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Gastrointestinal Infections: Toxins

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Medical Microbiology Mind Map on Gastrointestinal Infections: Toxins, created by hands97 on 30/04/2013.
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Mind Map by hands97, updated more than 1 year ago
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Resource summary

Gastrointestinal Infections: Toxins
  1. C. Botulinum
    1. Neurotoxin: Inhibits acetylcholine release from nerve endings, flaccid paralysis
      1. Heavy (100kDa) & Light Chain (50kDa, metalloprotease, HexxH zinc-binding motif, cleaves SNARE complex, ie SNAP-25, synaptobrevin, or syntaxin)
      2. Types A-G but food-bourne usually A,B,D, E (marine)
        1. Therapy= antitoxins to mop up free toxin
          1. Difficult to diagnose: Similar to stroke symptoms. Need to isolate toxin from faeces/CSF/serum, takes 2+ days to show!
            1. Mouse bioassay (4 days), new PCR developed
            2. G+ve, spore forming (survive high temps), anaerobe
              1. Outbreaks through contaminated food- preserving/canning process inadequate
                1. Incubation: 6hrs-16days
                  1. Vaccine for high risk workers,e.g. scientists
                    1. Infant botulism: Linden flowers implicated, natural sedative
                    2. S. aureus
                      1. G+, coccus, facultative anaerobe
                        1. Stable over range of pH/salt/temps
                          1. Staph enterotoxin, heat-resistant
                            1. Abdominal pain, vomiting, fever
                              1. Catalase +ve, coagulase/DNAse +ve
                                1. 20-100ng enough to cause infection
                                  1. Protein-rich foods, e.g. dairy/meat
                                    1. Incubation: 1-6hrs, infection:<48hrs
                                      1. Enter text here
                                      2. B. cereus
                                        1. Cereulide (emetic toxin), cyclic dodecadepsipeptide
                                          1. Highly resistant to acid/proteolysis, heat
                                            1. Bind 5HT3 receptor on vagus afferents (nerve fibres) to stimulate sickness
                                              1. Inhibits fatty acid oxidation in mitochondria, possible liver toxicity
                                                1. Encoded on a megaplasmid, via ces genes
                                                  1. PlcR regulated expression
                                                  2. 103-108 infectious dose (high)
                                                    1. Can cause meningitis, UTIs, RTIs, HAIs!
                                                      1. RTIs: carries anthracis pX01 plasmid (but no pX02- required for capsule+positive regulator of toxin genes on pX01)
                                                        1. HAIs: amongst immunosuppressed patients, equipment contaminated e.g. ventilators, intravenous catheters, etc
                                                          1. Meningitis, meningoencephalitis, brain abscess, etc. Abdominal pain before bacteremia-->brain. Risk factors include intrathecal induction chemotherapy
                                                            1. UTIs: Contaminant on catheter (forms biofilm)--->pyelonephritis.
                                                            2. Diarhoeal toxins
                                                              1. Tripartite (Cytotoxin K & Nonhaemolytic Enterotoxin)

                                                                Annotations:

                                                                • NHe most dominant!!
                                                                1. L1, L2 (lytic) & B (binding) subunits (CytK), NHeA, NHeB, NHeC (NHe)
                                                                  1. NHe= pore former
                                                                  2. Oligomeric B-barrel pore-forming (Haemoysin bl & CytK)
                                                                    1. Cerelysin O
                                                                      1. Haemolysin II
                                                                        1. HlyIIR, dimeric transcriptional regulator (repressor)
                                                                        2. InhA2
                                                                          1. phospholipase C
                                                                          2. G+ve, facultative-to-aerobic, spore-forming (resistant to gamma radiation/pasteurisation), non-mannitol fermentor
                                                                            1. Some strains produce negligible amounts of toxin & authorised for use as probiotic!
                                                                              1. Vomiting infection: 8-10hours, diarrhoeal infection: 20-36hrs
                                                                              2. C.perfringens
                                                                                1. G+ve, spore-forming, anaerobic
                                                                                  1. IN NORMAL FAECAL FLORA
                                                                                    1. Incubation: 8-14hrs, infection: 24hrs
                                                                                      1. Peaks in autumn (stews)
                                                                                        1. Toxins
                                                                                          1. CPE (enterotoxin)
                                                                                            1. Bind claudin -3, -4, -8, -14
                                                                                              1. Oligomerises into hexamer (CH1)
                                                                                                1. Influx of Ca2+ into cell--> apoptotic pathway
                                                                                                2. CH2
                                                                                                  1. Internalises occludin
                                                                                                    1. Histopathologic damage to cells--> diarrhoea
                                                                                                  2. Cytoplasmic C and N termini, 4 transmembrane domains
                                                                                                  3. Iota toxin
                                                                                                    1. ADP-ribosyltransferase
                                                                                                      1. CD44 binding implicated
                                                                                                    2. Non-motile
                                                                                                    3. V. cholerae
                                                                                                      1. C. Difficile
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