Immunity and infection Flashcards
Classify microbes into 4 broad biological groups
microbes can be classified into: bacteria, viruses, fungi, parasites (Protozoa and helminths)
Describe and explain viruses
Viruses are 20-300nm, obligate intracellular organisms. Can have DNA or RNA (not both) core w/in protein capsid made up of capsomeres
Can have a helical, cubic or more complex arrangement
No cytoplasm
May have envelope derived from host cell
Has membrane bound proteins
Viruses replicate by a variety of mechanisms
Draw and label a simplified virus structure
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Describe some common viral infections in the UK and their origin
Upper resp tract infection: influenza, RSV, covid
Gastroenteritis: Norovirus and adenovirus
Rashes: varicella zoster virus (chickenpox), measles
Meningitis e.g. enterovirus
Hospital Acquired infection: Norovirus
Draw and label the basic structure of a bacterium
Describe gram positive bacterial cell walls, and how penicillin targets them
Gram-positive consists of a thick peptidog layer and teichoic acid.
Peptidoglycan cross linkages is the target site for penicillins.
Crystal violet in the stain binds to teichoic acid and resists decolouring to leave a purple colour
Describe gram negative bacterial walls
Gram-neg wall consists of an outer membrane. This is made of phospholipids, lipopolysaccs, proteins and protein channels called porins.
Between the outer membrane and cell membrane hay the periplasmic space. This stores antibiotic inactivating enzymes in some bacteria. Hay a thin peptidog layer in this space.
What other features do bacteria have?
Flagella/axial filaments for independent movement.
Some bacterial surfaces have pili or fimbriae, involved in conjugation and help attachment to different mucosal surfaces.
Outside the cell wall, a capsule and slime layer adhere to other membranes and prevent phagocytosis.They are also antigenic.
Describe how bacteria grow in certain conditions
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List some common bacterial infections and where they originate from
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Describe and explain fungi
Fungi are over 2μm, eukaryotic, w single or multiple nuclei. Has haploid or diploid DNA and a rigid chitin cell wall.
May be uni or multicellular
May be dimorphic (switch between yeast and mould).
Classified based on morphology and mode of reproduction: sexual, teleomorphasexual, anamorph
How else can fungi be classified?
It’s easier to classify fungi by the type of infection they cause:
Superficial mycoses of skin, nails, hair and mucous membranes e.g. ringworm or thrush
Subcutaneous mycoses e.g. mycetoma
Systemic mycoses e.g. Histoplasmosis.
Describe protozoa
Protozoa: Single cell. 5-300 μm. Single or multiple nuclei. Haploid DNA. Morphology varies throughout life cycle. May have flagella.
Eg Plasmodium sp. which causes malaria
Describe helminths, a type of parasite
Helminths: multicellular parasitic worms. Can be microscopic or visible to the naked eye.
Helminths can be divided into:
Cestodes: tapeworms
Trematodes: flatworms or flukes.
Nematodes: roundworms
How else are bacteria visualised apart from microscopy?
Suspended in liquid broth- when live, some bacteria are seen being motile, others seen spinning at the same spot (Brownian movement.)
Bacteria is seen more easily if stained by Gram
How can we classify bacteria by shape and arrangement?
Spherical bacteria= cocci, bacilli= rod shaped.
Spirochaetes= helical, Vibrios= comma shaped.
Lanceolate=shaped like a lancet (arched window).
Arranged in pairs, eg diplococci, in chains eg streptococci, or in clusters e.g staphylococci.
Describe explain a bacterial growth curve
Bacteria must adjust to the new environment before multiplying (lag).
Bacterial growth reaches full potential w exponential growth (log).
Depletion of nutrients slows growth and causes some death- (stationary)
When nutrient is fully exhausted, bacterial growth fully ceases (death phase)
What is microbiota?
The human microbiota consists of the 10-100 trillion symbiotic microbial cells harboured by each person.