microfinal review - Microbiology Spontaneous generation...

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Growth Problems: n=number of doublings (generation) g=generation time t=time N t =number of bacteria at t time N o =initial number of bacteriak=doublings/time g=t/n N t =N o x 2 n logN t – logN o /0.301 = n g= 0.301t/logN t - logN o k=1/g Koch’s Postulates: 1. The suspected pathogenic organism should be present in all cases of the disease and absent from healthy animals 2. The suspected organism should be grown in pure culture away from the animal’s body 3. Such a culture when inoculated into susceptible animals, should initiate the characteristic disease symptoms 4. The organism should be reisolated and shown to be the same as the original Gram + vs. Gram – Cell walls 1. Gram +: Peptidoglycan- A rigid layer or sheet composed of two sugar derivatives, N-acetylglucomamine and N-acetylmuramic acid and a small group of amino acids consisting of L-alanine, D-alanine, D-glutamic acid and either lysine or diaminopimelic acid (DAP). 2. Gram -: Besides peptidoglycan, gram(-) Bacteria contain an additional wall layer, LPS, made of lipopolysaccharide and called the outer membrane . This second lipid bilayer contains polysaccharides and lipids which are linked in the outer membrane to form lipopolysaccharide structures This outer layer is called the lipopolysaccharide layer (LPS) Dilution: 0.2ml transftered into a 4.8 mL blank 0.2ml/(4.8ml+0.2)mL= 0.2mL/5.0mL = 0.04mL dilution Viable plate count # of bacteria in countable plate/#mL transferred from flask= #bacteria/mL in flask #bacteria/mL in flask x (1/dilution factor) = #bacteria /mL of original
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microfinal review - Microbiology Spontaneous generation...

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