Laboratory Experiments in Microbiology (11th Edition)
11th Edition
ISBN: 9780321994936
Author: Ted R. Johnson, Christine L. Case
Publisher: PEARSON
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Chapter 22, Problem 4CT
A biological indicator used in autoclaving is a vial containing
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A pure culture was inoculated onto a Mueller-Hinton agar plate. The Kirby-Bauer procedure was performed. One of the drugs tested showed a large zone of inhibition but also had small colonies growing within this zone. Further testing showed that these colonies were not the results of contamination. Why would these colonies be present within this zone of inhibition?
A new chemical disinfectant was tested for activity against Staphylococcus growth. The bacteria were incubated in bacterial growth medium + disinfectant for 24 hours, then one loopful of the mixture was transferred to fresh medium without the disinfectant (subculturing) and incubating the subculture. The initial culture and subcultures were evaluated for growth after incubation. (+ = growth; - = no growth)
Dilution
Initial
Subculture
1:2
-
-
1:4
-
-
1:8
-
+
1:16
+
+
1:32
+
+
Based on these results, which of the following statements is true regarding the effectiveness of this disinfectant against this bacterium?
The disinfectant is bacteriostatic at 1:4 dilution.
The disinfectant is bacteriostatic at 1:2 dilution.
The disinfectant is NOT bacteriostatic at any of the dilutions tested.
The disinfectant is bacteriostatic at 1:8 dilution.
The disinfectant is bacteriostatic at 1:16 dilution.
Answer the following questions briefly and concisely
1.How do bacteria in a chemostat and those in a batch culture vary from one another? 2. What happens in a chemostat if the dilution rate is higher than the organism's maximum specific growth rate? 3.Does a chemostat require the use of pure cultures? 4. Why would a complicated culture media for Leuconostoc mesenteroides be simpler to make than one with a fixed chemical composition?
Chapter 22 Solutions
Laboratory Experiments in Microbiology (11th Edition)
Ch. 22 - Prob. 1QCh. 22 - Prob. 2QCh. 22 - Give an example of a nonlaboratory use of each of...Ch. 22 - Define the term pasteurization. What is the...Ch. 22 - Explain why fungi and Bacillus sometimes grow...Ch. 22 - Assume that a DRT value for autoclaving a culture...Ch. 22 - Indicators are used in autoclaving to ensure that...Ch. 22 - A biological indicator used in autoclaving is a...Ch. 22 - The source of Legionella causing...
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- Contrast the terms thermal death time and decimalreduction time. How would the presence of bacterialendospores affect either value? What time and temperature is necessary to ensure sterility in the autoclave?arrow_forwardBelow are morphological, physiological and biochemical characteristics of an unknown luminous bacterium isolated from the gills of a marine fish. Use the data below to identify the isolate. Make an identification scheme Test Unknown Isolate B 1 Luminescence Positive 2 Cell Shape Straight Rods 3 Gram Staining Negative 4 Oxygen Requirement Facultative Anaerobe 5 Motility (Hanging Drop) Motile 6 Growth at 0% NaCl Negative 7 3% NaCl Positive 8 6 % NaCl Positive 9 Accumulation of PHB Positive 10 Flagella 1 Polar 11 Oxidase Positive 12 Nitrate Reduction 13 Gelatinase Negative 14 Growth at 35OC Positive 15 Growth at 4OC Negative 16 Methyl Red Positive 17 Voges-Proskauer Positive 18 Catalase Positive 19 Starch Hydrolysis Negative 20 Lysine…arrow_forwardExplain why the media where the Staphylococcus aureus is plated has turned yellow but the media where Staphyloccocus epidermidis plated is still pink? The media used would be the Mannitol Salt Agar Medium.arrow_forward
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- Describe characteristics of Streptococcus Agalactiae in the Agar: (How does colonies look like (color) and explain does it grow on that agar. (Don't have to write the incubation period) ~ Only describe how would it look like on the Agar: Blood Agar (Aerobic) MacConkey EMB PEA Mannitol Salt Agar Chocolate Agar Nutrient Agararrow_forwardCan you please discuss the principles of using Motility Test Medium for the detection of bacterial motility. Focus on the components of the medium and the purpose of each component. Note: You may refer to different culture media manuals like Difco, BBL, etc.arrow_forwardThere are two cultures of yeast cells in the pictures, one has been incubated for 6 hours and one has been incubated for 24 hours. After a 10x dilution by taking 100µl of each culture and adding it to 900 µl water in a microcentrifuge tube and 100µl sample from the tube was taken to view in the counting chamber. a) Count the total number of yeast cells for each culture respectively b) Calculate the concentration and density of yeast cells for each culture respectivelyarrow_forward
- You are transferring a bacterial culture from a tube of broth to a Petri dish containing trypticase soy agar. Please list the steps that are necessary to make the transfer successfully and with minimal risk. of contamination.arrow_forwardAccording to the table above, name 1 method that is least effective in killing endospores and explain why.arrow_forwardArcanobacterium haemolyticum may cause pharyngitis or cutaneous infections. It grows as a tiny colony that is beta hemolytic. Dark pits in the agar may be seen when removing the colonies. The organism is catalase negative, and may be differentiated from A. pyogenes by what test? Indicate the reactions for each.arrow_forward
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