BackMicrobiology Practical Study Guide Flashcards
03:16
Terms in this set (27)
A medium containing inhibitors that stop the growth of some organisms, allowing only certain bacteria to grow.
A medium with a substrate and indicator that causes different organisms to produce distinct visible changes, like color differences.
A medium where every ingredient and amount is known, allowing precise control of growth conditions.
Detects if an organism ferments a specific carbohydrate and produces acid and/or gas.
Yellow color indicates acid production; a bubble in Durham tube indicates gas production.
Mixed acid fermentation producing stable acids that lower pH to ≤4.4, detected by methyl red turning red immediately.
2,3-butanediol fermentation producing acetoin, which oxidizes to diacetyl and reacts to form a red color within 60 minutes.
Indole +, Methyl red +, Voges-Proskauer −, Citrate − (pattern ++−−).
Growth on Simmons citrate agar with blue color change or growth without color change indicates citrate use.
Pink color in urea broth within 24 hours indicates rapid urease activity producing ammonia and raising pH.
Green color after adding ferric chloride indicates phenylpyruvic acid production from phenylalanine deamination.
Catalase enzyme breaks down hydrogen peroxide into water and oxygen, producing visible bubbles.
Dark blue or purple color within 20 seconds indicates presence of cytochrome c oxidase enzyme.
Gas in Durham tube or red color after reagents A and B, or no color after zinc addition, indicates nitrate reduction.
Clear halo around growth after adding iodine indicates starch breakdown by amylase.
Clear zone around growth on skim milk agar indicates protease (caseinase) activity breaking down casein.
Dark blue precipitate or depleted oil droplets on spirit blue agar indicate lipase activity hydrolyzing triglycerides.
Clearing around growth on DNase agar with methyl green dye indicates DNA hydrolysis by DNase enzyme.
Complete lysis of red blood cells producing a clear zone around colonies (e.g., Streptococcus pyogenes).
Tests for sulfur reduction (black precipitate), indole production (red ring with Kovac's reagent), and motility (diffuse growth).
Yellow slant and butt indicate fermentation of glucose and lactose (and/or sucrose) producing acid.
Yellow in both tubes = oxidative and fermentative metabolism; yellow only in open tube = oxidative only; green in both = no glucose metabolism.
Reagent auto-oxidizes after 20 seconds causing false positives; early reading ensures accurate results.
Metal can break down H2O2 causing false positive bubbles unrelated to bacterial catalase.
Sensitivity relates to false negatives (missing true positives); specificity relates to false positives (incorrect positives).
H2S production requires acidic conditions; black precipitate means sulfur reduced in acidic environment.
Negative controls show baseline; positive controls confirm reagents work; known negatives check for false positives.