Introduction to microbiology PSP 1 virus virus Smallest

Introduction to microbiology PSP 1

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 Sexual intercourse Skin abrasions

• Basically : • a core of nucleic acid ( contains genetic material DNA/RNA) surrounded by a protein coat • Outer protein envelope

replication Often protein envelope partially derived from the host cell • Virus always replicate INSIDE a host cell • Fragile outside a host cell 1. Cause cell lysis- viral DNA replicated 2. Remain latent within the cell , divide with the cells natural division , virus DNA is replicated during this division • 1. THEN cause lysis

• 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

• 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

Hepatitis • 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.

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

bacteria

• • • Single cell organisms Classified in different ways ( three parameters): Shape- morphology Colour ( Gram staining) Growth requirements-Need for oxygen

naming • Bacteria are named with 2 words ( genus + species) • Staphylococcus aureus shortened to S. aureus

morphology • Sphere ( cocci) – Staphylococcus – spheres bunch together – Streptococci- spheres form a chain • Rods ( bacilli) • Spiral (spirochaetes)

Gram staining • 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.

Positive and negative • 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.

Growth requirements • 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 gangrene

Cultured on an agar plate

Staphylococcus aureus • 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

Pseudemonas aeruginosa Common wound pathogen Gram negative Pyocyanin – green pigment secreted by the bacteria One of the most worrisome characteristics of P. aeruginosa is its low susceptibility to antibiotics

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

Streptococcus pyogenes • • • Strep throat Purulent infections cellulitis impetigo necrotising fasciitis ( flesh eating) • Can lead to toxic shock

group G Strep • MAY be found as part of normal skin flora • Normally infections in patients with other comorbidities e. g diabetes • Wound infector • Can spread and cause extensive infections: e. g. • Bacteriamia • Septic shock

f FUNGI

Fungal hyphae Multicellular fungi are composed of filaments called ‘hyphae’

• 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

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

dermatophytes affecting the skin and nails • 3 genera – Trichophyton – Epidermophyton – Microsporum • all endemic to communal areas

Pathology First result Potassium hydroxide wet mount – dissolves Keratin leaving resistant Fungal hyphae- seen through microscope Second result Fungal culture- agar plate Therefore 2 weeks for results to be returned from the pathology laboratory

Tricophyton rubrum