Quiz 2 Discussion - Practice Questions for review on chapters based on the exam. R. Wong PDF

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Lab Quiz DiscussionTrue or false? The Turbidity method is a direct method in bacterial population counts because the bacterial colonies can be counted. The correct answer is FALSE. The Turbidity method is an indirect method because it is only measuring how cloudy the culture might be. Standard plate...

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Lab Quiz Discussion True or false? The Turbidity method is a direct method in bacterial population counts because the bacterial colonies can be counted. The correct answer is FALSE. The Turbidity method is an indirect method because it is only measuring how cloudy the culture might be. Standard plate count, however, is a direct method because it is counting the number of bacterial colonies.

In Standard Plate Count, the first test tube is not diluted, so its dilution factor is: a/ 104 b/ 103 c/ 102 d/ 101 e/ 100 That is right! Whenever you see the exponent is a zero, it means that this culture or solution is NOT diluted and has a 1:1 ratio. Only when you see at least a 1 or more as the exponent, then you know that culture is diluted. If the dilution factor of a culture is 104, it can be expressed as: a/ 1:1,000,000 b/ 1:100,000 c/ 1:10,000 d/ 1:1,000 e/ 1:100 Correct! The exponent indicates the number of zeros in the dilution factor, and in this case there should be 4 zeros: 1:10,000 dilution.

In Standard Plate Count, if the number of the colonies is 196, the actual number to be used in the calculation should be: a/ 200 b/ 196

c/ 190 d/ 150 e/ 100 That is right! When counting the colonies, it is believed that the number is never exactly accurate due to human error, so by convention we always round off the number. If the last digit at the right is 5 or above, then we round up. If the last digit is less than 5, then we round down. In this case, 196 should be rounded off to be 200 for the calculation.

For a culture with a dilution factor of 103, if the number of colonies is 323, then the number of bacteria/ml would be: a/ 323,000 b/ 300,000 c/ 32,300 d/ 30,000 e/ 320,000 The correct answer is 300,000. Some of you might be thinking that it should be 320,000 bacteria/ml. But by convention we never consider any bacterial colony counts above 300 to be accurate because the human eyes will become fatigue after counting too many colonies. So any numbers above 300 would be reduced to 300 only. In this case, 323 ---> 300, and 300 x 1,000 dilution factor = 300,000 bacteria/ml.

For a culture with a dilution factor of 105, the number of colonies is 78, thus the number of bacteria/ml would be: a/ 10,000,000 b/ 8,000,000 c/ 7,800,000 d/ 7,500,000 e/ 7,000,000 Correct! The number of colony is less than 300, so we don't need to worry about the 300 limit. 78 is rounded up to be 80, and 80 x 100,000 dilution factor = 8,000,000 bacteria/ml.

In the Turbidity method, a less cloudy culture should have a/an _____ %T. a/ higher b/ lower c/ identical The correct answer is Higher. When a culture is not cloudy, more light can pass through it in the spectrophotometer, resulting in a higher %T figure. And vice versa is true: more cloudy culture = lower %T.

In the Turbidity method, a more cloudy culture should have a/an _____OD. a/ higher b/ lower c/ identical The correct answer is Higher. Keep in mind that the OD (optical density) is in proportion with the cloudiness of a culture. So a more cloudy culture should have a higher OD. And vice versa is true: a less cloudy culture = lower OD.

In the Turbidity method, the first test tube should have a dilution factor of: a/ 1:16 b/ 1:8 c/ 1:4 d/ 1:2 e/ 1:1 That is right! The 1:1 dilution, of course, means that this culture is NOT diluted. This test tube is used to "teach" the spectrophotometer what a undiluted culture looks like, so that it can compare it to the diluted cultures in other test tubes. The 1:1 tube should have a low %T and high OD because it is very cloudy.

In the Turbidity method, we only had 5 test tubes, what would be the dilution factor if we added one more test tube at the end? a/ 1:4 b/ 1:8

c/ 1:16 d/ 1:32 e/ 1:64 That is right! In the Turbidity method, we dilute each test tube by 2 folds, and that is why we see the dilution factors as 1:1, 1:2, 1:4, 1:8, and 1:16. If another tube of culture is made, it should be 1:32 (twice as diluted as the 1:16 tube).

If %T is 45, what is OD? a/ 1.653 b/ 1.346 c/ 0.346 d/ 0.653 e/ 0.259 Correct! The formula is OD = 2 - log%T. Log of 45 is 1.653, and when it is subtracted from 2, the result is 0.346. Be sure you practice this formula on your calculator app and know which button is for the log function. Let's move on to the Antiseptics and Antibiotics labs.

Antiseptics kill microbes on the ____ while disinfectants kill microbes on ____. a/ body, nonliving things b/ nonliving things, body c/ viruses, bacteria d/ protozoa, helminths That is right! Antiseptics are not poisonous to human cells, so they are safe to be used on the body (eg. alcohol in hand sanitizer), while disinfectants like chlorine is poisonous to human cells, so they can only be used on nonliving things.

The specialized medium used in the Effectiveness of Antiseptics lab was: a/ Citrate agar

b/ Tryptone broth c/ Trypticase soy agar d/ Nutrient gelatin e/ Mannitol salt agar Answer: Trypticase soy agar. Trypticase soy agar (TSA) was developed to grow common bacteria found on the human body and in our surrounding area. When bacterial colonies appear on TSA, they would indicate how well an antiseptic might be by measuring the Zone of Inhibition.

If an antiseptic or antibiotic drug is not effective, the Zone of Inhibition should be ____: a/ larger b/ smaller Correct answer is Smaller. The smaller the zone of inhibition is, the less effective this antiseptic or antibiotic drug might be. This is how the FDA is able to compare the effectiveness of all antiseptics and antibiotic drugs and make recommendations to the general public and hospitals. Let's move on to the Staphylococci lab.

The specialized medium used in the Staphylococci lab was ____ which allowed ____ bacteria to grow well: a/ Citrate agar, acidophilic b/ Tryptone broth, halophilic c/ Trypticase soy agar, thermophilic d/ Nutrient gelatin, alkalophilic e/ Mannitol salt agar, halophilic Correct! Mannitol salt agar (MSA) is a unique medium for Staphylococci. Mannitol is a sugar that some Staphylococci might utilize for their metabolism, while salt (NaCl) is a common chemical requirement for all Staphylococci ("halo" refers to salt, "philic" means to love).

MSA would turn ____ (yellow/red) if the bacteria can ferment mannitol sugar, and the color change is due to a ____-sensitive dye added in MSA:

a/ Yellow, heat b/ Red, heat c/ Yellow, pH d/ Red, pH e/ Yellow, salt That is right! Bacteria like Staphylococcus aureus can metabolize mannitol, resulting in the release of acids which change the color from red to yellow in MSA. The pH-sensitive dye added in the agar is to detect the presence of the acids from mannitol fermentation.

The bacterium in the Staphylococci lab’s video that did NOT change color in MSA was: a/ Streptococcus pyogenes b/ E. coli c/ Staphylococcus aureus d/ Proteus vulgaris e/ Staphylococcus epidermidis Correct answer is Staphylococcus epidermidis. Only Staphylococci bacteria are able to survive in MSA due to its high-salt content. And only Staphylococcus aureus is able to metabolize mannitol and release acids, changing MSA to yellow. Staphylococcus epidermidis survives in MSA but is unable to utilize mannitol, resulting in no color change. Let's move on to the Streptococci lab.

In the Streptococci lab, ___-hemolytic streptococci cause complete lysis of red blood cells, resulting in a ____ zone around the colonies: a/ Alpha, green b/ Beta, clear c/ Gamma, clear d/ Alpha, clear e/ Beta, green

The correct answer is Beta, clear zone. Only beta-hemolytic Streptococci are able to release the beta-hemolysin enzyme which completely breaks down red blood cells in the blood agar plate, causing a clear zone around the colony.

In the Streptococci lab, ____- hemolytic streptococci reduce ____ to methemoglobin, resulting in a green zone around the colonies: a/ Alpha, hemoglobin b/ Beta, hemoglobin c/ Alpha, proteinase d/ Beta, lipase e/ Alpha, nucleic acids Correct! Alpha-hemolytic Streptococci can release the alpha-hemolysin enzyme which reduces hemoglobin (the protein in red blood cells for binding to oxygen) to methemoglobin, resulting in a green/brownish zone around the colony.

Gamma hemolysis indicates the ____ of hemolysis, and after 24 hours it would turn to ____ hemolysis: a/ Highest level, alpha b/ Lowest level, beta c/ Lack, alpha d/ Lack, beta e/ Lack, delta That is right! Scientists named the third type of hemolysis gamma, just to clarify that it is possible for some Streptococci not to show alpha or betahemolysis immediately. This lack of hemolysis would turn into an alphahemolysis after 24 hours. Let's move on to the Unknown lab.

What is this unknown bacterium? a/ Gram+ cocci, clusters b/ Gram+ bacilli, chains c/ Gram- cocci, singles d/ Gram- cocci, clusters e/ Gram- bacilli, singles Correct! If you recall from Gram staining, Gram+ is purple while Gram- is pink. In this case, the unknown is Gram- cocci, singles, because it doesn't show any cell arrangements like clusters or chains.

What is this unknown bacterium?

a/ Gram+ cocci, clusters b/ Gram+ bacilli, chains c/ Gram- cocci, singles d/ Gram- cocci, clusters e/ Gram- bacilli, singles That is right! The purple color, elongated cell shape, and chains of bacteria would indicate that this unknown must be Gram+ bacilli in chains.

True or false? This unknown is motile Correct! This medium called Semisolid medium would change to a purple color when the unknown is motile. If the unknown is nonmotile, it won't change color and we can only see a streak of bacteria in the center of the medium.

True or false? This unknown in the bottom test tube shows nutrient gelatin liquefaction. That is right! Some bacteria are able to release an enzyme called gelatinase that breaks down the nutrient gelatin in this test tube, causing it to be in a liquefied state. For bacteria that are lacking this enzyme, the test result would show a solidified state.

If citrate utilization test is positive, the color should be ____: a/ Green b/ Blue c/ Orange d/ Red e/ Clear (colorless) The correct answer is Blue. The original color of the Simmon's Citrate agar slant is green, and when bacteria are able to utilize citrate, it would change to blue.

Many chemical tests in the unknown project, such as the Indole, Nitrate, and Urease tests, show the ____ color when the result is positive: a/ Green b/ Blue

c/ Orange d/ Red e/ Clear (colorless) That is right! It is not by accident that many chemical tests turn red, simply because it is a bright color to indicate a positive result.

When the Litmus Milk test shows the pink color, it indicates ____: a/ Alkaline b/ Acid c/ Neutral d/ Halophilic e/ Thermophilic Correct! Similar to the MSA plate that has a pH-sensitive dye, the Litmus Milk also contains a dye that changes to pink when acid is detected. If there is no acid, it remains purple for being alkaline.

Cells are cocci Gram positive Aerobic, glucose fermentation negative yellow pigment....................................................Micrococcus luteus red pigment.........................................................Micrococcus roseus Facultative, glucose fermentation positive mannitol is positive..............................................Staphylococcus aureus mannitol is negative.............................................Staphylococcus epidermidis Gram negative Pigment in culture....................................................Neisseria subflava No pigment in culture glucose is positive.............................................Neisseria sicca glucose is negative...........................................Neisseria flavescens

If an unknown is Gram+ cocci, facultative, and can ferment glucose and mannitol, it must be: a/ Micrococcus roseus b/ Staphylococcus aureus c/ Neisseria subflava d/ Staphylococcus epidermis e/ Micrococcus luteus Correct! Always remember that the key-out chart is designed like the fork at the end of a road, meaning that you can only choose one path each time. Once you have selected a choice, you need to ignore the rest of the chart and proceed only along that path. In this case, if you follow the Gram+ cocci, facultative, glucose+, and mannitol+ path, you will end up with Staphylococcus aureus.

Cells are bacilli Gram positive Endospores Mannitol fermentation positive Voges-Proskauer positive..................................Bacillus subtilis Voges-Proskauer negative...............................Bacillus megaterium Mannitol fermentation negative..............................Bacillus cereus No endospores glucose fermentation positive...............................Lactobacillus fermentum mannitol fermentation positive.............................Lactobacillus casei mannitol fermentation negative............................Lactobacillus lactis

If an unknown is Gram+ bacilli without endospores and can ferment mannitol, it must be: a/ Bacillus megaterium b/ Lactobacillus lactis c/ Bacillus subtilis d/ Lactobacillus casei e/ Lactobacillus fermentum That is right! During the lab quiz next week, you don't need to memorize the key-out chart because it will be shown on the question like today's review. If you followed the path near the bottom of the chart given, you would end up with Lactobacillus casei. Let's move on to the Vaccine lab.

Andrew Wakefield published a fraudulent paper in 1998 linking autism to the ____ vaccine: a/ Polio b/ Influenza c/ MMR d/ Hepatitis A e/ Varicella Correct! The paper was based on a small study with only 12 patients, and not all of them had autism! The year 1998 was also the beginning of the wide-spread use of the Internet, which allowed this myth about vaccines causing autism to spread like a wild fire. Today many people still believe that vaccines are harmful to the population.

The first vaccine discovered by Jenner in the 18th century successfully treated _____: a/ Influenza b/ Measles c/ Hepatitis B d/ Cowpox

e/ Bacterial meningitis That is right! In fact, the word "vaccine" refers to the cows in Latin. This vaccine was later used to treat smallpox and was equally successful....