Infectious Agents Flashcards
How are microbes visualised?
Bacteria, fungi, protozoa, and helminths
- can be seen using light microscope (x400 to x 1000)
Viruses seen via EM x40,000
How does bacterial growth occur?
Via binary fission with each doubling taking 20-30 mins at optimum of 35-37 ℃
Describe the structure of a virus
20-300um
DNA/RNA genome
Linear, segmented, single or dsGenomes of varying sizes 9kb - 300kb
Have nucleocapsid (protein core)
No cytoplasm
(non)Enveloped
May have host component on viral membrane
What is the Linnean classification system?
Domain Kingdom Phylum Class Order Family Genus Species
What is required for bacterial growth?
- Carbon, water, nitrogen
- nutrients & minerals
- correct osmotic pressure
- correct pH
- correct Temperature
- correct atmosphere
Describe the key features of protozoa
- single cells
- 5-300 um
- single / multiple nuclei
- trophozites, cysts, and othe rmorphocytes have complex
life cycles - Haploid DNA
- Morphology varies throughout life cycle
- can have flagella
How are different virus’ classified?
Viruses can be classified based on their protein nucleocapsid structure
- helical
- cubic
- complex arrangement
Describe the Ebola virus
Enveloped RNA virus with a very complex nucleocapsid part of the filoviridae family
What criteria is used to classify pathogenic organism?
- Structural, functional and metabolic observations
- Molecule and genetic / genome analysis
What are helminths?
Multicellular parasitic worms
Describe the key features of Bacteria
- 1/1000th of a mm
- 0.5 - 3um
- Prokaryotic
- Haploid DNA
- Circular genome
- no nucleus
- no mitochondria
- undergoes binary fission
- usually has rigid cell wall outside cytoplasmic membrane
What is the significance of pathogenic organism classification?
Identification is essential to understand the (micro)biology, evolution & phylogenetics, pathogenesis of infectious diseases, life cycles, diagnosis, effective treatment and public health control of infectious diseases
What are parasites?
Organisms that live in an organism of another species (host) and benefits by deriving nutrients at the other’s expense
What is the difference in the movement of motile and non motile bacteria?
Motile bacteria with flagella move rapidly
Non motile bacteria move ‘on the spot’
Compare and contrast prokaryotes and eukaryotes
Prokaryotes e.g. bacteria
- No nucleus
- no mitochondria
- mainly circular DNA
Eukaryotes
- chromosomes
- nucleus
- membrane bound organelles
Describe structural features of helminths
- Have different morphologies and sizes at different
stages of their life cycles - Can be microscopic or visible to the eye
What technique is used to distinguish between bacterial species?
Gram staining bacteria
stains include:
- iodine, alcohol, safranin
Where do virus’ replicate?
Virus’ are obligate intracellular organisms so can only replicate inside host cells
What are the biological characteristics of the 4 microbes?
All organisms are cells except viruses - don’t have membranes
Cell life cycles, cellular and genome organisation
Parasites are multi-cellular
Name 3 examples of Fungi / their infections caused
Superficial mucosa
- skin, nail, hair & mucosal membranes (dermatophytes) or
thrush
Cutaneous - Tanea (ringworm)
Systemic muycoses e.g. histoplasmosis
What are the 3 groups of helminths?
Cestode - tapeworms e.g. taenia, saginata (beef
tapeworm)
Trematode - flatworms or flukes including: schistoma
haematobium
-> cause of bilharzia / schistosomiasis
Nematodes - roundworms e.g. Ascaris lumbricoides
Compare the 4 types of microbes with each other
Parasites are more complex than viruses
Viruses are tiny in comparison to bacteria and protozoa
Bacteria are x10 or x100 smaller compared to animal / plant cells
Light microscopes used to see bacteria
Electron microscope used to see viruses
Outline the life cycle of a virus
- Attachment - virus attaches to target cell
- Penetration - cell engulfs virus via endocytosis
- Uncoating - viral contents released
- Biosynthesis - viral RNA enters nucleus, replicated by
viral RNA Pol - Assembly - New phage particles made and released
into extracellular fluid - cell continues new virus
production
Describe the structure of the Influenza Virus
Influenza virus is an enveloped virus with surface haemaglutinin
What is fungi classification based on?
Fungi classification is complex and based on morphology, reproduction mode (Sexual/asexual) and disease caused
It’s easier to consider fungi by type of infection
What are the 4 major microbe types?
Viruses
Bacteria
Fungi
Parasites
Describe the structural features of fungi
- over 2um
- eukaryotic
- can be single or multi-cellular
- Haploid or diploid
- single or multiple nuclei
- rigid chitinous cell wall
Describe the features of Adenovirus
Adenovirus is an example of non-enveloped DNA virus usually associated with conjunctivitis
Give examples of the different structures of fungi
Yeast
spheroid single cells budding and dividing
Filamentous forms / moulds
hyphae
multi-nucleating branching hyphae form mycelium
Describe anaerobic bacteria growth and visualisation
anaerobic bacteria only grow in absence of O2
Gram +ve, rod like spores forming
How are microbes classified?
Based on:
- size
- biological complexity
- life cycles
- prokaryotes / eukaryotes
- haploid / diploid
- genomes and genetics
