Bacteria

Bacteria

1. Gram positive cocci

   • Aerobic
     • Staphylococcus: in clusters, catalase positive
       • Staphylococcus aureus:
         • Pneumonia, Cellulitis, Septic arthritis, Infective endocarditis, Line associated infection
         • MSSA – Methicillin sensitive SA MRSA – Methicillin resistant SA
         • Toxins: Scalded skin syndrome, Toxic shock syndrome, food poisoning
         • coagulase positive
       • Staphylococcus epidermidis
         • Coagulase negative
         • Part of normal skin flora, opportunistic pathogen
       • Staphylococcus saprophyticus
         • Causes UTI in women
         • Coagulase negative
     • Streptococcus - in chains, catalase negative
       • Beta haemolytic streptococci - Lancefield grouping
         • 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
         • Group B – strep agalactiae
           • Colonises the vagina, major cause of neonatal infections
             • Cellulitis, meningitis, endocarditis, bacteraemia
           • Adults - cellulitis, pneumonia, bone infection, UTI
         • Group D – enterococcus (can be alpha, beta or non-haemolytic)
           • Can cause UTI, abdominal infections, biliary tract infections
       • Alpha haemolytic streptococci
         • Strep pneumoniae (diplococci, sensitive to penicillin))
           • Adults - pneumonia and bacterial meningitis
           • Children - otitis media
         • Strep viridans
           • Commensals of upper respiratory and GI tract, colonise the mouth, cause infective endocarditis
         • Strep milleri
           • Lancefield group F, common cause of abscesses in abdomen, brain, chest

2. Gram positive bacilli

   • Spore forming
     • Bacillus
       • Bacillus anthracis
         • Exotoxins: Oedema factor, protective antigen, lethal factor. Anthroax in IVDU
       • Bacilllus cereus
         • Produces heat resistant spores, fried rice syndrome
     • Clostridium
       • Clostridium botulinum
         • toxin binds to presynaptic nerve endings and blocks Ach release. Causes descending flaccid paralysis
       • Clostridium tetani
         • In environment. Spores have drumstick appearance. Toxin prevents release of inhibitory neurotransmitters leading to sustained tetanic contraction. Causes lockjaw syndrome
       • Clostridium difficile
         • antibiotic associated diarrhoea and pseudomembranous colitis
   • Non-spore forming
     • Listeria monocytogenes
       • Important pathogen in pregnant women, neonates, immunocompromised and elderly. Causes foetal infection and miscarriage
     • Corynebacterium diphtheriae
       • angular/palisade formation
       • Causes diphtheria - respiratory infection with pseudomembrane in throat and bull neck

3. Gram negative cocci

   • Neisseria
     • Neisseria meningitidis
       • Vaccines for A, B and C serotypes available B most important for children
       • Endotoxin causes vascular necrosis and haemorrhage
     • Neisseria gonorrhoea
       • causes urethritis in men and pelvic inflammatory disease in women Rarely can cause septic arthritis or bacteraemia
       • Ophthalmia neonatorum - form of conjunctivitis contracted by the baby during vaginal birth if the mother has gonorrhoea or chlamydia

4. Gram negative bacilli

   • Food borne pathogens
     • Shigella
       • gastroenteritis with blood and mucus in diarrhoea. very low infectious dose (10-100)
       • S dysenteriae
         • Shiga toxin
     • Salmonella
       • Diarrhoeal disease
       • Typhoid
         • S typhi and S paratyphi
   • Normal gut flora
     • Escherichia coli
       • Commensal of intestinal tract. Common cause of UTI infections Commonest cause of gram negative bacteraemia
       • Pathogenic E coli
         • Enterotoxigenic E coli
           • Cholera-like symptoms
         • Enteropathogenic E coli
           • infantile gastroenteritis
         • Verocytotoxin producing E coli (VTEC) - E coli 0157
           • Haemolytic-uraemic syndrome and thrombotic thrombocytopaenic purpura
     • Enterobacter
     • Klebsiella
     • Proteus
     • Serratia
     • Pseudomonas aeurginosa
       • leg ulcers
       • Infection in burns
       • Bronchiectasis
         • Big problem in CF
       • Very resistant

5. Small gram negative bacilli/cocco-bacilli

   • Haemophilus influenzae
     • Epiglottitis, meningitis, lower respiratory tract infections, otitis media
   • Legionella pneumophila
     • Lives in water systems, causes atypical pneumonia

6. Curved gram negative bacilli

   • Campylobacter - foodborne pathogen, cramping abdo pain, bloody diarrhoea
   • Helicobacter - peptic ulcer disease
   • Vibrio cholera - rice water stools

7. Spirochaetes

   • Treponema pallidum
     • Syphilis
   • Borrelia burgdorferi
     • Lyme disease