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practical bio
| Question | Answer |
|---|---|
| What is the main purpose of aseptic technique? | To prevent contamination of cultures, media, and the environment by unwanted microorganisms. |
| Why is aseptic technique important in a clinical lab? | It ensures reliable results and prevents pathogen spread to the handler or environment. |
| What is the goal of a T-streak or quadrant streak plate? | To isolate individual colonies from a mixed culture. |
| What causes poor isolation on a streak plate? | Not flaming the loop between sections, overlapping streaks, or picking up too much inoculum. |
| What does “colony morphology” describe? | The visible traits of colonies—shape, margin, elevation, texture, color, and size. |
| What does multiple colony types on one plate indicate? | Possible contamination or a mixed culture. |
| What is a general-purpose medium? | upports growth of most non-fastidious organisms (e.g., Nutrient Agar). |
| What is an enriched medium? | Contains added nutrients for fastidious organisms (e.g., Blood Agar). |
| What is a selective medium? | Contains ingredients that inhibit some microbes while allowing others to grow. |
| What is a differential medium? | Contains indicators that distinguish between microbial types based on metabolism. |
| What does MSA select for? | Salt-tolerant (halotolerant) organisms, especially Staphylococcus spp. |
| What does a yellow MSA plate mean? | The organism ferments mannitol (acid production → phenol red → yellow). |
| What does EMB select for and differentiate? | Selects Gram-negative bacteria; differentiates lactose fermenters (purple/green) from non-fermenters (colorless). |
| What causes a metallic green sheen on EMB? | Strong lactose fermentation by E. coli. |
| What does MacConkey Agar (MAC) select for? | Gram-negative enteric bacteria; differentiates lactose fermenters (pink colonies). |
| What enzyme does the DNAse test detect? | DNase—an enzyme that hydrolyzes DNA. |
| How do you visualize a positive DNAse test? | A clear halo forms after adding hydrochloric acid (HCl). |
| What enzyme is detected in the starch hydrolysis test? | Amylase |
| What reagent is added in the starch test, and what indicates a positive result? | Iodine (potassium iodide); a clear zone around growth shows starch hydrolysis. |
| What enzyme does the casein hydrolysis test detect? | Casease—breaks down milk protein casein; clear zone = positive. |
| What is the purpose of the Kirby-Bauer test? | To measure bacterial susceptibility to antibiotics. |
| What medium is used for the Kirby-Bauer test? | Mueller-Hinton Agar. |
| What does a large zone of inhibition indicate? | The organism is more susceptible to that antibiotic. |
| How is the result interpreted? | Using an interpretation chart comparing diameter (mm) to R/I/S categories. |
| Why is a standardized streak pattern used? | o create a uniform bacterial lawn for consistent diffusion. |
| What does “spectrum” mean in antibiotics? | The range of microbes an antibiotic targets (broad vs. narrow). |
| What is total magnification? | Ocular × Objective magnification (e.g., 10× × 100× = 1000×). |
| What is the purpose of immersion oil? | Reduces light refraction and increases resolution at 100× objective. |
| Which knob should you use with 40× and 100× objectives? | Only the fine adjustment knob. |
| What could cause a dark field of view? | Light intensity too low or diaphragm closed. |
| What does a simple stain show? | Shape (morphology) and arrangement of cells. |
| What are common bacterial shapes? | Coccus (round), Bacillus (rod), Spirillum (spiral). |
| What does “Gram-positive” mean? | Cells retain crystal violet and appear purple due to thick peptidoglycan. |
| What does “Gram-negative” mean? | Cells lose crystal violet and stain pink with safranin; thin peptidoglycan + outer membrane. |
| What’s the difference between positive and negative stains? | Positive stains color the cells; negative stains color the background. |
| Why do we heat-fix slides? | To kill and adhere cells to the slide. |
| What can happen if you overheat a slide while fixing? | Distorts or lyses the cells. |
| What are the five CDC steps of handwashing? | Wet → Lather → Scrub → Rinse → Dry. |
| Which is more effective—hand sanitizer or washing? | Handwashing removes debris and some microbes sanitizer can’t; sanitizer is bactericidal but less effective on soiled hands. |
| What is a common experimental error in the handwashing lab? | Unequal contact time, touching surfaces after washing, or inconsistent sampling. |
| What is “Patient Zero”? | The initial individual who began an outbreak. |
| What is direct transmission? | Person-to-person contact. |
| What is indirect transmission? | Via contaminated objects (fomites). |
| What is vector transmission? | Spread through insects or animals carrying pathogens. |
| What is a portal of entry? | Site where microbes enter the body (respiratory, GI, skin, urogenital). |
| What is a portal of exit? | Route pathogens leave (saliva, feces, blood, secretions). |
| What range of colonies is considered “countable”? | 30–300 colonies per plate. |
| How is CFU/mL calculated? | CFU ÷ (dilution × volume plated). |
| What does spread plating use? | A sterile “hockey stick” to evenly distribute liquid inoculum. |
| What’s the main difference between streak and spread plating? | Streak isolates colonies; spread provides quantifiable growth. |
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