Bms1026 Bacteria

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Bacterial components

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- Nucleiod: contains circular DNA
- Ribosomes: site of protein synthesis, made of RNA and protein (smaller than eukaryote)
- Cytoplasm: a thick, semi transparent and elastic substance about 80% water
- Cell membrane: phospholipid bilayer which contains carrier proteins to act as semi-selective barrie
- Flagellum: for movement made of 3 components (long spiral filament attached to a hook to transmit torque and a motor to drive rotation )
- Capsule/Slime layer: extra polymeric material, acts as survival technique to evade immune system and prevent dehydration (capsule = firmly attach + highly organised, Slime layer = unorganised + loosely attached)
- Pili/Fimbriae: hair like appendages, shorter and stronger than flagellum, form biofilms and attachment of cells and to transfer DNA between cells (conjugation)
- Cell wall: rigid to prevent rupturing by peptidoglycan, acts as an antigenic.

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Gram +ve Vs Gram -ve

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- Gram +ve: one cell membrane, thick cell wall with more peptidoglycan and teicholic acid
- Gram -ve: two cell membranes, thin cell wall with less peptidoglycan so less rigid with lipopolysaccharides
- differentiated by gram stain

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Identification - Symptoms of disease

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- different bacteria cause different symptoms which make then distinct eg specific rashes.
- can be misinterpreted but also speedy identification if fast showing symptoms

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Identification - Microscopy

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- Shape of cell (cocci, coccobacillus, rod, diplococci, diplobacillus) and growth pattern (bunch of grapes, chain, palisade) are distinctive to different species of bacteria
- Can use light field, dark field, fluorescence, staining microscopy.
- can be misinterpreted but is speedy

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Identification - Cultivation

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- use agar to observe growth (colour, shape, size, smell and effect on media)
- broth to allow growth of sample
- sloppy agar to see mobility
- more accurate, slow

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Identification - Biochemistry tests

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- analysis of sugar fermentation products
- analysis of enzymes
- growth under aerobic/anaerobic conditions
(API, catalase and O/F test)
- more accurate, slow

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Identification - Immunological tests

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- interaction of a microbial antigen with an antibody
- can also look at antibodies produced by host
- rapid, only as good as test (need to confirm with other tests)

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Identification - Genetic methods

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- PCR, amplify sample and use DNA fingerprinting to determine genetic code and thus identify bacteria
- cant tell if bacteria is alive or dead, but does tell the exact type of bacteria

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Bacterial growth - Binary fission

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- increases in number of cells not size, cell splits into 2 identical daughter cells which then split into 4 etc
- exponetial growth N=N0 x 2^n where N0 is number at time 0, n is number of generations
-dependent on space, nutrients, predadation, competition etc

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Bacterial growth - Pattern on growth

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- Lag phase: slow growth, time for chemical composition and cell functions
- Exponential/Log phase: exp. growth (max doubling time, when nutrients in excess)
- Stationary phase: no. remains stable (cell death = cell growth
- Death phase: no. decrease (cell death > cell growth)

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Bacterial growth - Measurement

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- Directly: microscopy, flow cytometer, plate counts
- Indirectly: optical density (OD), dry weight of sample, measuring respiration activity.
- OD = very rapid, simple, cheap once have equipment, inaccurate as measures live and dead cells, cant use on pigment samples or on certain sizes
- Microscopy = cant differentiate dead/alive without staining, conc sample needed, no record for later studies, easy, suitable for non-culturable species, rapid results
- Plate count = detect viable bacteria for viable count, detects lower numbers, can be saved and restudied, time consuming, requires prior knowledge of growth requirements, slower (have to what for growth)