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MICRO

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mestrella's version from 2016-12-02 15:50

Section 1

Question Answer
SBA small zone of hemolysis =Listeria monocytogenes
HEK =Hektoen enteric agar
HEK indicateslactose fermentation and hydrogen sulfide production (also prevent the growth of Gram-positive bacteria)
HEK recovers sppSalmonella and Shigella
HEK mechanismPeptone (carbon source) metabolism turns pH indicator blue
HEK green colonies =No H2S production = Shigella
HEK ddx componentthiosulfate or ferric ammonium citrate (Turns black w/ H2S)
HEK moa for inh Sulfer reducing sppbile salts
MAC select/diff sppGram-negative and enteric (normally found in the intestinal tract) bacilli and differentiate them based on lactose fermentation
MAC moacrystal violet and bile salts inhibit the growth of gram-positive organism
MAC - NaCl sppProteus
MAC + crystal violetcheck if G(+) are inhibited
MAC + sorbitolE. coli
MAC pink colonies =Lac+/ Escherichia coli, Enterobacter and Klebsiella will produce acid
MAC white/colorless colonies =Salmonella, Proteus species, Yersinia, Pseudomonas aeruginosa and Shigella
MAC agar typeindicator, low selective
MAC slow Lac+Serratia and Citrobacter.
MAC mucoid colonies Klebsiella and Enterobacter, produce mucoid colonies which appear very moist and sticky. This phenomenon happens because the organism is producing a capsule, which is predominantly made from the lactose sugar in the agar.
A variant, Sorbitol-MacConkey agar,E. coli O157:H7, by the presence of colourless circular colonies that are non-sorbitol fermenting.
Nutritive Agar purpose (NA)non-fastidious organisms
NA 0.5% Peptone =organic nitrogen
NA 0.3% beef extract/yeast extract =vitamins, carbohydrates, nitrogen, and salts
NA 0.5% Sodium Chloridecytoplasmic environment
Oxidase tests for production of cytochrom c oxidases
Oxidase test: disks impregnated withTMPD or DMPD, artificicial electron donors, redox indicators
OX+ colordark-blue to maroon
OX - colorcolorless
Campylobacter OX (?)+, like low o2 environments
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Section 2

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