thus, for example, capsular anthrax bacilli are not subject to phagocytosis, while noncapsular variants are easily phagocytized.

11. The role of capsular material in bacterial virulence. Some pathogenic microorganisms (B. anthracis, C. perfringens, S. pneumo-niae, causative agents of plague and tularaemia) are capable of producing a capsule in animal and human bodies. Certain microorganisms produce capsules in the organism as well as in nutrient media (causative agents of rhinoscleroma, ozaena, pneumonia).

12. Invasive propertiesof pathogenic bacteria • Virulent microbes are characterized bythe ability to penetrate tissues of the infected organism (invasive properties). • collagenase and hyaluronidase • immunoglobulin A protease • leukocidins • M-protein • protein A

13. Collagenase and hyaluronidase degrade collagen and hyaluronic acid, respectively, thereby allowing the bacteria to spread through subcutaneus tissue (Streptococci, Staphylococci, Clostridium). Immunoglobulin A protease degrades IgA, allowing the organism to adhere to mucous membranes, and is produseed chiefly by N. gonorrhoeae, Haemophilus influenzae, and S. pneumoniae.

14. Leukocidins can destroy both neutrophilic leukocytes and macrophages. M-protein of S. pyogenes is antiphagocytic. Protein A of S. aureus binds to IgG and prevents the activation of complement.

15. Coagulase, which is produced by S. aureus and accelerate the formation of a fibrin clot from its precursor, fibrinogen (this clot may protect the bacteria from phagocytosis by walling off the infected area and by coating the organisms with a layer of fibrin)

17. The invasion of cells by bacteria

18. Toxin production According to the nature of production, microbial toxins are subdivided into exotoxins and endotoxins. More than 50 protein exotoxins of bacteria are known to date.

19. Exotoxins easily diffuse from the cell into the surrounding nutrient medium. • They are characterized by a markedly distinct toxicity, and act on the susceptible organism in very small doses. • Exotoxins have the properties of enzymes hydrolysing vitally important components of the cells of tissues and organs.

20. Exotoxinsexert their effects in a variety of ways – by inhibition of protein synthesis, inhibition of nerve synapse function, disruption of membrane trans-port, damage to plasma membranes.

21. Exotoxins may be devided into fifth categories on the basis of the site affected: • neurotoxins(tetanotoxin, botulotoxin) C. tetani, C. botulinum, B. cereus, S. aureus; • cytotoxins(enterotoxins, dermatonecrotoxin)E. coli, Salmonella spp., Klebsiella spp., V. cholerae, C. perfringens; • functional blocators(cholerogen),V. cholerae; • membranotoxins(hemolysins, leucocidin),S. aureus; • exfoliatinS. aureus.

22. Action of the hemolysin on red blood cells

23. MICROORGANISM TOXIN DISEASE ACTION Clostridium botulinum Several neurotoxins Botulism Paralysis; blocks neural transmission Clostridium tetani Neurotoxin Tetanus Spastic paralysis; interferes with motor neurons Corynebacterium diphtheriae Cytotoxin Diphtheria Blocks protein synthesis Bordetella pertussis Pertussis toxin Whooping cough Blocks G proteins that are involved in regulation of cell pathways Streptococcus pyogenes Hemolysin Scarlet fever Food Lysis of blood cells Staphylococcus aureus Enterotoxin Poisoning Intestinal inflammation Aspergillus flavus Cytotoxin Aflatoxicosis Blocks transcription of DNA, thereby stopping protein synthesis Amanita phalloides Cytotoxin Mushroom foodpoisoning Blocks transcription of DNA,thereby stopping protein synthesis

26. Endotoxins • are more firmly • bound with the body of the bacterial cell, • are less toxic and act on the organism in large doses; • their latent period is usually estimated in hours, • the selective action is poorly expressed.

27. According to chemical structure, endotoxins are related to glucoside-lipid and polysaccharide compounds or phospholipid-protein complexes. They are thermostable. Some endotoxins withstand boiling and autoclaving at 120°C for 30 minutes.

29. Action of the endotoxin Endotoxin in the bloodstream

30. Differences between exotoxins and endotoxins

32. In characterizing pathogenic microbes a unit of virulence has been established. • Dlm (Dosis letalis minima), representing the minimum amount of live microbes which in a certain period of time bring about 95-97 %death of the corresponding laboratory animals. • the absolute lethal dose of pathogenic microbe Dcl (Dosis certa letalis) which will kill 100 % of the experimental animals has been established. • At present LD50 (the dose which is lethal to one half of the infected animals) is considered to be the most suitable, and may serve as an objective criterion for comparison with other units of virulence.

33. The terminfection (L. infectio to infect) signifies the sum of biological processes which take place in the macroorganism upon the penetration of pathogenic microorganisms into it.

34. Infectious disease designates one of the extreme degrees of manifestation of the infectious process. Infectious diseases are considered to be phenomena including biological and social factors.

35. Infectious diseasesdiffer from other diseases in that • they are caused by live causative agents of a plant and animal origin • and are contagious, • the presence of a latent period, • specific reactions of the body to the causative agent • and production of immunity

36. Koch’s postulates. For the origination and development of the infectious process three conditions are necessary: 1.the presence of pathogenic microbe, 2.its penetration in to a susceptible macroorganism, 3.certain environmental conditions in which the interaction between the microorganism and macroorganism takes place.

37. What is an Epidemic? The occurrence of more cases of disease than expected in a given area or among a specific group of people over a particular period of time*. Epidemic

38. What is a Pandemic? An epidemic occurring over a very wide area (several countries or continents) and usually affecting a large proportion of the population. Examples: • Cholera • AIDS • Pandemic Influenza Pandemic

39. Source of infection:Sick menSickanimalCarrier Transmission factor:infected food, water, dirtyhands, flies, fomites. Vectorsof pathogenicmicroorganims: ticks, louses, fleasmosquitos.

40. Routes of diseases transmission • There are various modes which pathogens are transmitted from a source to a susceptible individual. • airborne transmission • foodborne transmission • sexual transmission • direct contact transmission • parenteral route

42. Respiratory tract and airborne transmission. Airborne transmission occurs when pathogenic microorganisms are transferred from an infected to a susceptible individual via the air. Droplets regularly become airborne during normal breathing, but the coughing and sneezing associated with respiratory tract infections are primarily responsible for the spread of pathogens in aerosols and thus the airborne transmission of disease.

43. High-speed photograph of an aerosol generated by an unstifled sneeze.

44. Gastrointestinal tract—water and foodborne transmission. Microorganisms routinely enter the gastrointestinal tract in association with ingested food and water. Waterborne and foodborne pathogens can infect the digestive system and cause gastrointestinal symptoms.

45. Genitourinary tract – sexual transmission. The genitourinary tract provides the portal of entry for pathogens that are directly transmitted during sexual intercourse. Such infections are known as venereal or sexu- ally transmitted diseases.

46. Superficial body tissues – direct contact transmission. In some cases the deposition of pathogenic microorganisms on the skin surface can lead to an infectious disease. Since they require direct contact between skin and microorganisms for transmission to occur, these diseases are called contact diseases. Some diseases transmitted in this manner are superficial skin infections.

47. Parenteral route. Punctures, injections, bites, cuts, wounds, surgical incisions, and cracking skin due to swelling or drying establish portals of entry to a host for a potential pathogen. Such access is called the parenteral route (from Greek para [beside] and enterik [intestinal tract]. Microorganisms thus gain entry to the body by being deposited directly into the tissues beneath the skin or into the mucous membrane.

48. Portals of entry. • The routes of entry are • the respiratory tract, • gastrotestinal tract, • genitourinary tract, • skin, and wounds. The invasive properties of specific pathogens permit them to penetrate the body's defense mechanisms through a specific portal of entry. Most pathogenic microorganisms will cause disease only if they enter the body via this specific route.