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MCB Lab final
Terms in this set (85)
Color of Gram +
Color of Gram Negative
Red or pink
Why is oil immersion used?
* Higher mangification
* Preserves direction of light rays
*Oil & glass have same reflective index
*Light doesn't get bent
Calculate microscope magnification:
10x for eye piece + Lens
2 systems of the microscope
* Compound light (lens + light)
* Electron microscope (beam of electrons); Has shorter wavelengths than light
What is resolving power?
Ability of the lens to distinguish fine detail & structure by the difference between 2 pts that are a specified distance apart
Why is a swab moistened?
Microbes adhere better
Why are petri dishes inverted?
Keeps condensation from dropping onto agar & spreading out or contaminating the sample
How can you tell how many types of bacteria are on a plate?
Morphology; Different colonies represent different bacteria
THings that affect inoculations:
* Insufficient nutrients
* Elapsed incubation time
What stain is used in the simple stain & how long is it applied?
Methylene blue for 1 min
Primary, Counterstain & Mordant in Gram stain?
* Primary - Crystal violet 1 min
* Counter - Saffranin 30 secs
* Mordant - Iodine 1 min
Why is flaming the loop necessary after transfer or streaking a microbe?
* Removal of previous microbes
* No contaminants
Why is heat fixing impotant?
* Kill bacteria
* Better adhesion
Gram reaction of E. coli
Gram Neg (Red)
Gram reaction of Bacillus
Gram + (Purple)
Gram reaction for Clostridium
Gram + (Purple)
Why cold old Gram + cells stain red/Gram-?
Age-weakened cell walls
Primary & counter stains in the acid-fast stain?
* Primary - Carbolfuschin
* Counter - Methylene Blue
Stains used in spore stain?
* Malachite green
Decolorizer used in Gram stain?
Decolorizer used in Acid-Fast Stain?
Acid - alcohol
Diseases diagnosed w/ acid fast stain?
Purpose of bibulous paper in acid-fast stain?
Keeps stain from drying out under steam heat
How would a 24 hr vs a 72 hr Bacillus culture differ
72 hr culture would have sporillated due to lack of nutrients
Why isn't Gram staining used for endospores?
BC the stains used in Gram staining don't penetrate the cell wall
What is the agar used in the Snyder Dental Caries test?
Snyder Test agar
Which organisms mostly affect tooth enamel?
S. mutans; Lactobacillus
Indicator used in Snyder Test?
What is the normal color of the medium used in the Snyder Test?
What color will the indicator in the Snyder test turn if the pH is more acidic? And below what pH?
Why is it generally a good rule to label the bottom of the petri plates rather than the top
BC lids fall off or twist
Why in most cases is an inoculating loop rather than an inoculating needle used for streak-plate isolations
The loop grabs and pulls the sample better; Needle would gouge the agar
What is a contaminant
Any unwanted microbe; Can come from airborne particles if the lid is left off too long
How would you determine whether a colony was a contaminant on a streak plate?
Contaminants would not be located on the streak line; Maybe a diff color or shape
What is a positive test on MSA agar?
What is negative test on MSA agar?
What is positive test on EMB agar?
Fermentation = (metallic green to pink) relative to how acidic fermentation end products are
What is negative test on EMB agar?
No change in agar
Why are bile salts and crystal violet added to MacConkey?
Bile salts inhibit non-enteric bacterial growth; Crystal violet inhibits Gram + growth to select for Gram-neg enterics
What chemicals are added to EMB to prevent Gram+ growth?
Eosin & Methylene blue (do not meet Gram+ nutritional reqs)
Differential & Selective media:
MacConkey, MSA, EMB
What makes MacConkey media selective for Gram negative bacteria?
bile salts; crystal violet
What makes MacConkey media differential for Gram negative bacteria?
Red dye & lactose for fermention
What makes MSA media selective for bacteria?
High salt concentration - selective for bacteria that tolerate high osmotic pressure
What makes MSA media differential for bacteria?
* Phenol red & sugar alcohol - pH indicators that change in the presence of acid-end products/fermentation (differentiates between coliforms & non)
What makes EMB selective for Gram negative bacteria?
Dyes Eosin & Methylene blue - inhibit growth of Gram+ bacteria
What makes EMB differential?
Lactose - when fermented causes color change (metallic green to pink) relative to how acidic fermentation end products are
What is the name for disk diffusion test?
Kirby Bauer Test
What is the name of the agar used in the disk diffusion test?
Mueller Hinton agar
Why is complete coverage of an organism on the agar important in the disk diffusion test?
to create a bacterial lawn
Is the disk diffusion test technique measuring bacteriostatic or bacteriocidal activity?
Neither. It only inhibits growth
In which growth phase is an organism most sensitive to an antibiotic?
Log/exponential growth phase
Why is the disk diffusion technique not a perfect indication of how the drug will work in vitro?
Differences in body temp; metabolism; and pH
What are the organisms used in the hemolysin test?
* Alpha - greening
* Beta - complete hemolysis/clear around cfu's
* Gamma - no change
Is the blood agar used for the hemolysin test a differential or selective medium?
What does TSI stand for?
Triple Sugar Iron
Which nutrient is in short supply in the TSI slant?
Hemolysis Test: What color will the slant and butt turn if the organism can use glucose but not lactose?
Red slant/Yellow butt
Hemolysis Test: What happens when the organism uses peptones in the agar? What color will the agar appear and why?
Protein use will form ammonia which raises pH and turns agar red/alkaline
Hemolysis Test: What happens to the color of the slant and butt if the organism can ferment lactose?
Both yellow if results are read within 10-18 hrs
Hemolysis Test: Why would the tube turn black?
Microbes that can reduce sulfur produce hydrogen sulfide gas, which reacts w iron to form iron sulfide
What is the eqn for hydrogen sulfide gas production in the hemolysis test?
H2S + Fe --> FeS + H2
Hemolysis Test: Why should you not analyze results too early?
could result in a false positive indicating that the microbe is a lactose/sucrose fermenter when it really just hasn't used up all the glucose yet
Hemolysis Test: Why should you no analyze results too late?
Causes a false negative that all sugars had been depleted
What does agar separation represent?
gas caused by fermentation
In the starch agar test what is a positive test?
clearing around the inoculated area
In the starch agar test what is a negative test?
no clearing around inoculated area
What is the chemical that is added in the starch test?
What is the enzyme that breaks down milk protein?
What is the exoenzyme in starch hydrolysis?
Is the carbohydrate test selective or differential?
differential for carb fermenters
What is an alkaline swing in the carb test?
When all sugars are depleted from the broth, pH is lowered/acidic and the indicator turns yellow. Swing occurs when the microbes start using other sources, raising the pH more alkaline and turns broth red again.
What is a positive test for fermentation in the carb test?
Yellow broth from depletion of all sugars
What is a negative test for fermentation in the carb test?
Red; no color/pH change
How does UV radiation damage bacteria
creates thiamine dimers that change the shape of the DNA & cause problems during replication
Reasons UV light isn't always effective:
* Length of exposure time
* UV doesn't kill spores like bacillus
* Have to remove lid bc UV rays won't go thru it
* Heavy bacterial concentrations can cover other microbes
What is the wavelenth that will affect/be absorbed by DNA?
254 - 260 nm
What is a positive urease production test?
Agar changes to pink/red in the presence of urease (phenol red pH indicator detects ammonia/ammonium hydroxide)
What is the source of urea in the body?
protein catabolism in the liver
What is the formula for urea hydrolysis
Urea ----> 2NH3 + CO2
Is the test for milk qualitative or quantitative?
quantitative; bacterial counts
Milk is considered contaminated when the bacteria count rises above what number?
What will happen if the agar is too hot when mixing the organisms from the dilutions?
Heat could kill the bacteria
Range of bacterial colonies required?
25 - 250 CFU's
THIS SET IS OFTEN IN FOLDERS WITH...
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