Bacteria

Bacteria

Gram positive cocci
1. Aerobic
  1. Staphylococcus: in clusters, catalase positive
    1. Staphylococcus aureus:
      1. Pneumonia, Cellulitis, Septic arthritis, Infective endocarditis, Line associated infection
      2. MSSA – Methicillin sensitive SA MRSA – Methicillin resistant SA
      3. Toxins: Scalded skin syndrome, Toxic shock syndrome, food poisoning
      4. coagulase positive
    2. Staphylococcus epidermidis
      1. Coagulase negative
      2. Part of normal skin flora, opportunistic pathogen
    3. Staphylococcus saprophyticus
      1. Causes UTI in women
      2. Coagulase negative
  2. Streptococcus - in chains, catalase negative
    1. Beta haemolytic streptococci - Lancefield grouping
      1. Group A - strep pyogenes Very sensitive to penicillin!
        Non-invasive infection - scarlet fever, pharyngitis (strep throat), erysipelas (infection of the skin affecting the upper layers)
        Invasive infections - streptococcal toxic shock syndrome, necrotising fasciitis, bacteraemia
        Delayed antibody mediated immune response - response to past strep infection
        Rheumatic fever
        Acute post strep glomerulonephritis
      2. Group B – strep agalactiae
        Colonises the vagina, major cause of neonatal infections
        Cellulitis, meningitis, endocarditis, bacteraemia
        Adults - cellulitis, pneumonia, bone infection, UTI
      3. Group D – enterococcus (can be alpha, beta or non-haemolytic)
        Can cause UTI, abdominal infections, biliary tract infections
    2. Alpha haemolytic streptococci
      1. Strep pneumoniae (diplococci, sensitive to penicillin))
        Adults - pneumonia and bacterial meningitis
        Children - otitis media
      2. Strep viridans
        Commensals of upper respiratory and GI tract, colonise the mouth, cause infective endocarditis
      3. Strep milleri
        Lancefield group F, common cause of abscesses in abdomen, brain, chest
Gram positive bacilli
1. Spore forming
  1. Bacillus
    1. Bacillus anthracis
      1. Exotoxins: Oedema factor, protective antigen, lethal factor. Anthroax in IVDU
    2. Bacilllus cereus
      1. Produces heat resistant spores, fried rice syndrome
  2. Clostridium
    1. Clostridium botulinum
      1. toxin binds to presynaptic nerve endings and blocks Ach release. Causes descending flaccid paralysis
    2. Clostridium tetani
      1. In environment. Spores have drumstick appearance. Toxin prevents release of inhibitory neurotransmitters leading to sustained tetanic contraction. Causes lockjaw syndrome
    3. Clostridium difficile
      1. antibiotic associated diarrhoea and pseudomembranous colitis
2. Non-spore forming
  1. Listeria monocytogenes
    1. Important pathogen in pregnant women, neonates, immunocompromised and elderly. Causes foetal infection and miscarriage
  2. Corynebacterium diphtheriae
    1. angular/palisade formation
    2. Causes diphtheria - respiratory infection with pseudomembrane in throat and bull neck
Gram negative cocci
1. Neisseria
  1. Neisseria meningitidis
    1. Vaccines for A, B and C serotypes available B most important for children
    2. Endotoxin causes vascular necrosis and haemorrhage
  2. Neisseria gonorrhoea
    1. causes urethritis in men and pelvic inflammatory disease in women Rarely can cause septic arthritis or bacteraemia
    2. Ophthalmia neonatorum - form of conjunctivitis contracted by the baby during vaginal birth if the mother has gonorrhoea or chlamydia
Gram negative bacilli
1. Food borne pathogens
  1. Shigella
    1. gastroenteritis with blood and mucus in diarrhoea. very low infectious dose (10-100)
    2. S dysenteriae
      1. Shiga toxin
  2. Salmonella
    1. Diarrhoeal disease
    2. Typhoid
      1. S typhi and S paratyphi
2. Normal gut flora
  1. Escherichia coli
    1. Commensal of intestinal tract. Common cause of UTI infections Commonest cause of gram negative bacteraemia
    2. Pathogenic E coli
      1. Enterotoxigenic E coli
        Cholera-like symptoms
      2. Enteropathogenic E coli
        infantile gastroenteritis
      3. Verocytotoxin producing E coli (VTEC) - E coli 0157
        Haemolytic-uraemic syndrome and thrombotic thrombocytopaenic purpura
  2. Enterobacter
  3. Klebsiella
  4. Proteus
  5. Serratia
  6. Pseudomonas aeurginosa
    1. leg ulcers
    2. Infection in burns
    3. Bronchiectasis
      1. Big problem in CF
    4. Very resistant
Small gram negative bacilli/cocco-bacilli
1. Haemophilus influenzae
  1. Epiglottitis, meningitis, lower respiratory tract infections, otitis media
2. Legionella pneumophila
  1. Lives in water systems, causes atypical pneumonia
Curved gram negative bacilli
1. Campylobacter - foodborne pathogen, cramping abdo pain, bloody diarrhoea
2. Helicobacter - peptic ulcer disease
3. Vibrio cholera - rice water stools
Spirochaetes
1. Treponema pallidum
  1. Syphilis
2. Borrelia burgdorferi
  1. Lyme disease

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	Created by Merike Mikkov over 7 years ago