Infectious Agents Flashcards
List some differences between prokaryotic and eukaryotic organisms.
EUKARYOTIC:
- contains a chromosome
- has a nucleus
PROKARYOTIC:
- no nucleus
- no mitochondria
- mainly circular DNA (plasmids)
Describe the structure of a virus.
- has a protein nucleocapsid (individual capsomeres in a helical, cubic or complex arrangement)
- no cytoplasm
- it may be enveloped or non-enveloped (may have components derived from the host cell)
- it is an obligate intracellular organism (meaning it can only replicate inside host cells)
- they have receptors on the nucleocapsid that allow it to bind to cells
Describe the structure of bacteria.
- prokaryotic
- contains haploid DNA as a circular genome
- has no nucleus
- usually have a rigid cell wall outside the cytoplasmic membrane (which retains the osmotic potential)
- has no mitochondria
- divides by binary fission
How does the Gram stain help us identify different bacteria?
The Gram stain divides bacteria into:
GRAM-POSITIVE - blue/purple
GRAM-NEGATIVE - red
These bacteria have differing cell wall structures which accounts for the different staining properties.
Describe becterial growth and list some of its requirments.
Bacterial growth occurs through binary fission. Their doubling time is approximately 20-30 minutes.
Their growth requires:
- carbon, water and nitrogen
- nutrients and minerals
- the correct pH
- the correct osmotic pressure
- the correct temperature
- the correct atmosphere
Describe the different classifications of bacteria based on their growth in different atmospheres (ie. O2).
There are two classes: Aerobes and Anaerobes.
Of the aerobes, we have:
- Strict aerobes: which will grow only in O2
- Facultative aerobes: which can grow in both atmospheres
Of the anaerobes, we have:
- Strict (obligate) anaerobes: which will grow only in the absence of oxygen
- Microaerophilic anaerobes: which grow best with small traces of oxygen
Describe the structure of fungi (mycoses).
- eukaryotic
- have haploid or diploid DNA
- have single or multiple nuclei
- have a rigid CHITINOUS cell wall outside the cytoplasm
- they can be single or multicellular
They come in two forms:
YEAST: spheroid single cells budding and dividing
FILAMENTOUS FORM/ MOULDS: multinucleate branching hyphae forming mycelium
What is the simplest way to classify fungi?
The classification of fungi is complex, and is based on morphology (growth form), mode of reproduction (sexual or asexual) and the disease caused.
The easiest way to look at different fungi is to consider the type of infection they cause.
- SUPERFICIAL mycoses: affect the skin, hair, nails and mucous membranes
- CUTANEOUS mycoses: affect the deep skin
- SYSTEMIC mycoses: affect the body’s systems
Describe the structure of parasites.
- they are single cells
- they have single or multiple nuclei
- they have haploid DNA
- their morphology varies throughout the life cycle
- they may have flagella
- trophozoites, cysts and other morphotypes are parts of their complex life cycles
Describe helminths (a type of parasite).
Helminths are multicellular parasitic worms. They have a different morphology and sizes at different life cycle stages. They can either be microscopic or visible to the eye.
They are categorised into three groups:
- CESTODES are tapeworms
- TREMATODES are flatworms or flukes
- NEMATODES are roundworms
List some examples of viruses.
- Herpes Virus
- HIV
- Ebola Virus
- Flu Virus
List some examples of bacteria.
- Campylobacter jejuni - causes food poisoning
- Clostridium perfringens - Gas Gangrene
List some examples of fungi.
- Tinea pedis - athlete’s foot
- Cryptococcus neoformans
List some examples of parasites.
- Plasmodium falciparum - malaria
- Entamoeba histolytica
- Trichomonas vaginalis - common STI
How are microbes visualised?
Bacteria, fungi, protozoa and certain lifecycle stages of helminths can be visualised using light microscopy.
Viruses at too small to be seen using light microscopy but can be visualised with an electron microscope after special staining. This allows detailed morphologic examination of the viruses.
