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MCB (Subject) / Oversight Pathogens (Lesson)

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• Differences Eukaryotes - Prokaryotes 1. DNA  a) P: singel circular chromosome without nucleus + plasmids  b) E: Nucleus with genome + mtDNA 2. Energy production a) P: membrane co-ordinates electron transport and oxidative phosphorylation  --> invaginated membrane for an enlarged surface  b) E: Mitochondria  3. Robosomes  a) P: 70s  b) E: 80s 4. Organelles a) P: Ribosomes b) E: Golgi apparatus/bodies, Mitochondria, ER, Lysosomes, Peroxisomes
• What is Gram staining? - a staining method to differentiate bacteria into two distinct groups  - Gram postive bacteria stain purple, negative stain red/pink
• Gram staining procedure 1. Gentian violet - stains both types violett 2. Lugol - iodine solution forms a crystal violet iodine complex  3. Washing with ethanol - extracts the violett dye from the gram-negative bacteria --> colorless 4. Counter stain fuchsin - stains decolorised gram-negative cells red/pink
• Surface structure gram-positive bacteria + expl. staining - Cytoplasmic membrane  - Thick cell wall: severeal peptidoglycan layers with ramifications (polysaccharide chains + amino acid side chains) - teichoic acids + lipoteichoic acids --> antigens  --> violett stain resudes in the peptidoglycan layers/network and doesn't get washed out by the ethanol 
• Surface structure Gram-negative bacteria + expl. stain - Cytoplasmic membrane  - thin cell wall (1-2 layers peptidoglycan without ramifications)  - Outer membrane made of lipopolysaccharides (LPSs) --> Ethanol destroyd the outer membrane and washed the violett stain out of the peptidoglycan
• Exeptions from gram stain - bacteria with mycolitic acids in their cell walls don't gram stein --> acid-fastness --> e.g. mycobacterium (TB), chamydia, mycoplasma
• External structures and functions of bacteria 1. Pili - hair-like protein structures --> adhesion to mucosal surfaces and transfer of genetic information (sex pili) 2. Flagellae - long filamentous structures --> locomotion  3. Capsules - outermost layer of jelly-like hydrophilic jelly --> protection from phagocytosis  4. Spores - under adverse conditions formed, have no metabolism and are extremey resistant (e.g. clostridium difficile and tetani)
• Endotoxins (structure + effects) 1. Structure - consist of Lipopolysaccharids (LPS) which are part of gram neg. bacteria outer membrane  --> part of physiological activity (e.g. bacterial outer membrane vesicles) and not made to be toxic  2. Effect  - Relese of cytokines from various cells - Activation of complement system - Damage to capillary blood vessels --> fluid leaking into tissues, leading to drop in blood pressure  - Non-specific blood coagulation --> thrombus formation --> e.g. Neisseria Meningitis (meningococcus)
• Exotoxins (Def.+ Structure) 2. Definition - proteins secreted by many gram pos. and some gram neg. bacteria which are highly specific --> direct effect on virulence and potential target for neutralising antibodies  2. Structure  - Subunit A - enzymatic activity (toxic) - Subunit B - binding to specific host cell receptor (non-toxic)
• Exotoxin I - Cholera (Pathogenesis + effect) 1. Pathogenesis - large dose required to survive stomach acid and reach the small intestine --> V. cholerae have flagellae to swim through the gut mucous  - recognise specific sugars on epithelial cell surface, adhere to it and secrete cholera toxin 2. Effect  - Secretion of cholera toxin --> binding to ganglioside receptor on epithelial cells --> A-subunits enter cells --> cleavage into A1 + A2 --> increased adenylate cyclase activity --> increased cAMP --> efflux of ions and water (loss of nutrients) --> diarrhea
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• Exotoxin II - Clostridia tetani (what + mechanism) - C. botulinum and C. tetani release neurotoxins --> most potent known toxins 1. C. tetani - spore forming, found in soil and animal faeces, low O2 leads to spore germination followed by toxin production and release --> leads to muscle spasms, paralysis of respiratory muscles  a) Mechanism - C. tetani releases tetanospasmin --> inhibits release of inhibitory neurotransmitter in the post-synaptic cell --> Continuous stimulation by excitatory transmitter 
• Immunisation (Toxoids, types of vaccine) 1. Toxoids detoxified toxins retain immunogenicity -> e.g. tetanus toxoid (toxin treated with formaldehyde) 2. Types of vaccine a) Polysaccharide only - against bacterial capsules (consist of polysaccharides) --> hydrophilic jelly which prevent phagocytosis - Problem: ability to respond to polysaccharides develops later in life than protein response --> poorly immunogenic in children - Polysaccharided don't induce T-helper cell activity --> shirt lived IGM antibodies, no T-memory cells --> only short termed immunity b) Polysaccharide-conjugate  - Polysaccharide coupled to a carrier protein --> elicits a protein-like response - T-cell dependant response --> long lived IgG antibodies, immunological memory, immunogenic in infants 

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