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Bacterial disease

Bacterial disease. Pathogen and the host. Pathogens. Pathogenic bacteria are capable of causing disease Infectious disease – change of structure or function of a host caused by microbes This change is manifested with a set of symtoms (pain, fever, redness, swelling). Infection.

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Bacterial disease

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  1. Bacterial disease Pathogen and the host

  2. Pathogens • Pathogenic bacteria are capable of causing disease • Infectious disease – change of structure or function of a host caused by microbes • This change is manifested with a set of symtoms (pain, fever, redness, swelling)

  3. Infection • The establisment and multiplication of bacteria on the site in the host • Systemic - bacteria are spread throughout the body • Sepsis - the presence of bacteria or their products in the blood or tissues • Septicemia -the multiplication of bacteria in the blood • Toxemia- the presence of a bacterial toxin in the blood

  4. Infection II • Asymptomatic carriage – patogens are present without the production of any symptoms • Clononization – the establishment and multiplication of bacteria on a site (mucuse membranes) of thehost

  5. Virulence factors of pathogens • The features of bacteria that alow them to: • invade and remain with the host, • acquire nutrients, • avoid or demage the host immune system • spread between hosts

  6. Pathogenicity • Thrue pathogens (B.anthracis) are capable of infecting healthy hosts • Oportunistic pathogens (Pseudomonas aeruginosa) are capable of infecting hosts which are damaged (immunocompromised by another infection)

  7. Normal flora or commensals • Presence in the body is normally beneficial to the host • Resident microflora on a site in the host gastrointestinal tract genito-urinary tract (vagina) respiratory tract skin

  8. The nature of bacterial disease • Bacillus athracis was proven to be a causative agent for anthrax (1870 Robert Koch) • The etiologies (causes) of many diseases in animal were shown to be a result of bacterial infection

  9. The nature of bacterial disease • The symptoms of the disease depen on the site of infection, toxic products of pathogens and the abbility of the host to combat the immune system • Disease may be acute or chronic or asymptomatic

  10. The nature of bacterial disease • Bacteria are capable of cuaisng: • 1) just one kind of diseases as swine dysentery (Brachispira hyodysenteriae) • 2) range of different diseases in many host species (Staphylococcus aureus)

  11. Koch´postulates • How to identify the causative agent and establish how it causes disease • The relationship between a bacterium and a observed disease has been established if the candidate bacterium fulfils all criteria laid down by Robert Koch

  12. Koch´postulates • 1.The bacteria should be foound in all cases and at all sites of the disease • 2. The bacteria should be isolated from the infected host and mantained in pure culture

  13. Koch´postulates • 3)The pure culture microbe should cause symptoms of the disease on on inoculation into a susceptible individual (animal model) • 4)The bacteria shoul be reisolated from the intentionaly infected host

  14. Entry and colonization of animal hosts

  15. Overview • Bacterium must reach the site at wich it can survive, accumulate nutrents to allow it to replicate

  16. Transmission between hosts • Air/aerosols • Food/water borne • Direct contact • Sexual transmission • Vectore –borne (Borrelia sp.) • Microbes may remain on surfaces or penetrate throught into the tissues

  17. Colonization of surfaces • Adhesion – adhesion molecules on the surface of the host cells bind to the microbial adhesins (proteins, polysachrides ..) • Motility and mucinases break down mucous

  18. Invasion of host cells • Invasins induce non-phagocytic cells to také up bacteria • Intracellular parasites • Possibility to penetrate throught epitelial layers and to spread within the host

  19. Acquisition of nutrients • For example iron –chelating proteins (siderofors) alow the bacteria to compete with the host for iron (in lactoferin) • Salmonella Typhimurim • Listeria monocytogenes

  20. Spread of bacteria • Extracellular enzymes and toxins which destroy host tissue alow the dissemination of the pathogen in the host • hyaluronidase (S. aureus)

  21. Avoidance of host defense mechanisms • Phagocytes • listeriolysin O (L. monocytogenes) breaks down the phagosome membranes allowin the bacteria to escape into the cytoplasm • Antibodies • Protein A (S.aureus) • Sialic acid in capsules not recognised as foregin

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