Infectious Agents
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What are the 4 biological groups of microbes?
• viruses • bacteria • fungi • parasites (protozoa, helminths)
What are key features of viruses?
• 20nm to 300nm • DNA OR RNA core in protein capsid + capsomeres • helical, cubic or more complex • no cytoplasm • envelope (derived from host cell)
What are common viral infections in the UK?
Community: • upper resp tract infection - rhinovirus, influenza, RSV • gastroenteritis eg. Norovirus, rotavirus, adenovirus HC-associated infection: - norovirus
What are key features of bacteria?
• 0.5 μm to 3 μm • prokaryotic • haploid DNA • no nucleus or mitochondria • rigid cell wall (peptidoglycan)
What are some important differences between prokaryotic and eukaryotic cells?
Prokaryotes vs eukaryotes • 1 vs many chromosome • no nuclear membrane vs nuclear membrane • no mitochondria vs mitochondria • no sterols vs sterols • 70s vs 80s ribosomes • no introns vs introns
What are differences between bacterial gram-positive and gram-negative cell walls?
Gram positive = thick peptidoglycan layer • no outer membrane • stain blue/purple Gram negative = thin peptidoglycan layer • no teichoic acids traversing wall • lots of lipids + lipoproteins • stain red
How do bacteria grow?
By binary fission, doubling time takes 20-30 mins
What conditions does bacterial growth require?
• carbon, water, nitrogen • nutrients + minerals • correct pH, osmotic pressure, temp (35-37C), atmosphere
What are common bacterial infections in the UK?
Community: • UTI - E.coli • Pharyngitis - streptococcus pyogenes HC-associated infection: • Post op - staphylococcus aureus -> MRSA • vent-associated pneumonia (on ITU) - pseudomonas aeruginosa
Describe key features of fungi
• over 2μm • eukaryotic • haploid or diploid DNA • single or multiple nuclei • rigid chitinous cell wall • multicellular or dimorphic sometimes
What is the difference between a teleomorph and anamorph?
teleomorph - sexual anamorph - asexual
What is mycoses and examples?
Mycosis is a fungal infection in animals • superficial mycoses (mucous membranes eg. ringworm or thrush) • subcutaneous mycoses (mycetoma) • systemic mycoses (histoplasmosis)
What are some key features of parasites?
eukaryotic • protozoa: eg. plasmodium sp - malaria • -> single cell, 5-300μm, haploid • helminths: eg. cestode/tapeworm, trematoda, nermatodes • -> parasitic worms, multicellular, visible to naked eye
Which microbe group cannot be visualised by light microscopy?
Viruses - require EM x40,000
What are the two main morphologies of bacteria?
Cocci - spherical bacilli/rods - cylindrical