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Flashcards in Microbes and medicine Deck (23)
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opportunistic pathogens

microbes that are not normally pathogenic, but when the immune system is compromised will colonise the body


6 examples of medically important pathogens

  • Viruses- H1N1
  • Fungi- Trichophyton
  • Prions-Kuru
  • Protozoa- plasmodium
  • Helminths- ancylostoma duodenale
  • Bacteria- bacillus antracis


koch's postulates description and 4 rules

  • Guidelines used to demonstrate that a specific pathogen causes specific disease symptoms

  1. The pathogen must be present in every individual with the disease
  2. A sample of the microorganism taken from the diseased host can be grown in pure culture
  3. A sample of the pure culture causes the same disease when injected into a healthy host
  4. The microorganism can be recovered from the experimentally infected host


exceptions to koch's postulates

  1. Microbes that can't be cultured in lab (i.e Treponema pallidum)
  2. Pathogens that also can be found in healthy subjects (i.e Vibrio cholera)
  3. Some diseases are caused by multiple pathogens


8 bacterial virulence factors

  1. Adhesins- bind to host cells e.g. Neisseria gonorrhoeae, Neisseria Meningitidis
  2. Motility- move through mucus e.g. helicobacter pylori (stomach ulcers)
  3. Internalin-related proteins (InlB) e.g. listeria monocytogenes
  4. Siderophores- bind to iron and rip it away from haemoglobin e.g. Yesinia pestis
  5. Capsules- avoid phagocytosis
  6. Cellular enzymes- destroy host cell chemicals
  7. Endotoxins- cause inflammation
  8. Exotoxins- can be fatal


gram positive vs negative

Gram positive bacteria

  • Produce exotoxins
  • Thick peptidoglycan layer

Gram negative bacteria

  • Can produce both exotoxins and endotoxins
  • Thin peptidoglycan layer and outer membrane


exotoxin definition and 3 examples

toxins that are produced in pathogen and released into surrounding medium

  1. Cytotoxin (Steptolysin) produced by the bacteria such as Staphylococcus pyrogenes which cause the complete lysis of red blood cells (beta haemolysis)- cytotoxins destroy cells and take in all of the nutrients
  2. Neurotoxin (botulinum) produced by the bacteria such Clostridium botulinum which cause paralysis
  3. Enterotoxin (Shiga toxin) produced by the bacteria Shigella dysenteriae causes severe dysentery


selective toxicity

kills microbes but spares host living cells through targeting microbe specific elements


bacterial cell components targeted by different types of antibiotic

  1. Inhibition of cell wall synthesis
    • Penicillin
  2. Inhibition of protein synthesis
    • Aminoglycosides
  3. Disruption of cytoplasmic membrane
    • Polymyxins
  4. Inhibition of general metabolic pathway
    • Sulfonamides
  5. Inhibition of DNA or RNA synthesis
    • actinomycin


how does bacterial resistance develop

  1. A proportion of the bacterial population gain resistance to antibiotic via mutation; or through transformation, transduction or conjugation from another resistant bacteria
  2. Bacteria with resistance survives antibiotic
  3. Bacteria with resistance multiply, and pass on the resistant trait- use of the antibiotic therefore selects for the antibiotic resistance gene
  4. Resistant bacterial population survives subsequent encounters


how to reduce bacterial resistance

  • Decrease antibiotic utilisation
  • Improve diagnostics
  • Identify new targets
  • Combination therapies


penicillin mode of action and problems

  • Antibiotic that disrupts the peptidoglycan layer, through targeting the enzyme that crosslinks the short peptide bonds between the NAM and NAG subunits
  • Beta-lactamase enzyme cleaves the beta-lactam ring on penicillin, so penicillin no longer works


common sources of infectious agents

  • Animals, humans, fomite, food, water


Common modes of transmission of infectious agents

  • Contact, airborne, vector


5 stages of infectious disease

  1. Incubation period- bacteria has attached, no signs or symptoms
  2. Prodromal period- vague general symptoms, not every disease has a prodromal period
  3. Illness- most severe signs and symptoms, and usually most infectious stage
  4. Decline- declining signs and symptoms
  5. Convalescence- no signs or symptoms



the amount of a particular disease that is usually present in a community is referred to as the baseline or endemic level (or particular to that specific area)



an increase, often sudden, in the number of cases of a disease above what is normally expected in that population in that area



an epidemic that has spread over several countries or continents and usually affecting a large number of people



the incidence of death in a population



refers to the incidence of disease including fatal and non-fatal disease



the number of new cases of the disease in a given period of time



the totally number new and existing cases in a population over time


epidemiology study steps

  1. Reporting clinical cases-attending hospital or medical practices
  2. Diagnostic follow up to confirm disease and incidence/prevalence
  3. Monitor disease incidence following therapy/vaccination
  4. Monitor case histories/patient records