Infectious agents Flashcards
What are the classifications of microbes
-Viruses
-Bacteria
-Fungi
-Parasites(Protozoa, helminths and ectoparasites)
What is the size range for viruses?
-Most are 20nm to 300nm
What is the structure of viruses?
DNA or RNA(not both) core within protein capsid bade up of individual capsomeres with a helical, cubic or more complex arrangement
Do viruses have cytoplasm?
No Cytoplasm
What may the envelopes from viruses be derived from?
-May have envelope derived from host cell
What components are membrane bound in viruses?
Proteins are membrane bound
What is a rotavirus?
A cause of infantile diarrhoea
What can adenoviruses cause?
-May cause diarrhoea, respiratory tract infections, keratitis, hepatitis
What arrangement can adenoviruses have?
-May have an icosahedral arrangement
What is the size range of bacteria?
-0.5μm to 3μm
What is the structure of bacteria
-Prokaryotic
-Haploid DNA
-No nucleus
-Usually have a rigid cell wall outside cytoplasmic membrane
-No mitochondria
-some may have flagella
Structure of Gram positive bacteria cell wall
-Gram positive bacteria have a thick layer of peptidoglycan and no outer lipid membrane
Structure of Gram negative bacteria
-Gram negative bacteria have a thin peptidoglycan later and have an outer lipid membrane
What bacteria causes urinary tract infection?
Proteus mirabilis is the cause of a urinary tract infection
What does bacterial growth require?
-Carbon
-Water
-Nitrogen
-Nutrients
-Minerals
-Correct pH, osmotic pressure, temperature, atmosphere
By what process does bacterial growth occur?
-Growth occurs by binary fusion
What is the approx doubling time for bateria?
-Doubling time approx 20-30 mins
How many hours does it take for mycobacterium tuberculosis to double?
-Mycobacterium tuberculosis approx takes 18 hours to double
What oxygen environment do strict aerobes grow in?
Free oxygen
What oxygen environment do facultative aerobes grow in?
Free oxygen and absence of oxygen
What oxygen environment do strict anaerobes grow in?
Absence of oxygen
What oxygen environment do microaerophil anaerobes grow in?
Absence of oxygen
What is the size of fungi?
Size is over 2μm
What is the structure of fungi?
-Eukaryotic
-Haploid or diploid DNA
-Single or multiple nuclei
-Rigid chitinous cell wall outside cytoplasm.
-May be multicellular
-May be dimorphic
What are parasites?
Single or multicellular eukaryotic organisms
What type of cell is protozoa?
Single cell
Size range of protozoa
5 to 300μm
What is the nuclei like in protozoa
Single or multiple nuclei
What are the 3 main groups of eukaryotic parasites?
-Cestodes
-Trematodes
-nematodes
What is an example of cestodes and how do they get into humans?
-an example would be beef tapeworm
1. Egg shed in faeces
i) Ingested by cows
2. This develops into cysts in beef which is eaten by humans
3. This then develops into adult tapeworm from GI tract
What is an example of trematode and how does it get into humans?
-an example would be flukes flatworms
1. Egg shed in urine by human
i) Hatches into miracidium that infects a freshwater snail, where it develops further.
2. It is then release as cercaria in water
ii) It penetrates skin of human and enters circulation to migrate to venules of bladder or bowel before maturing into an adult fluke in humans
What is an example of nematodes and how do they get into humans?
-an example is roundworms
1. Egg shed in faeces
i) If ingested by humans, it will develop into larvae and enter circulation to migrate to lungs. Coughed up and then swallowed to re-enter the gut.
2. This then develops into an adult worm
What are ectoparasites and what are examples of it?
-Parasites that live on the skin
-Example
-Human body louse
-Human flea
-Ticks
-Mites
How can bacteria, fungi, protozoa and helminths be seen?
-Bacteria, fungi, protozoa and helminths can be seen using light microscopy x400-x1000
What can viruses be seen by?
-Viruses can be seen by electron microscopy x40,000
What does gram staining do?
-Separates between gram positive and gram negative bacteria
What colour is gram positive bacteria stained as?
-Gram positive bacteria is blue/purple
What colour is gram negative bacteria stained as?
-Gram negative bacteria is red
What are the 2 main morphologies of bacteria?
-Cocci
-Rods or bacilli
How do cocci appear under microscope?
Spherical
