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Learn Microbiology Skills and Concepts with Laboratory Experiments in Microbiology 10th Edition


Laboratory Experiments in Microbiology 10th Edition Answer Key


If you are taking a microbiology course or preparing for a career in microbiology, you need a reliable and comprehensive textbook that covers all the essential concepts and skills. One such textbook is Laboratory Experiments in Microbiology 10th Edition by Ted R. Johnson and Christine L. Case.




laboratory experiments in microbiology 10th edition answer key


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This textbook provides engaging labs with instruction on performing basic microbiology techniques and applications for undergraduate students in diverse areas, including the biological sciences, allied health sciences, agriculture, environmental science, nutrition, pharmacy, and various pre-professional programs.


In this article, we will give you an overview of this textbook and its answer key. We will also provide you with some sample answers for selected exercises to help you check your understanding and improve your performance.


Introduction




Laboratory Experiments in Microbiology 10th Edition is a spiral-bound manual that contains 57 thoroughly class-tested and easily customizable exercises. It was published by Pearson Education in 2012 and has 496 pages.


The authors of this textbook are Ted R. Johnson and Christine L. Case, both experienced professors of microbiology at different colleges in the United States. They have also written other popular microbiology textbooks, such as Microbiology: An Introduction and Brock Biology of Microorganisms.


Some of the main features and benefits of this textbook are:



  • It has an updated art program and a full-color design, integrating valuable micrographs throughout each exercise.



  • It has enhanced laboratory reports for each exercise with new clinical applications questions, as well as questions relating to hypotheses or expected results.



  • It has refined experiments throughout the manual and an extensively revised exercise on transformation in bacteria using pGLO to introduce students to this important technique.



  • It has a companion website that offers additional resources for students and instructors, such as quizzes, flashcards, videos, animations, case studies, and more.



How to Use the Answer Key




The answer key for Laboratory Experiments in Microbiology 10th Edition is not included in the textbook itself. Instead, it is available online on the Pearson website for instructors who have adopted this textbook for their courses. To access the answer key, you need to register as an instructor and request access from Pearson.


Once you have access to the answer key, you can use it to check your answers for each exercise and learn from your feedback. The answer key provides detailed explanations and references for each question, as well as tips and suggestions for improving your skills and understanding.


However, you should not rely solely on the answer key to study for your exams or assignments. The answer key is meant to be a supplementary tool, not a substitute for your own work and effort. You should use the answer key as a guide, not as a crutch. Here are some tips on how to use the answer key effectively:



  • Do the exercises first before looking at the answer key. Try to solve the problems and answer the questions on your own, using your textbook, notes, and other resources as needed.



  • Compare your answers with the answer key and identify any errors or gaps in your knowledge. Review the explanations and references provided by the answer key and try to understand why your answers were wrong or incomplete.



  • Correct your mistakes and revise your answers accordingly. Make sure you can explain your reasoning and logic behind your answers.



  • Use the answer key as a study tool to reinforce your learning and retention. Review the answer key periodically and test yourself on the concepts and skills covered by each exercise.



Sample Answers for Selected Exercises




To give you an idea of what the answer key looks like and how it can help you, we will provide you with some sample answers for selected exercises from Laboratory Experiments in Microbiology 10th Edition. These are not the complete answers, but only excerpts to illustrate the format and content of the answer key. For the full answers, you need to access the online answer key from Pearson.


Exercise 1: Aseptic Technique and Streak Plate Method




This exercise introduces you to the basic techniques of working with microorganisms in the laboratory, such as aseptic technique, inoculation, incubation, isolation, and identification. You will learn how to transfer microbial cultures from one medium to another without contamination, and how to obtain pure cultures of bacteria by using the streak plate method.


Here are some sample questions and answers from this exercise:



  • What is aseptic technique? Why is it important in microbiology?



  • Aseptic technique is a set of procedures and practices that prevent contamination of microbial cultures, media, equipment, or personnel by unwanted microorganisms. It is important in microbiology because it ensures the accuracy and validity of experimental results, as well as the safety and health of laboratory workers and the environment.



  • What are some examples of aseptic technique?



  • Some examples of aseptic technique are: flaming the loop or needle before and after each transfer; flaming the mouth of tubes or bottles before and after opening or closing them; holding tubes or bottles at an angle to minimize exposure to air; using sterile pipettes, swabs, or forceps for transferring liquids or solids; wearing gloves, lab coats, goggles, and masks when handling potentially infectious materials; disinfecting the work area before and after each experiment; disposing of contaminated materials properly.



  • What is the purpose of streaking a plate?



  • The purpose of streaking a plate is to obtain isolated colonies of bacteria from a mixed culture. An isolated colony is a group of bacteria that originated from a single cell and grew into a visible mass on the surface of the agar. By obtaining isolated colonies, one can identify and study the characteristics of individual bacterial species in a mixed culture.



  • What are some factors that affect the quality of streaking a plate?



  • Some factors that affect the quality of streaking a plate are: the amount and distribution of inoculum on the loop or needle; the angle, speed, and pressure of streaking; the number and direction of streaks; the size and shape of the plate; the type and consistency of the agar; the incubation time and temperature.



Exercise 10: Enumeration of Bacteria: Standard Plate Count




This exercise teaches you how to estimate the number of viable bacteria in a liquid sample by using the standard plate count method. You will learn how to prepare serial dilutions of a bacterial culture, how to plate out known volumes of diluted samples on agar plates, how to count colonies on plates that have between 30 and 300 colonies (the countable range), and how to calculate the original concentration of bacteria in the sample.


Here are some sample questions and answers from this exercise:



  • What is a serial dilution? How is it performed?



  • A serial dilution is a stepwise dilution of a liquid sample by using a constant dilution factor. It is performed by transferring a known volume of sample into a known volume of sterile diluent (such as water or saline), mixing well, and repeating this process with subsequent tubes until reaching the desired dilution. For example, to make a 10-fold serial dilution of a sample, one would transfer 1 mL of sample into 9 mL of diluent, mix well, and then transfer 1 mL of this diluted sample into another 9 mL of diluent, and so on.



  • What is the difference between a viable count and a total count?



  • A viable count is a measure of the number of living cells in a sample, while a total count is a measure of the number of all cells (living and dead) in a sample. A viable count is usually obtained by plating out a sample on an agar medium and counting the colonies that grow after incubation. A total count is usually obtained by using a microscope and a counting chamber to count the cells in a known volume of sample.



  • How do you calculate the original concentration of bacteria in a sample from the standard plate count method?



  • To calculate the original concentration of bacteria in a sample from the standard plate count method, one needs to know the number of colonies on a plate that falls within the countable range (30-300 colonies), the volume of diluted sample that was plated out, and the dilution factor of that sample. The formula for calculating the original concentration is:



  • Original concentration (CFU/mL) = Number of colonies x Dilution factor / Volume plated



  • For example, if one plated 0.1 mL of a sample that was diluted 10^-6 times and obtained 120 colonies on the plate, then the original concentration would be:



  • Original concentration (CFU/mL) = 120 x 10^6 / 0.1 = 1.2 x 10^9 CFU/mL



Exercise 21: Identification of an Unknown Bacterium Using a Series of Biochemical Tests




This exercise challenges you to apply your knowledge and skills of microbiology to identify an unknown bacterium using a series of biochemical tests. You will receive a pure culture of an unknown bacterium and perform various tests to determine its characteristics, such as Gram reaction, shape, motility, oxygen requirements, carbohydrate fermentation, enzyme production, and more. You will then compare your results with a dichotomous key or a table of bacterial characteristics to identify your unknown bacterium.


Here are some sample questions and answers from this exercise:



  • What is a dichotomous key? How is it used for bacterial identification?



  • A dichotomous key is a tool that helps identify an organism by using a series of paired statements or questions that describe its features or characteristics. Each pair of statements or questions leads to another pair until the organism is identified or eliminated. For bacterial identification, a dichotomous key can be based on various criteria, such as Gram reaction, shape, arrangement, motility, oxygen requirements, biochemical reactions, etc.



  • What are some examples of biochemical tests for bacterial identification?



  • Some examples of biochemical tests for bacterial identification are: catalase test, oxidase test, indole test, methyl red test, Voges-Proskauer test, citrate utilization test, urease test, phenylalanine deaminase test, gelatin hydrolysis test, starch hydrolysis test, casein hydrolysis test, lipid hydrolysis test, nitrate reduction test, hydrogen sulfide production test, etc.



  • How do you interpret the results of biochemical tests?



  • The results of biochemical tests are usually interpreted by observing the color change or the presence or absence of gas bubbles or precipitates in the medium or reagent after incubation. The color change or other indicators are due to the production or consumption of certain substances by the bacteria as they metabolize the substrate in the medium or reagent. For example, in the indole test, if bacteria produce indole from tryptophan in tryptone broth, then adding Kovac's reagent will result in a red color in the upper layer. In contrast, if bacteria do not produce indole from tryptophan in tryptone broth then adding Kovac's reagent will result in no color change or a yellow color in the upper layer.



  • How do you record and report the results of biochemical tests?



  • The results of biochemical tests are usually recorded and reported by using symbols, abbreviations, or words that indicate whether the test was positive or negative, or what type of reaction occurred. For example, in the catalase test, a positive result is indicated by a + sign or the word "positive", while a negative result is indicated by a - sign or the word "negative". Alternatively, some tests may use letters or numbers to indicate different types of reactions. For example, in the sugar fermentation test, an A (acid) indicates that acid was produced from the sugar, a G (gas) indicates that gas was produced from the sugar, and a K (alkaline) indicates that no acid or gas was produced from the sugar.



Exercise 35: Antimicrobial Susceptibility Testing: The Kirby-Bauer Method




This exercise demonstrates how to determine the susceptibility or resistance of bacteria to different antimicrobial agents by using the Kirby-Bauer method. You will learn how to prepare a lawn of bacteria on an agar plate, how to apply antibiotic-impregnated disks on the surface of the agar, how to incubate the plate and observe the zones of inhibition around the disks, and how to interpret and report the results by using standard tables of interpretive criteria.


Here are some sample questions and answers from this exercise:



  • What is the Kirby-Bauer method? How does it work?



  • The Kirby-Bauer method is a standardized disk diffusion method for antimicrobial susceptibility testing. It works by measuring the diameter of the zone of inhibition around an antibiotic-impregnated disk on an agar plate inoculated with a standardized concentration of bacteria. The zone of inhibition is the area where bacterial growth is prevented or reduced by the antibiotic. The diameter of the zone of inhibition reflects the sensitivity of the bacteria to the antibiotic and can be compared with standard tables of interpretive criteria to determine whether the bacteria are susceptible, intermediate, or resistant to the antibiotic.



  • What are some factors that affect the accuracy and reliability of the Kirby-Bauer method?



  • Some factors that affect the accuracy and reliability of the Kirby-Bauer method are: the quality and concentration of the antibiotic disks; the type and thickness of the agar medium; the inoculum size and distribution of bacteria on the agar plate; the incubation time and temperature; the measurement technique and reading errors.



  • How do you measure and record the zones of inhibition?



  • To measure and record the zones of inhibition, one needs to use a ruler or a caliper and measure the diameter of each zone in millimeters (mm), including both edges of the zone. The measurement should be done on the underside of the plate without removing the lid. The measurement should be recorded by writing down the name or code of each antibiotic disk and its corresponding zone diameter. For example: PEN 25 mm; ERY 18 mm; TET 12 mm.



  • How do you interpret and report the results of antimicrobial susceptibility testing?



  • To interpret and report the results of antimicrobial susceptibility testing, one needs to use standard tables of interpretive criteria that are based on the type of bacteria, the type of antibiotic, and the diameter of the zone of inhibition. The tables provide the breakpoints for each category of susceptibility or resistance. For example, for Escherichia coli tested against ampicillin, a zone diameter of 29 mm or more indicates susceptibility, a zone diameter of 14 mm or less indicates resistance, and a zone diameter of 15-28 mm indicates intermediate susceptibility. The results of antimicrobial susceptibility testing are usually reported by using symbols, abbreviations, or words that indicate the category of susceptibility or resistance. For example, S for susceptible, I for intermediate, and R for resistant.



Exercise 50: Immunology: Agglutination Reactions and Blood Typing




This exercise introduces you to the principles and applications of immunology, the study of the immune system and its responses to foreign substances. You will learn how to perform agglutination reactions, which are tests that involve the clumping of antigens and antibodies. You will also learn how to determine your blood type by using agglutination reactions with anti-A and anti-B sera.


Here are some sample questions and answers from this exercise:



  • What is an antigen? What is an antibody?



  • An antigen is a substance that can trigger an immune response in the body. An antigen can be a foreign molecule, such as a protein, polysaccharide, lipid, or nucleic acid, that is recognized as non-self by the immune system. An antibody is a protein produced by specialized white blood cells called B lymphocytes (or B cells) in response to an antigen. An antibody can bind specifically to an antigen and neutralize it or mark it for destruction by other immune cells.



  • What is an agglutination reaction? How does it work?



  • An agglutination reaction is a test that involves the clumping of antigens and antibodies. It works by mixing a known antigen (such as red blood cells) with a known antibody (such as anti-A serum) and observing whether or not agglutination occurs. Agglutination occurs when the antibody binds to multiple antigens on different cells and forms cross-links that cause the cells to stick together. Agglutination indicates a positive reaction and means that the antigen and antibody are compatible. No agglutination indicates a negative reaction and means that the antigen and antibody are not compatible.



  • What is blood typing? How is it done?



  • Blood typing is a method to determine a person's blood type based on the presence or absence of certain antigens on the surface of red blood cells. Blood typing is done by using agglutination reactions with anti-A and anti-B sera. A drop of blood is mixed with each serum separately on a slide or a card and observed for agglutination. If agglutination occurs with anti-A serum, it means that the blood has A antigens and is type A. If agglutination occurs with anti-B serum, it means that the blood has B antigens and is type B. If agglutination occurs with both sera, it means that the blood has both A and B antigens and is type AB. If no agglutination occurs with either serum it means that the blood has neither A nor B antigens and is type O.



  • What is the Rh factor? How is it determined?



  • The Rh factor is another type of antigen on the surface of red blood cells. It is named after the rhesus monkey, where it was first discovered. The Rh factor can be either positive or negative, depending on whether or not the antigen is present. The Rh factor is determined by using agglutination reactions with anti-Rh serum. A drop of blood is mixed with anti-Rh serum on a slide or a card and observed for agglutination. If agglutination occurs, it means that the blood has the Rh antigen and is Rh-positive. If no agglutination occurs, it means that the blood does not have the Rh antigen and is Rh-negative.



  • Why is blood typing important? What are some applications of blood typing?



  • Blood typing is important for transfusion compatibility and pregnancy care. Blood typing can help prevent transfusion reactions, which are serious and potentially life-threatening complications that occur when incompatible blood types are mixed together. Blood typing can also help prevent hemolytic disease of the newborn (HDN), which is a condition that occurs when an Rh-negative mother carries an Rh-positive fetus and develops antibodies against the fetal red blood cells. Blood typing can also be used for forensic purposes, such as identifying suspects or victims of crimes, accidents, or disasters.



Conclusion




In this article, we have given you an overview of Laboratory Experiments in Microbiology 10th Edition and its answer key. We have also provided you with some sample answers for selected exercises to


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