6.1 Basis of Infection Flashcards
What are the four types of prokaryotes?
Saprophyte
Symbiont
Commensal
Pathogen/Parasite
What is a saprophyte?
An organism that feeds on dead and decaying organic matter.
What is a symbiont?
An organism that lives in collaboration with another organism with mutual benefit.
What is a commensal?
An organism which lives in associaion with another organism without adversely affecting the host (indirect benefit of keeping pathogens out)
What is a pathogen?
Organisms which live as parasites on or in another organism to the detriment of the host.
What is a primary pathogen?
Obligate pathogen - infection always associated with disease.
What is a secondary pathogen?
Opportunistic pathogen - can be found in healthy individuals, waiting for the opportunity to infect and cause disease.
What are the five possible routes of infection?
Direct contact Aerosol Oro-faecal Transplacental Vector-borne
What are the two possible sites of infection?
Exogenous - epithelial surfaces
Endogenous - body tissues (intracellular, extracellular, vesicular)
What are the five cells of the immune system?
Neutrophils - phagocytosis
Monocytes/macrophages - phagocytosis
Eosinophils - kill parasites
Basophils/mast cells - kills parasites
Lymphocytes - anti-viral and aid other cells
How do we identify a pathogen is responsible for a disease?
Koch’s Postulates
- pathogen present in every case of the disease
- pathogen isolated from disease host and grown in pure culture
- disease is reproduced when pure culture inoculated in healthy host
- pathogen recoverable from experimentally infected host
What are the five types of pathogens?
Prions Viruses Bacteria Fungi Parasites
What is a prion?
‘infectious protein’ - misfolded protein that induces a conformational change in normal prion protein of a host.
What is a virus?
Obligate intracellular parasite
Describe the basic structure of a non-enveloped virus
Nucleic acid
Capsid
Describe the basic structure of an enveloped virus
Nucleic acid
Capsid
Envelope - glycoproteins and host-derived membrane.
How is immunity to viruses provided?
Neutralising antibody (produced by B lymohocytes) Killer T lymphocytes
How are viral infections treated?
Vaccinations for prevention
Anti-viral drugs
Biosecurity for prevention
Describe the basic structure of bacteria.
Capsule Cell wall DNA coil Flagellum Ribosomes Plasmid Cytoplasm Plasma membrane Pili Cytoplasmic inclusion
What are the differences between gram-positive and gram-negative bacteria?
Gram-negative: surrounded by thin peptidoglycan cell wall and lipopolysaccharide membrane.
Gram-positive: No outer membrane but layers of peptidoglycan.
What is the life cycle of bacteria/fungi?
1- colonisation
2- invasion
3- replication
4- dissemination
Describe different methods of pathogenesis of bacteria.
Invasive bacteria - localised or systemic infection.
Endotoxigenic bacteria - degradation products released into bloodstream.
Exotoxigenic bacteria - toxin secreted.
How does the immune system fight bacterial and fungal infection?
Phagocytosis
Complement activation
Opsonising antibody
How are bacterial and fungal infections treated?
Antimicrobial drugs
Antifungal drugs
What are the types of parasites?
Endoparasites
Ectoparasites
what are endoparasites?
Helminths (worms)
Protozoa (single celled eukaryotes)
What are ectoparasites?
Arthropods (insects)
How does the immune system respond to parasites?
IgE antibodies
Eosinophils
Basophils/Mast cells
How are parasite infections treated?
Specific anthelmintics, ectoparasiticides, anti-protozoal drugs
