Module 4 - Microbes as Pathogens Flashcards
Name 4 key ways in which the microbiota help in defence against pathogens
- Cover every surface so less room for pathogens
- Some produce antibiotics
- Compete with pathogens for resources
- Role in digestion + help immune system
Name the three areas of the human body where most microbiota are found
- GI Tract
- Skin
- Mouth/nasopharynx
How is the gut microbiota initially acquired?
On passage through the birth canal
What change marks the transition to a more stable adult gut microbiota
The introduction of solid food
What is the only significant normal flora bacteria? (And what ailment is more common in people who have this?)
Heliobacter pylori (gastric ulcer)
What type of bacteria are most common in the colon (in terms of oxygen requirements)
Obligate anaerobes
What difference was found between normal mice and “germ free” mice with no microbiota?
Normal mice consume less food, but have 42% MORE body fat (better absorption)
What is dysbiosis?
A disruption of the normal gut flora, which is associated with disease
Name the opportunistic pathogen which is found in the soil and can affect burn patients
Pseudomonas aeuginosa
Name the opportunistic pathogen which can colonise intraveous catheters
Staphylococcus epidermidis
Name the opportunistic pathogen which causes meningitis, and where it is normally found
Neisseria meningitidis -> nasopharynx
What key symptom does Mycrobacterium tuberculosis (TB) cause in the body?
Ghon complexes (granulomas of caseous necrotic tissue, including dead and dying macrophages)
Describe the structure of Treopnema pallidum, the disease they cause and the three phases of the disease
Flexible, helical bacteria; syphilis; Primary lesion, secondary (spread) and latent phase
Name the 4 steps of Koch’s Postulates (and what this actually means)
Way to prove that a particular microbe causes a particular disease:
1. Organism found in lesion
2. Grow organism outside the body in lab
3. Organism must reproduce the disease
4. Re-isolate from test animal
Name three examples of problems with carrying out Koch’s Postulates
- Cannot grow cultures in lab media for some microbes (e.g., Mycbacterium leprae)
- Ethical problems (e.g., AIDS, Ebola)
- No suitable animal model, e.g., gonorrhoea)
What are the two metrics by which virulence can be measured?
Minimum infectious dose and LD50
Name two examples of virulence determinants in some bacteria
Capsule (often poly-D-glutamic acid) to inhibit phagocytosis
Toxins (suppress initially, then lethal)
Name the 4 stages of the infection process
Exposure - Adherence - Invasion - Multiplication
Name the 2(3?) stages of the disease process
Toxicity//Invasiveness -> Tissue or Systemic Damage
What is the difference between how commensal and pathogenic E. coli adhere to the host?
Commensal: attach by Type 1 peritrichous fimbriae (carrying a protein H tip adhesin) to mannose receptors on epithelial cells
Pathogenic: use CFA (colonisation factor antigen) fimbriae to attach to duodenal mucosa and release toxins
Give an example of non-fimbrial adhesion (species and mechanism)
S. pyogenes -> binds to respiratory tract epithelial cells using M PROTEIN (causes sore throat + rheumatic fever)
What is the difference between localised and systemic infection?
Systemic - gets into bloodstream
Localised - only affects one organ or body part
What are toxins (basic defintion)?
Simple soluble proteins (often enzymes) which are extracellular, rapidly transported in the body, and cause damage to the host
Name and give one example of the 3 main types of exotoxins
Enterotoxin (e.g., cholera toxin)
Cytotoxin (e.g., haemolysin of C. perfringens)
Neurotoxin (e.g., botulinium toxin)
What do enterotoxins do?
Stimulate GI tract cells in an abnormal way, eliciting profuse fluid secretion (dehydration)
What do Cytotoxins do?
Kill cells by enzymatic attack
What are the two main types of cytotoxins?
1 - Those that bind to cholestrol in membranes of host cells, forming pores -> ß-haemolysis
2 - Phospholipase enzymes
What do neurotoxins do?
Interfere with normal transmission of nerve impulses
What is the structure and function of the botulinum toxin?
A-B toxin (heavy and a light chain linked by disulphide bond) -> heavy chain binds to glycoprotein receptor on neurons, so light chain (A) can enter nerve cell
How does botulinum toxin cause flaccid paralysis?
Light chain Zinc Metalloprotease inhibits release of neurotransmitter Acetylcholine, preventing muscle contraction
What enzyme does the cholera toxin activate inside the cell (and how does this lead to fluid loss)?
Epithelial adenylate cyclase, blocks Na+ movement -> water movement into lumen
What are Endotoxins (and what is the main example)?
Heat-stable lipopolysaccharides embedded in the outer membrane of Gram-negative bacteria (LIPID A)
What are the three main effects of Lipid A (and what symptoms do these cause)?
- Activates Monocytes -> fever
- Activates Complement Cascade -> permeabilisiation of blood vessels
- Activates coagulation cascade -> vascular coagulation
What structural element of Lipid A can vary (and how does this affect its toxicity)?
The length and number of fatty acyl chains (more and shorter = higher toxicity)
How does Lipid A actually spread in the host?
Vesicles containing Lipid A “bleb” off from bacteria into host tissue and shed into bloodstream
Name 4 modes of transmission for viral diseases (and most common one?)
Inhalation (MOST COMMON); ingestion; inoculation; congenital
Name 4 modes of laboratory diagnosis of viral diseases (and least viable for population-wide)
Whole virus (least viable); viral antigen, viral nucleic acid; specific antibody response
State the structure and genome type of the Picornavirus family (e.g. HepA)
Small, ssRNA, icosahedral, naked viruses
Name the 4 genuses of Picornavirus (and the most common syndrome of each)
Enterovirus (CNS e.g., polio)
Hepatovirus (HepA)
Rhinovirus (Colds)
Aphthovirus (Foot and Mouth)
State how Polio is spread + symptoms
Faecal-oral route; generic symptoms (BUT 5% flaccid paralysis)
State the structure and genotype of Orthomyxoviruses (and most significant example)
ssRNA, enveloped (influenza)
Name two examples of antiflu drugs that block virus exit from cells
Tamiflu and Relenza
State the structure and genome type of Herpesviridae Family (and name 3 subfamilies)
Icosahedral, Enveloped, dsDNA viruses (Alphaherpesviridae, Betaherpesviridae, Gammaherpesviridae)
What is the common distinguishing feature of Alphaherpesviridae (and what molecule has been implicated in this feature)?
Latency and Reactivation (cortisol/stress)
What drug can be used to treat HSV1/Herpes Simplex Virus 1 (and what stage of the viral life cycle does it inhibit)?
Acyclovir (ACV) - blocks viral DNA synthesis
Name the structure + genome type of Paramyxoviruses (and two main examples)
Helical, Enveloped, ssRNA (Measles and Mumps)
State structure + genome type of Togaviridae (and main example)
Enveloped, ssRNA (Rubella -> Congenital)
State structure and genome type of Papovaviridae (Papilloma viruses), and main symptom
Icosahedral, dsDNA (cause warts which can be oncogenic)
What family does Ebola belong to (and structure + genome type)?
Filoviridae (ssRNA)
Name the three factors in the disease triangle
Pathogen/Susceptible Host/Favourable Environment for Pathogen
Name the fungus that caused the potato blight in 1840s Ireland
Phytophthera infestans
Name the 5 stages of causing disease in plants
- Pathogen must recognise the host
- Penetrate host barriers
- Suppress host defence systems
- Move (invade) through host tissues
- Utilise host components for growth and reproduction (nutrition)
Name 3 virulence factors produced by plant pathogens
Enzymes (penetration, movement within host, breakdown of large molecules), Toxins (interfere with host cell functions in advance of pathogen), Growth Regulators
Why can the influenza virus mutate so quickly?
It can undergo ANTIGENIC SHIFT when the RNA segments of two different strains undergo reassortment in the host
What is the structure + genome type of Adenoviruses?
Icosahedral, dsDNA viruses (diameter 80nm)
Full name, Structure + Genome of CTV?
Citrus Tristeza Virus -> +ssRNA; flexous rod, helical symmetry
Name the vector that spreads CTV, and how it spreads in the plant
Brown citrus aphid, phloem
Full name, structure + Genome of TMV
Tobacco mosaic virus; +ssRNA, helical
Symptoms of CTV in plants?
Clear veins which turn corky, chlorosis followed by leaf cupping, die back
Symptoms of TMV?
Chlorosis; Mosaic-like Mottling on Leaves; Rugosity -> stunted growth, lower yields
Which virulence factors can cause soft rots in plants?
Enzymes such as Pectinases, proteases, cellulases (which degrade cell walls)
Name the genus of bacteria which causes Crown Gall Tumours
Agrobacterium (tumifacens)
How does Agrobacterium cause Crown Gall Tumours?
Enters the plant through wounds -> transfers its own DNA (T-DNA) into plant genome -> upregulates plant hormones auxin and cytokinin
Name the bacterium which has been used as a biocontrol agent against insects (also its Gram ID and the toxin it produces)
Bacillus thuringiensis (Gram +ve rod) -> Bt toxin
Why is the Bt toxin insect-specific?
It is highly insoluble in normal conditions - only soluble in high pH (alkaline) conditions of insect gut, where it forms pores in gut wall
Name the fungal species which is known as Greenguard and used as a biocontrol agent
Metarhizium sp.
Name two other fungal species besides Greenguard which are used as biopesticides
Entomophthorales (Zygomycetes) and Beuvaria bassiana (thrips, mealy bugs, weevils, white fly aphids)
Name a species of Nematode-trapping fungi
Arthrobotrys
