introduction to microbiology
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Introduction to microbiology. PSP1. virus. virus. Smallest known infective agent Most forms of life a susceptible to viral infection- humans, animals, plants, bacteria Need a host to replicate Requires entry to the host Respiratory tract Alimentary tract ( oral –faecal route) Blood - PowerPoint PPT PresentationTRANSCRIPT
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Introduction to microbiology
PSP1
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virus
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• Smallest known infective agent• Most forms of life a susceptible to viral infection-
humans, animals, plants, bacteria• Need a host to replicate• Requires entry to the host
– Respiratory tract– Alimentary tract ( oral –faecal route)– Blood– Sexual intercourse– Skin abrasions
virus
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• Basically :• a core of nucleic acid ( contains genetic
material DNA/RNA) surrounded by a protein coat
• Outer protein envelope
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replication• Often protein envelope partially derived from
the host cell• Virus always replicate INSIDE a host cell• Fragile outside a host cell1. Cause cell lysis- viral DNA replicated2. Remain latent within the cell , divide with the
cells natural division , virus DNA is replicated during this division
1. THEN cause lysis
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• Different virus attack different cells depending on the RECEPTOR SITE
• Systemic- spreads widely and infects many tissues and organs e.g. measles
• Localised- invades only tissues adjacent to the site of entry e.g respiratory viral infections/ verrucae
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• Main defence of the body is to produce the protein interferon
• Interferon is released by infected cells and taken up by other cells
• Antibodies appear in the patient's serum- this leads to immunity or resistance
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• Hepatitis A, Hepatitis B, and Hepatitis C are diseases caused by three different viruses
• different modes of transmission and can affect the liver differently.– Hep A- ingesting faecal matter ( often associated with
developing countries/travel)– Hep B- blood/body fluid– Hep C- blood/body fluid
• There are vaccines to prevent Hepatitis A and B;
however, there is not one for Hepatitis C.
Hepatitis
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HIV• Human immunodeficiency virus• AIDS- final stage of HIV infection• 1 in 5 affected people do not know they
have the virus• Transmitted through:
– Unprotected sex– Mother-baby– Contaminated needles
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bacteria
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• Single cell organisms• Classified in different ways ( three
parameters): • Shape- morphology• Colour ( Gram staining)• Growth requirements-Need for oxygen
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• Bacteria are named with 2 words ( genus + species)
• Staphylococcus aureus shortened to S.aureus
naming
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• Sphere ( cocci)– Staphylococcus – spheres bunch together– Streptococci- spheres form a chain
• Rods ( bacilli)• Spiral (spirochaetes)
morphology
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• Gram positive and gram negative refers to how a bacteria reacts to a gram stain.
• Chrystal violet then iodine• If it takes the initial stain, it will be purple and
be considered gram positive.• If it doesn't take the initial stain, it will be pink
and gram negative.
Gram staining
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• The difference is the outer casing of the bacteria.
• A gram positive bacteria will have a thicker layer of peptidoglycan (a sugar-protein shell)
• A gram negative bacteria has an outer membrane covering a thin layer of peptidoglycan on the outside.
Positive and negative
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• Aerobes need oxygen and are found on wound surfaces– E.g. Pseudomona aeruginosa
• Anaerobes cannot survive where there is oxygen and are found deep in wounds – E.g. Clostridium welchii – causes gas gangrene
Growth requirements
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Cultured on an agar plate
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• Gram positive• Staphylococcus aureus is a bacterium that
commonly colonises human skin and mucosa (e.g. inside the nose) without causing any problems. Normal body flora
• Common wound infector- may lead to cellulitis
• Methicillin Resistant Staphylococcus aureus
Staphylococcus aureus
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Pseudemonas aeruginosa
Common wound pathogenGram negativePyocyanin – green pigment secreted by the bacteriaOne of the most worrisome characteristics of P. aeruginosa is its low susceptibility to antibiotics
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Streptococcus pyogenes ( group A strep)•Gram positive•Faculative anerobe ( can survive with or without oxygen)•Part of normal flora in many people’s throats•Can cause simple infections ( sore throat) to life threatening infections•Most frequent pathogen in humans
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• Strep throat• Purulent infections• cellulitis• impetigo• necrotising fasciitis
( flesh eating)• Can lead to toxic
shock
Streptococcus pyogenes
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• MAY be found as part of normal skin flora
• Normally infections in patients with other co-morbidities e.g diabetes
• Wound infector• Can spread and
cause extensive infections: e.g.
• Bacteriamia• Septic shock
group G Strep
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FUNGIf
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Fungal hyphae
Multicellular fungi are composed of filaments called ‘hyphae’
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• More complex organism than bacteria• Reproduce by spore formation ( released by
splitting hyphae) or sexual reproduction ( mix chromosomes)
• Cell wall+ cell membrane• Ergesterol essential element of the cell
membrane – provides stability and flexibility
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fungi on skin and nails
DERMATOPHYTES infect keratinous material NON-DERMATOPHYTES Yeasts or moulds
Fungi cannot manufacture their own food. Dermatophytes ingest keratin as their food source
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• 3 genera– Trichophyton– Epidermophyton– Microsporum
• all endemic to communal areas
dermatophytes affecting the skin and nails
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Pathology
First resultPotassium hydroxide wet mount – dissolves
Keratin leaving resistant Fungal hyphae- seen through microscope
Second resultFungal culture- agar plate
Therefore 2 weeks for results to be returned from the pathology laboratory
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Tricophyton rubrum