microbio lab exam 2
Rotten Eggs
Hydrogen sulfide gas has a characteristic odor that is similar to what smell?
Why is E. coli a good test bacteria for fecal contamination in water?
It is only found in human intestines, not soil or water; easily identified; last longer in water samples than intestinal pathogens
A student is counting the number of bacteria in a sample. She uses two methods: Counting bacterial cells with a microscope and A plate count method using serial diluted sample. Why does the plate count have an advantage? A student is counting the number of bacteria in a sample. She uses two methods: Counting bacterial cells with a microscope and A plate count method using serial diluted sample. Why does the plate count have an advantage? It takes into account only viable cells. It uses fewer materials. The procedure is less time consuming. There is much less likelihood for error.
It takes into account only viable cells.
Why do we use the term colony-forming units, instead of cells, when expressing concentration of bacteria in a sample? Why do we use the term colony-forming units, instead of cells, when expressing concentration of bacteria in a sample? There could be different species of bacteria in the sample. Not all cells are viable. Sometimes a group of cells forms a single colony. Only the colonies on the upper surface of the agar are counted.
Sometimes a group of cells forms a single colony.
Two different bacterial samples, A and B, were inoculated onto MacConkey agar. What can you conclude based on your observations? Based on your observation of the pictured MacConkey agar plates, select ALL appropriate conclusions.
Specimen A is able to ferment lactose Specimen A is most likely Gram-negative Specimen B is most likely Gram-negative
Part D Enriched blood agar permits the demonstration of the hemolytic properties of what group of microorganisms?
Streptococci
Why must you perform multiple dilutions for each food type? You need to get one TFTC plate, one countable plate, and one TNTC plate for each food. You do not know if the organisms in the food are Gram positive or Gram negative. You do not know if the organisms in the food are pathogenic. You do not know the initial concentration of bacteria in the food.
You do not know the initial concentration of bacteria in the food.
What is the positive result of a lactose fermentation test for coliform bacteria?
acid production (yellow color) + 10% or more of tube filled with gas in 48 hours
Describe the completed test
agar slant with lactose broth is inoculated from isolated colony on EMB agar and gram stain is performed to confirm morphology
Urease hydrolyzes urea, releasing
ammonia
Describe the presumptive test for coliform presence?
bacteria grown in lactose broth in durham tubes for 48 hours, 3 different dilutions of water samples for testing (10, 1, 0.1 ml)
When bacteria use citrate, the medium becomes alkaline, and the bromthymol blue indicator will be
blue
Which of the following is indicative of the presence of E. coli? colonies on EMB agar with a metallic sheen colonies on EMB agar with a white precipitate inhibited growth on EMB agar growth on EMB agar
colonies on EMB agar with a metallic sheen
What is the next step after a positive confirmation test result (3rd step)?
completed test
What is the next step after coliforms are presumed to be present (2nd step)?
confirmation test
Differential media are used to
distinguish among morphologically and biochemically related groups of organisms
What is a positive result for coliform bacteria in a MacConkey agar?
fermenting bacteria drop ph of agar and changes its color to pink, or reddish color
If a bacterium produces urease, the phenol red indicator will turn
fuchsia
What is a positive result for coliform in a completed test?
gas production in broth + gram - non spore forming rods
Are the two coliform bacteria gram - or +? aerobic or anaerobic? spore forming or non spore forming? morphology?
gram -; facultative anaerobic; non spore forming; rods
What characteristics does MacConkey agar have to help test for coliform?
inhibits gram + bacteria growth; differentiates between lactose fermenting and non lactose fermenting gram - bacteria
What sugar is fermented in the first test for determining presence of coliform bacteria?
lactose
What provides the basis for determining the MPN of coliform in a sample?
lactose fermentation
An uninoculated urea agar slant is yellow, indicating that the pH is
less than 7
Helicobacter pylori, a pathogen of the stomach, produces a powerful urease. Why might urease be a useful enzyme for this microbe?
make's the cell environment more alkaline
Partial nitrate reduction results in the formation of...
nitrite & water
In the nitrate reduction test, only after the addition of zinc to your 24-hour incubated solutions A and B is there a color change. What does this indicate?
no nitrate was reduced by bacteria
What is a positive result for a confirmation test on EMB agar? Endo agar?
nucleated colonies; reddish colonies
The indicator in urea agar is...
phenol red
If the presumptive test is positive than it is _______ that coliforms are present.
presumed
What is the first test for testing for coliform bacteria in a water sample?
presumptive test
After incubation, a citrate test for Escherichia coli is green. What is the best explanation for this result?
the bacteria did not ferment the citrate
If no color change after addition of zinc
the nitrate had been reduced completely to ammonia
Citrate agar tests for...
use of citrate by bacteria
In the nitrate reduction test, you mistakenly add the zinc powder before the addition of solutions A and B. Will this change your results and why?
yes, it possible it will reduce both solution
A specimen was inoculated onto the MacConkey agar pictured here. Based on your observation of the pictured MacConkey medium, select ALL appropriate conclusions . (Recall that an observation and a conclusion are different. An observation is simply what you see; conclusions are statements of what you learned from your observations.)
*The bacteria ferments lactose* *The bacterium is most likely Gram-negative* *The bacteria grew*
Arrange the steps to correctly arrive at an estimate of the quantity of bacteria in a sample of a solid food. Do not overlap any steps.
- Weigh 1g of sample and place into 9ml of sterile water. -Prepare serial dilutions of the sample. -Deliver inoculum to each plate. -Pour melted agar into plates. -Stack plates, invert, and incubate. -Count colonies and calculate concentration.
What color would colonies of a non-fermenter, such as Salmonella typhimurium, be on MacConkey agar?
Non-lactose fermenters do not produce acid, and their colonies appear tan and frequently colorless.
Item 2 Flagella arrangement Part A Observe the micrograph and draw conclusions about the pictured bacterium. http://session.masteringmicrobiology.com/problemAsset/1556479/1/Flagella_05.jpg Based on your observation of the bacterium in this micrograph, select ALL appropriate statements. The indicated bacterium has a monotrichous flagella arrangement. The indicated bacterium has cilia. The indicated bacterium is motile. The indicated bacterium has a lophotrichous flagella arrangement. The indicated bacterium has a peritrichous flagella arrangement. The indicated bacterium has an amphitrichous flagella arrangement.
1) The indicated bacterium is motile. 2)The indicated bacterium has an amphitrichous flagella arrangement.
Two specimens, A and B, were inoculated into Urea broth. What can you conclude from your observations? http://session.masteringmicrobiology.com/problemAsset/1556524/2/Urea_test_07.jpg Based on your observation of the pictured Urease tests, select ALL appropriate statements. Bacterium A ferments lactose Bacterium A converted urea to ammonia Bacterium A increased the pH of the medium Bacterium B ferments lactose Bacterium B converted urea to ammonia Bacterium B decreased the pH of the medium Bacterium B does not produce urease
1)Bacterium A converted urea to ammonia 2)Bacterium A increased the pH of the medium 3)Bacterium B decreased the pH of the medium 4)Bacterium B does not produce urease
What can you conclude about the pictured bacteria? http://session.masteringmicrobiology.com/problemAsset/1556520/1/Endospores_07.jpg If a Gram stain was performed on this bacterium within 24 hrs of a fresh culture, it would most likely be Gram-positive. The pictured bacteria are bacilli The indicated structure is used for reproduction The indicated structure is a vacuole The indicated structure is a nucleus The pictured bacteria are cocci The indicated structure is an endospore
1)If a Gram stain was performed on this bacterium within 24 hrs of a fresh culture, it would most likely be Gram-positive. 2)The pictured bacteria are bacilli 3)The indicated structure is an endospore
Interpreting Simmons Citrate tests Two different bacterial samples, A and B, were inoculated onto Simmons Citrate agar. What conclusions can you make? http://session.masteringmicrobiology.com/problemAsset/1556532/1/Citrate_test_08.jpg Based on your observation of the pictured citrate media, select ALL appropriate conclusions. Specimen A cannot use sodium citrate as a carbon source Specimen A can use sodium citrate as a carbon source Specimen A raised the pH of the medium as a result of its metabolic processes Specimen B cannot use sodium citrate as a carbon source Specimen B can use sodium citrate as a carbon source Specimen B raised the pH of the medium as a result of its metabolic processes
1)Specimen A can use sodium citrate as a carbon source 2)Specimen A raised the pH of the medium as a result of its metabolic processes 3)Specimen B cannot use sodium citrate as a carbon source
Two different bacterial samples, A and B, were tested with an Oxidase dry slide. This is a picture of the test results. http://session.masteringmicrobiology.com/problemAsset/1556554/1/Oxidase_dry_slide_02.jpg Select ALL appropriate statements regarding the pictured Oxidase test results. Specimen A fermented cytochrome oxidase. Specimen A produces cytochrome oxidase. Specimen A does not produce cytochrome oxidase. Specimen B fermented cytochrome oxidase. Specimen B produces cytochrome oxidase. Specimen B does not produce cytochrome oxidase.
1)Specimen A does not produce cytochrome oxidase. 2)Specimen B produces cytochrome oxidase.
Two different bacterial samples, A and B, were inoculated into MR-VP (Methyl Red-Voges Proskauer) broth. The following image shows what the tubes looked like for the Methyl Red portion of the test. http://session.masteringmicrobiology.com/problemAsset/1556545/1/Methyl_red_test_01.jpg Select ALL appropriate statements regarding the pictured specimens that were subjected to the Methyl Red test. Specimen A fermented glucose and formed high levels of acid end-products Specimen A fermented glucose and formed low levels of acid end-products Specimen A can likely convert glucose to lactate, formate, or acetate Specimen B fermented glucose and formed high levels of acid end-products Specimen B is fermented glucose and formed low levels of acid end-products Specimen B can likely convert glucose to lactate, formate, or acetate
1)Specimen A fermented glucose and formed low levels of acid end-products 2)Specimen B fermented glucose and formed high levels of acid end-products 3)Specimen B can likely convert glucose to lactate, formate, or acetate
Two different bacterial samples, A and B, were inoculated onto Eosin Methylene Blue (EMB) agar. What can you conclude based on your observations? http://session.masteringmicrobiology.com/problemAsset/1556535/1/EMB_04.jpg Based on your observation of the pictured specimens that are growing on the EMB agar plate, select ALL appropriate conclusions. Specimen A is able to ferment lactose Specimen A is unable to ferment lactose Specimen A is likely to be Escherichia coli (E. coli) Specimen A is most likely Gram-negative Specimen B is most likely Gram-negative Specimen B is able to ferment lactose Specimen B is unable to ferment lactose Specimen B produces a base during the fermentation of lactose
1)Specimen A is able to ferment lactose 2)Specimen A is likely to be Escherichia coli (E. coli) 3)Specimen A is most likely Gram-negative 4)Specimen B is most likely Gram-negative 5)Specimen B is able to ferment lactose
Two different bacterial samples, A and B, were inoculated into the motility media shown here. http://session.masteringmicrobiology.com/problemAsset/1556544/1/motility_07.jpg Based on your observation of the pictured specimens select ALL appropriate statements. Specimen A is motile Specimen A is nonmotile Specimen B is motile Specimen B is nonmotile
1)Specimen A is nonmotile 2)Specimen B is motile
Two different bacterial samples, A and B, were grown on Gelatin deeps. This is a picture of the test results. http://session.masteringmicrobiology.com/problemAsset/1556563/1/gelatin_hydrolysis_02.jpg Select ALL appropriate statements regarding the pictured Gelatin test results. Specimen A produced gelatinase Specimen A did not produce gelatinase Specimen A hydrolyzed gelatin Specimen B produced gelatinase Specimen B did not produce gelatinase Specimen B hydrolyzed gelatin
1)Specimen A produced gelatinase 2)Specimen A hydrolyzed gelatin 3)Specimen B did not produce gelatinase
Two different bacterial samples, A and B, were analyzed with the Voges-Poskauer (VP) test. The results are pictured here. http://session.masteringmicrobiology.com/problemAsset/1556552/1/Vogues_Proskauer_02.jpg Select ALL appropriate statements regarding the pictured oxidase test results. Specimen A fermented glucose and formed acetoin (acetylmethylcarbinol). Specimen A fermented glucose and formed neutral end-products. Specimen A had a positive result for the VP test. Specimen B fermented glucose and formed acetoin (acetylmethylcarbinol). Specimen B is fermented glucose and formed neutral end-products. Specimen B had a positive result for the VP test.
1)Specimen B fermented glucose and formed acetoin (acetylmethylcarbinol). 2)Specimen B is fermented glucose and formed neutral end-products. 3)Specimen B had a positive result for the VP test.
Observing carbohydrate fermentation A Lactose Fermentation test was performed on two different bacterial samples, A and B. Based on your observations what can you conclude? http://session.masteringmicrobiology.com/problemAsset/1556527/1/carbohydrate_fermentation_test_14.jpg Based on your observation of the pictured Lactose Fermentation tests, choose all appropriate statements. Test organism A ferments lactose Test organism A produced gas Test organism A lowered the pH of the medium Test organism B does not ferment lactose Test organism B produced gas Test organism B lowered the pH of the medium
1)Test organism A ferments lactose 2)Test organism A produced gas 3)Test organism A lowered the pH of the medium 4)Test organism B does not ferment lactose
Use the micrograph of the Gram stain to draw conclusions and make predictions about the indicated bacterium. http://session.masteringmicrobiology.com/problemAsset/1556515/1/mixed_Gram_03.jpg Based on your observation of the indicated bacterium in this Gram stain, select ALL appropriate statements. The bacteria have a staph arrangement. The bacteria pictured are spirochetes. The indicated bacterium is Gram-negative. The indicated bacterium is Gram-positive. Eosin Methylene Blue (EMB) or MacConkey agar would NOT be good choices of media to grow the indicated bacteria. The indicated bacteria produce endotoxin (also known as lipopolysaccharide, LPS). The bacteria pictured are bacilli. The bacteria pictured are cocci.
1)The bacteria have a staph arrangement. 2)The indicated bacterium is Gram-positive. 3)Eosin Methylene Blue (EMB) or MacConkey agar would NOT be good choices of media to grow the indicated bacteria. 4)The bacteria pictured are cocci.
A specimen was inoculated onto the Triple Sugar Iron (TSI) medium pictured here. http://session.masteringmicrobiology.com/problemAsset/1556487/1/TSI_07.jpg Based on your observation of the pictured TSI (Triple Sugar Iron) medium select ALL appropriate conclusions. The bacterium is able to ferment glucose. The pH of the agar decreased following incubation. The bacteria is Gram-positive. The bacterium is unable to ferment lactose and/or sucrose. Hydrogen sulfide (H2S) was produced.
1)The bacterium is able to ferment glucose. 2)The pH of the agar decreased following incubation. 3)The pH of the agar decreased following incubation.
Interpreting biochemical test results (observations versus conclusions) Part A A specimen was inoculated onto the MacConkey agar pictured here. http://session.masteringmicrobiology.com/problemAsset/1556523/1/lactose_fermentation_on_MacConkey.jpg Based on your observation of the pictured MacConkey medium, select ALL appropriate conclusions . (Recall that an observation and a conclusion are different. An observation is simply what you see; conclusions are statements of what you learned from your observations.) The bacteria grew The bacterium is most likely Gram-negative The bacteria ferments lactose The bacterium is unable to ferment sucrose The bacteria is most likely Gram-positive The bacteria has a red/pink pigmentation
1)The bacterium is most likely Gram-negative 2)The bacteria ferments lactose
Interpreting biochemical test results (observations versus conclusions) Part A A specimen was inoculated onto the Triple Sugar Iron (TSI) medium pictured here. http://session.masteringmicrobiology.com/problemAsset/1556491/1/M_luteus_on_TSI_01.jpg Based on your observation of the pictured TSI (Triple Sugar Iron) medium select ALL appropriate conclusions . (Recall that an observation and a conclusion are different. An observation is simply what you see; conclusions are statements of what you determined based on your observations.) There is a black coloration *********** of the tube. The bacterium is unable to ferment glucose. Hydrogen sulfide (H2S) was produced. The bacterium is unable to ferment lactose and/or sucrose. The butt of the medium is red. The slant of the medium is red. The bacteria growing on the slant is yellow. The pH of the agar decreased following incubation.
1)The bacterium is unable to ferment glucose. 2)The bacterium is unable to ferment lactose and/or sucrose.
Use the micrograph of the Gram stain to draw conclusions and make predictions about the indicated bacterium. http://session.masteringmicrobiology.com/problemAsset/1556516/2/1mixed_Gram_01.jpg Based on your observation of the indicated bacterium in this Gram stain, select ALL appropriate statements. The indicated bacterium is a spirochete The indicated bacterium is a bacillus The indicated bacterium has a strepto- formation The indicated bacterium is Gram-positive Eosin Methylene Blue (EMB) or MacConkey agar would NOT be good choices of media to grow the indciated bacterium The indicated bacterium produces endotoxin (also known as lipopolysaccharide, LPS) The indicated bacterium is Gram-negative
1)The indicated bacterium is a bacillus 2)The indicated bacterium has a strepto- formation 3)The indicated bacterium is Gram-positive 4)Eosin Methylene Blue (EMB) or MacConkey agar would NOT be good choices of media to grow the indciated bacterium
Item 3 Flagella arrangement Observe the micrograph and draw conclusions about the indicated bacterium. http://session.masteringmicrobiology.com/problemAsset/1556480/1/Flagella_06.jpg Based on your observation of the indicated bacterium in this micrograph, select ALL appropriate statements. The indicated bacterium has a lophotrichous flagella arrangement. The indicated bacterium is motile. The indicated bacterium has a monotrichous flagella arrangement. The indicated bacterium has a peritrichous flagella arrangement. The indicated bacterium has cilia. The indicated bacterium has an amphitrichous flagella arrangement.
1)The indicated bacterium is motile. 2)The indicated bacterium has a peritrichous flagella arrangement.
Part A Observe the micrograph and draw conclusions about the indicated bacterium. http://session.masteringmicrobiology.com/problemAsset/1556486/1/capsule_04.jpg Based on your observation of the indicated bacterial structure in this micrograph, select ALL appropriate statements. The indicated structure could serve as a virulence factor. The indicated structure is a slime layer. The indicated structure can be used for adhesion. The indicated structure is a capsule. The indicated structure is just a microscopy artifact. The indicated bacterium is resistant to drying (desiccation).
1)The indicated structure could serve as a virulence factor. 2)The indicated structure can be used for adhesion. 3)The indicated structure is a capsule. 4)The indicated bacterium is resistant to drying (desiccation).
A Catalase test was done on an unknown specimen. Observe the pictured result and answer the following question. http://session.masteringmicrobiology.com/problemAsset/1556556/1/catalase_test_03.jpg Select ALL appropriate statements regarding the pictured Catalase test result. The organism can convert hydrogen peroxide to water and oxygen. The organism does not produce catalase. The organism produces catalase. The organism can convert hydrogen peroxide to hydrogen sulfide. The organism is probably a strict anaerobe.
1)The organism can convert hydrogen peroxide to water and oxygen. 2)The organism produces catalase.
An unknown specimen was grown on Mannitol Salt agar (MSA). Observe the pictured result and answer the following question. http://session.masteringmicrobiology.com/problemAsset/1556558/1/MSA_02.jpg Select ALL appropriate statements regarding the pictured Mannitol Salt agar (MSA) test result. The organism tested is most likely Escherichia coli (E. coli). The organism tested is able to grow in the presence of high salt. The organism tested does not ferment mannitol. The organism tested is possibly a type of Staphylococci. The organism tested ferments mannitol.
1)The organism tested is able to grow in the presence of high salt. 2)The organism tested is possibly a type of Staphylococci. 3)The organism tested ferments mannitol.
Analyzing slide of negative stained bacteria Part A What can you conclude about the pictured specimen? http://session.masteringmicrobiology.com/problemAsset/1556521/1/neg_stain_coccus.jpg Based on your observation of this stained specimen, select ALL appropriate statements. The pictured bacteria are cocci This is a picture of a negative stained specimen The bacteria would not have been heat fixed in the preparation of this slide This is a picture of a Gram stained specimen The pictured bacteria are bacilli
1)The pictured bacteria are cocci 2)This is a picture of a negative stained specimen 3)The bacteria would not have been heat fixed in the preparation of this slide
What can you conclude about the Gram stained specimen? http://session.masteringmicrobiology.com/problemAsset/1556517/1/B_pertussis_diplococci_01.jpg Based on your observation of this Gram stained specimen, select ALL appropriate statements. The pictured bacteria are most likely non-acid fast. The pictured bacterium is Gram positive The pictured bacteria are diplococci It can be ruled out that this specimen is taxonomically found in the Staphylococcus genus. The pictured bacteria have strep arrangement The pictured bacteria have a staph arrangement The pictured bacteria produce lipopolysaccharide (LPS), also known as endotoxin.
1)The pictured bacteria are most likely non-acid fast. 2)The pictured bacteria are diplococci 3)It can be ruled out that this specimen is taxonomically found in the Staphylococcus genus. 4)The pictured bacteria produce lipopolysaccharide (LPS), also known as endotoxin.
What can you conclude about the Acid-Fast stained specimen? http://session.masteringmicrobiology.com/problemAsset/1556519/1/mycobacteria_(acid_fast_stain)_01.jpg Based on your observation of this acid-fast stained specimen, select ALL appropriate statements. The pictured bacteria is probably Gram-negative The pictured bacteria have mycolic acid in their cell walls This bacteria probably makes endospores The pictured bacteria are acid-fast The pictured bacteria probably produce lipopolysaccharide (LPS), also known as endotoxin. The pictured bacteria are non-acid-fast The pictured bacteria are possibly a type of mycobacteria
1)The pictured bacteria have mycolic acid in their cell walls 2)The pictured bacteria are acid-fast 3)The pictured bacteria are possibly a type of mycobacteria
Interpreting Gram stain images Part A Use the micrograph of the Gram stain to draw conclusions and make predictions about the pictured bacterium. http://session.masteringmicrobiology.com/problemAsset/1556514/1/gram_neg_cocci.jpg Based on your observation of the Gram stained bacterial specimen, select ALL appropriate statements. The pictured bacteria produce endotoxin (also known as lipopolysaccharide, LPS). The indicated bacterium is Gram-negative. Eosin methylene blue (EMB) or MacConkey agar would NOT be good choices of media to grow the pictured bacteria. The indicated bacterium is Gram-positive. The bacteria pictured are bacilli. The bacteria pictured are spirochetes. The bacteria pictured are cocci.
1)The pictured bacteria produce endotoxin (also known as lipopolysaccharide, LPS). 2)The indicated bacterium is Gram-negative. 3)The bacteria pictured are cocci.
What can you conclude based on your observation of the pictured Sucrose Fermentation test? http://session.masteringmicrobiology.com/problemAsset/1556528/1/carbohydrate_fermentation_test_09.jpg Based on your observation of the pictured Sucrose Fermentation test, choose all appropriate statements. The test organism ferments sucrose The test organism is unable to ferment sucrose The test organism lowered the pH of the medium The test organism raised the pH of the medium The test organism produced gas The test organism did not produce gas
1)The test organism ferments sucrose 2)The test organism lowered the pH of the medium 3)The test organism produced gas
Observe the pictured Sucrose Fermentation test. http://session.masteringmicrobiology.com/problemAsset/1556531/1/carbohydrate_fermentation_test_04.jpg Select the three best hypotheses that could explain why the broth in the Durham tube appears yellow while the rest of the broth appears red. The test organism ferments sucrose best under reduced oxygen conditions. The sample was incubated less than 24 hours, which allowed for only limited fermentation. The media was contaminated. The organism is an obligate aerobe and therefore can only grow inside the Durham tube. The media was prepared wrong. The organism is limited in its ability to ferment sucrose. Since diffusion is restricted within the Durham tube and it contains only a small volume of media, it turned yellow first. The test organism did not ferment sucrose.
1)The test organism ferments sucrose best under reduced oxygen conditions. 2)The sample was incubated less than 24 hours, which allowed for only limited fermentation. 3)The organism is limited in its ability to ferment sucrose. Since diffusion is restricted within the Durham tube and it contains only a small volume of media, it turned yellow first.
An unknown specimen was grown on Indole media. Based on your observation of this specimen choose the appropriate statements. http://session.masteringmicrobiology.com/problemAsset/1556561/1/Indole_negative_01.jpg Select ALL appropriate statements regarding the pictured Indole test. This is a picture of a negative test result. This is a picture of a positive test result. This test is a part of the IMViC panel of tests The organism tested fermented indole. The organism tested converts tryptophan to indole. This media is inoculated by stabbing the agar in the tube.
1)This is a picture of a negative test result. 2)This test is a part of the IMViC panel of tests 3)This media is inoculated by stabbing the agar in the tube.
Below is a Glucose Fermentation test. http://session.masteringmicrobiology.com/problemAsset/1556530/1/carbohydrate_fermentation_test_08.jpg Choose all appropriate statements about the Glucose Fermentation test. This test detects a fermentation reaction This media is inoculated using an inoculating loop The test contains phenol red which turns yellow under acidic conditions This media is inoculated with a mixed culture The mouth of the tube should be flamed prior to inoculation and immediately before capping the tube This is a selective media This test gives information about Gram property
1)This test detects a fermentation reaction 2)This media is inoculated using an inoculating loop 3)The test contains phenol red which turns yellow under acidic conditions 4)The mouth of the tube should be flamed prior to inoculation and immediately before capping the tube
A student is testing a milk sample, and carries out the dilution scheme in the diagram below. What is the total dilution of Tube C? 10-1 10-4 10-3 10-5
10-4
Imagine you and a partner are preparing a serial dilution of a sample of pond water. While you were watching your agar, your partner labeled several test tubes with the numbers below. Which of these numbers correctly expresses a dilution? Imagine you and a partner are preparing a serial dilution of a sample of pond water. While you were watching your agar, your partner labeled several test tubes with the numbers below. Which of these numbers correctly expresses a dilution? 104 5.2 X 104 cfu/ml 5.2 X 10-4cfu/g 10-4
10-4
What is the total dilution of tube 5 in this serial dilution scheme? 10-6 105 10-1 103 10-3 10-4 10-5
10-5
A food microbiologist is testing ground meat to estimate the bacterial concentration. He carries out the following serial dilution scheme. What is the total dilution of Plate D's sample? 10-7 10-1 10-6 10-4
10-6
Which of the following bacterial concentrations would produce a TFTC plate at the 10-4 dilution? 2 × 106 organisms/ml 2 × 105 organisms/ml 2 × 108 organisms/ml 2 × 107 organisms/ml
2 × 105 organisms/ml
A food microbiologist carried out a serial dilution procedure using a 1-gram sample of ground meat. After incubation, the plates had the results shown in this photograph. What was the bacterial concentration of the original sample of ground meat? 8.0 X 107 cfu/g 5.8 X 107 cfu/g 5.8 X 10-7 cfu/g 10-6
5.8 X 107 cfu/g
You found 67 colonies on the ground beef plate with the 10-2 dilution. What is the concentration of bacteria per milliliter of beef? 6.7 × 103 CFU/ml 6.7 × 104 CFU/ml 6.7 × 102 CFU/ml 67
6.7 × 103 CFU/ml
If you had fresh lettuce containing 9.3 × 103 organisms/ml, how many colonies would you expect to see on a plate that represents a 10-2 dilution? 93 930 9300 9
93
The organism tested is protected against oxygen radicals. The image shows a positive test result. The organism tested is probably an aerobe or a facultative anaerobe.
A Catalase test was done on an unknown specimen. Observe the pictured result and answer the following question. Select ALL appropriate statements regarding the pictured Catalase test result.
After running this experiment, you find that the carrots you tested had only 15 bacteria/ml. Your lab partner states that this number is so low that the carrots do not need further treatment. Why should you disagree? None of the available answers are correct. Since these organisms are Gram negative, they are definitely pathogenic, so even a small dose could cause disease. A low number of organisms does not indicate the absence of pathogens. The 15 bacteria are resistant to the erythromycin, methicillin, and bacitracin found in EMB agar.
A low number of organisms does not indicate the absence of pathogens.
Which of the following would produce a countable plate? A solution containing 1.9 × 104 at a 10-2 dilution A solution containing 1.6 × 107 at a 10-6 dilution A solution containing 2.1 × 104 at a 10-1 dilution A solution containing 2.5 × 107 at a 10-2 dilution
A solution containing 1.9 × 104 at a 10-2 dilution
Litmus
As oxidation reactions occur during the process of fermentation, which litmus milk substrate acts as an electron acceptor (getting reduced in the process)?
Part G You observe colonies growing on EMB agar that are blue-black with a metallic green sheen. What species of bacteria is this likely to be?
E.coli
Part F You inoculate an organism onto blood agar and observe a clear zone surrounding the bacterial growth. What type of hemolysis is indicated by this observation?
Beta hemolysis
Part E Which of the following describes an INCORRECT association regarding hemolytic activity?
Beta hemolysis; results in a greenish halo around the bacterial growth
Which of the following best describes serial dilution? Which of the following best describes serial dilution? Inoculum from one dilution is transferred to a sequence of plates. Each tube in a set of tubes is a dilution of the previous tube. Identical volumes of a bacterial sample are transferred to several Petri dishes. Melted agar is poured into a series of sterile Petri plates.
Each tube in a set of tubes is a dilution of the previous tube.
What is the indicator bacteria for contamination in water?
E. coli
What are two coliform bacterium are found in fecal contamination?
E. coli and E. aerogenes
If a bacterium can ferment one type of sugar, it can ferment any sugar.
False
Sulfanilic acid and a-naphthylamine are red reagents that become clear in the presence of nitrite.
False (it will appear red in the presence of nitrite)
Simmons citrate slants require the addition of a reagent to see results of citrate utilization.
False - If bacteria use citrate, they will turn the agar from green to blue due to a rise in alkalinity; no reagents will be required.
Part B What is the purpose of adding salt to mannitol salt agar?
High concentrations of salt inhibit the growth of non-halophilic organisms but allow for the growth of bacteria from the genus Staphylococci.
Kelsey did not address the motility of the organism As evidenced by the lack of an aqueous layer on the top of the medium, Kelsey forgot to add Kovacs' reagent. As such, she could not truly make a conclusion about whether or not indole was produced
Kelsey inoculated her unknown bacterial sample onto SIM agar and obtained the pictured result. She described her sample as indole negative and hydrogen sulfide (H2S) positive. Unfortunately, Kelsey lost points for her description of her SIM test results. Curious by nature, she turned to you to ask if you could help her determine why she did not earn full credit for her work. Based on your observation of Kelsey's SIM test, select the reason(s) she lost points.
Describe the confirmation test. What do these inhibit?
Levine EMB or Endo agar is inoculated with positive broth culture; gram + bacteria
A student is learning how to perform serial dilutions, using a stock solution of E. coli. He was instructed to use the dilution scheme shown in the diagram. The stock solution was turbid, as shown below. He delivered 1 ml from each tube into a separate sterile Petri dish and poured melted agar into each dish. When he examined the plates after 48 hour incubation at 37oC, he found no growth in any of the seven plates. What could explain these results? The same pipette was used throughout the experiment. He did not use aseptic technique. The agar was not at the correct temperature when poured. He did not stack the plates while cooling.
The agar was not at the correct temperature when poured.
Part C You observe red colored colonies growing on MacConkey agar. What does this indicate about the organism?
The organism is able to ferment lactose.
Item 1: Part A You observe a yellow zone surrounding growth on mannitol salt agar. What does this indicate about the organism?
The organism is able to ferment mannitol.
Why are the coliform plates incubated at 37° C? None of the available answers is correct. Coliforms, by definition, are thermophiles. They grow best at body temperature. The nutrients will not be released from EMB agar at temperatures below approximately 35° C.
They grow best at body temperature.
Characteristics of bacterial colonies are not enough for identification of an unknown.
True
The selective nature of the MacConkey agar is due to the presence of crystal violet, which inhibits gram-positive bacterial growth.
True
You should always perform the Gram stain first when attempting to identify a bacterial unknown
True- Gram stain will aid in determining which tests to perform in your identification.
Urease is a hydrolytic enzyme that attacks the nitrogen and carbon bond in urea.
What is the function of the enzyme urease?
E.aerogenes; rose color change after the addition of Barritt's reagents.
Which of the following associations is correct regarding the Voges-Proskauer test?
Gram-negative, non-spore-forming, bacilli
Which of the following correctly describes the cellular morphology for members of the Enterobacteriaceae family?
