MIC Lab Final Review Flashcards
(40 cards)
Lab etiquette
Wash hands, wipe bench, locate showers, coat and goggles, long pants and no food or drink
Define contamination
When a microorganism gets into your experiment and ruins it
What are the 3 types of contamination and what do they mean?
Chemical - the presence of harmful chemicals or toxins (pesticides in fruit)
Biological - presence of microorganisms like bacteria, virus, or fungi (salmonella in contaminated food)
Physical - the introduction of foreign objects (glass shard in a beverage)
What is the difference between transient and resident flora?
Resident lives within (and on) us - normal flora
Transient is foreign to us - generally can cause infections
What is the difference between a control and experimental variable?
Variable staying the same throughout a trial vs. variable being tested
What is the order of how to set up and use a microscope?
- Start with 4x lens and focus
- Move to 10x lens and only focus with fine adjustment
- Focus with 40x
- Rotate objective lenses halfway to add drop of oil to slide
- Rotate to 100x and focus
What is the purpose of aseptic technique?
Protect yourself and limit introduction of environment contaminants
Describe aseptic technique
Flame inoculating loop until red hot before and after each use as well as the lid of the tube being handled when handling cultures. Work close to the Bunsen burner
What is the equation for serial dilutions?
Original inoculum = CFU / (volume plated x dilution)
When using serial dilutions, how do you choose which plate to use for the serial dilution equation?
The one with 30-300 colony forming units
Dilution = ?
10^-(whatever that tube is -1)
example: tube is 10^-1 so that plate is 10^-2 then the next tube is also 10^-2 and plate is 10^-3
Why does gram-positive bacteria turn purple? And gram-negative pink?
When the ethyl alcohol attempts to decolorize a gram-positive bacteria, the peptidoglycan becomes dehydrated, physically shrinks, and becomes impermeable locking the purple stain inside the cell.
When the alcohol comes in contact with a gram-negative cell wall the lipids are dissolved and the crystal violet is leached out of the cell.
What is the difference in cell wall between gram-positive and gram-negative bacteria?
The gram-positive cell wall is think and composed of many layers of peptidoglycan
The gram-negative cell wall has a simple layer of peptidoglycan surrounded by layers of various types of lipids
What are the 4 steps of a gram stain and their purposes?
The primary stain - crystal violet and turns all bacteria purple
The mordant - causes a stain to become more tightly bound to the cell (grams iodine intensifies the ionic chemical bond between crystal violet and the bacteria)
The decolorizer - ethyl alcohol, removes stain from gram-negative
The counterstain - safranin stains colorless cells (gram-negative)
What is the difference between bactericidal and bacteriostatic?
Bactericidal: agents that kill bacteria
Bacteriostatic: agents that prevent new growth, keeping bacteria in a stationary phase
What is the purpose of disinfectants?
Chemical agents that kill or control microbes on inanimate surfaces
What are factors that contribute to resistance of disinfectants?
- Spore-forming capabilities
- Thick protective outer membranes
- Presence of lipid capsules
What do antibiotics do?
Kill or control microbes in living bodies (overuse can lead to resistance)
What is natural selection in bacteria?
Bacteria develop resistance over time
Resistant strains thrive, non-resistance strains decline
A larger zone of inhibition indicates stronger resistance)
What type of medium is a Mannitol Salt Agar and what is its purpose?
Selective and Differential medium for Staphylococcus
Selective medium
- High salt concentration selects mainly for Staphylococcus genera
- Salt-intolerant organisms can’t grow
Differential medium
- Staphylococcus aureus ferments mannitol (sugar) and changes the color from red to yellow
- Staphylococcus epidermidis does not ferment mannitol and does not change the color but instead grows
Describe a blood agar and what it tests for
Enrichment medium - provides additional nutrients for certain fastidious microbes; does not inhibit others
Differential medium - used to characterize many species of streptococcus based on reaction on blood agar
- Beta-hemolysis - complete lysis of red blood cells leading to clear zone around growth (S. pyogenes)
- Alpha-hemolysis - greenish zone around growth (S. viridans and S. pneumoniae)
- Gamma-hemolysis - no effect on media (S. salivarius and S. agalactiae)
What is the Lancefield system of antigens?
A way to distinguish species within the genus Streptococcus (grouped A-R) based on antigens in the cell
What is group A sensitive to in the Lancefield system?
Bacitracin (S. pyogenes)
What is S. pneumonia sensitive to?
Optochin (P-test; zone of inhibition)
