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BIO 150 Lab Exam 2
Terms in this set (67)
what is the optimal temperature for growth of E. coli?
30 C or room temperature
what is the optimal temperature for growth of S. marcescens?
because bacteria are adapted to different temperatures and produce different enzymes
why do different temperatures produce different growth rates?
to check for the presence of dental carie-causing bacteria
what is the purpose of the snyder test?
yellow = positive; green = negative
interpret the results of the snyder test
snyder test contains bromcresol green (indicator) and lactobacilli and streptococci ferment sugar and make the medium more acidic (changes to yellow)
explain why the color of the snyder test medium changes from green to yellow
casein hydrolysis and fermentation of glucose
considering the snyder test ingredients, suggest other metabolic functions that Lactobacilli might perform
starchy foods, sweets, corn syrup, processed foods
what kinds of dietary items would increase the number of lactobacilli in saliva?
1. so you can mix the saliva in the medium
2. lactobacilli are facultative anaerobes
3. if we inoculate on a solid surface, the bacteria will grow aerobically and will not ferment the sugar
why isn't the molten snyder test agar allowed to solidify as a slant?
non-ionizing, long wavelength
is UV light ionizing or non-ionizing? short or long wavelength?
which is more germicidal - long or short wavelength?
UV-C because it has more energy
which wavelength of UV light is most germicidal? Why?
makes thymine dimers
how does UV light cause death of microbes?
have photolyases that repair thymine dimers
what limited protection do cells have against the damaging effects of UV radiation?
they have a hard-coating that can't be penetrated
how are endospores protected from the harmful effects of UV light?
stationary phase because it will have produced endospores
which B. megaterium culture, log or stationary phase, would show the best survival following exposure to UV radiation? why?
1. alpha (partial hemolysis)
2. beta (complete hemolysis)
3. gamma (no hemolysis)
define the 3 major types of hemolysis that can be seen on blood agar
1. alpha - blackening + colonies
2. beta - red + clearing
3. gamma - red + colonies
describe the results of hemolysis by looking at the inoculated blood agar plates
name the exotoxin produced by Gram + cocci that can cause breakdown of red blood cells
what type of hemolysis is produced by Streptococcus pyogenes, the causative agent of strep throat?
what type of hemolysis is produced by Streptococcus pneumoniae?
because you don't want to spread infectious bacteria
assuming that al of the organisms cultivated in the blood agar exercise came from the throats of healthy students, why is it important to cover and tape the plates?
what is the name of the agar used in the filter paper disk method?
from one side of the zone of inhibition to the other
how do you measure the zone of inhibition from the filter paper disk method?
what is the best disinfectant/antiseptic used in lab for all of the bacteria?
mouthwash & bleach
which were the 2 least effective disinfectant/antiseptics used in lab for the bacteria?
antiseptics - used on living tissue
disinfectants - used on non-living surfaces
what is the difference between antiseptics and disinfectants?
give an example of an antiseptic
give an example of a disinfectant
they do not kill microbes, they lower their numbers
how do sanitizers work?
bacteriostatic - inhibits growth
bactericidal - kills microbes
difference between bacteriostatic/bactericidal?
to determine if a bacteria grows aerobically or if they ferment sugar with the production of acidic and gaseous by-products when added to a medium with lactose or glucose as the sole carbohydrate
what is the purpose of the fermentation test?
1. yellow + gas bubbles = fermentation (positive)
2. red/pink (no change in color) = no fermentation (negative)
describe the possible results from the fermentation test?
ferments = E. coli (fac. anaerobe)
non-ferment = P. aeruginosa (oblig. aerobe)
list a fermenting bacteria and a non-fermenting bacteria
phenol red (indicator), lactose/glucose, and an inverted vial
list 3 items found in the fermentation test
to determine the production of hydrogen sulfide gas
what is the purpose of kligler's test?
gram - enteric bacteria
what is Kligler's test most useful for differentiating?
glucose, lactose, peptone, and iron salts
what does Kligler's agar contain?
what is the indicator in Kligler's test?
yellow = fermentation
yellow at bottom, black in middle, pink at the top = hydrogen sulfide produced
describe the results of Kligler's test
S. typhimurium (salmonella) = yellow, black, pink
E. coli = most is yellow
E. faecalis = yellow
list 3 bacteria used for Kligler's test and their results
isolation using EMB agar
which test should you use to differentiate between E. coli and E. faecalis?
it determines if a bacteria uses citrate as a sole carbon source during oxidative metabolism; also creates an alkaline environment
what is the purpose of the citrate test?
what is the indicator used in the citrate test?
blue = positive (uses citrate)
green = negative (no change in color)
describe the results of the citrate test
1. positive (blue) = E. cloacae & S. typhimurium
2. negative (green) = E. coli
name bacteria that test positive and negative in citrate test
for isolating gram - intestinal bacteria
what is the EMB agar used for?
it contains lactose and a dye so that if an organism is a lactose fermenter, its colony will take on a color characteristic of the dye present
how does the Eosin-Methylene Blue agar work?
1. E. coli = green metallic color (strongly ferments)
2. E. cloacae = dark pink (weak ferments)
3. S. typhimurium = light pink (weak ferments)
list 3 bacteria used in EMB isolation and their appearance on the plate
Mannitol Salt Agar plate
which lab should you do if your bacteria is cocci?
which type of bacteria is identified using MSA?
it is a selective medium for gram + bacteria that can tolerate salt (staph vs strep) and a differential medium (s. aureus vs s. epidermidis)
what is the purpose of the MSA test?
s. aureus = gold plate + gold colonies (ferments)
s. epidermidis = pink plate + pink colonies (grows aerobically)
list the 2 bacteria used in MSA test and their appearance/results
determines which bacteria produce enzymes (proteases) that can degrade proteins
what is the purpose of the Gelatin Stab test?
B. subtilis = liquified (positive for enzyme)
E. coli = solid (negative)
list 2 bacteria used in Gelatin Stab test and their appearance/results
gram - bacteria
which type of bacteria is best used in the catalase test?
to determine which bacteria produce the enzyme, Catalase
what is the purpose of the Catalase test?
staph vs strep
name 2 bacteria in which the catalase test will help differentiate
3% hydrogen peroxide
what is used in the catalase test?
S. aureus = bubbles (positive for catalase)
S. faecalis = no bubbles (negative)
list the 2 bacteria used in the Catalase test and their appearance/results
inoculate bacteria into a tube of glucose and a tube of lactose broths, containing inverted vials
list procedure of the Fermentation test
streak on the slant, then stab the deep part using same needle
list procedure of Kligler's test
streak on the slant, then stab the agar using same needle
list procedure of the citrate test
use quadrant streak method
list procedure of the EMB plate
use quadrant streak method
list procedure of the MSA plate
inoculate tube and stab the test tube straight down with a straight needle; on NEXT lab: place in ice water for 15 minutes, then tilt the tube several times from side to side to check for liquefaction
list procedure of the gelatin stab test
inoculate nutrient agar slant with bacteria; NEXT lab: using a pipette, dribble 3% hydrogen peroxide over the culture
list procedure of the catalase test
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