Fitness of Antibiotic-Resistant Bacteria in the Environment: A Laboratory Activity †
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Authors:
Massimiliano Marvasi1,*,
Manika Choudhury1,
Nimisha Binesh Vala1,
Max Teplitski2
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Received 21 October 2016 Accepted 28 January 2017 Published 21 April 2017
- ©2017 Author(s). Published by the American Society for Microbiology.
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[open-access] This is an Open Access article distributed under the terms of the Creative Commons Attribution-Noncommercial-NoDerivatives 4.0 International license (https://creativecommons.org/licenses/by-nc-nd/4.0/ and https://creativecommons.org/licenses/by-nc-nd/4.0/legalcode), which grants the public the nonexclusive right to copy, distribute, or display the published work.
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†Supplemental materials available at http://asmscience.org/jmbe
- *Corresponding author. Mailing address: Department of Natural Sciences, School of Science and Technology, Middlesex University, The Burroughs, London NW4 4BT, UK. Phone: 0044 208 411 4902. E-mail: [email protected].
Abstract:
In this laboratory experiment, we propose an opportunity for students to broaden their understanding of the ecology of antibiotic-resistant and sensitive waterborne bacteria. Antibiotics can be found in rivers or soil as a consequence of agricultural practices or as a result of human use. Concentrations of antibiotics in the environment may range from a few ng to μg L−1. Such concentrations can affect the selection and fitness of resistant bacteria. In this laboratory activity, students learn how to set up a fitness experiment by using an isogenic pair of antibiotic-resistant and sensitive bacteria in the presence or absence of selective pressure. Microcosms were generated by using filtered river water containing populations of resistant and sensitive bacteria. Competition of both populations was measured in the presence or absence of antibiotics. Students appreciated the use of microcosms for in vitro experiments and the extent to which the fitness of resistant and sensitive bacteria changed in the presence and/or absence of a selective pressure in river water. Student learning was measured by using different types of assessments: multiple-choice, true/false, fill in the blanks, laboratory skills observations, and laboratory reports. After the laboratory activity, the percentage of correct answers significantly rose from ~20% to ~85%. Laboratory skills were also evaluated during the exercises, showing no major issues during the experiment. Students showed proficiency in analyzing the complexity of fitness data by reaching a mean of 5.57 (standard error 0.57) over a maximum score of 7 points.
References & Citations
Supplemental Material
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Appendix 1: Material for the instructor (procedures for media preparation, inoculation of the strain, collection of river water, consumables and equipment required) — Appendix 2: Student laboratory handout and answer key — Appendix 3: Reporting card and example of results — Appendix 4: Pre- and post-activity assessment and answer key to assess LO 1 — Appendix 5: Rubrics used to assess LO 2 and LO 3
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Abstract:
In this laboratory experiment, we propose an opportunity for students to broaden their understanding of the ecology of antibiotic-resistant and sensitive waterborne bacteria. Antibiotics can be found in rivers or soil as a consequence of agricultural practices or as a result of human use. Concentrations of antibiotics in the environment may range from a few ng to μg L−1. Such concentrations can affect the selection and fitness of resistant bacteria. In this laboratory activity, students learn how to set up a fitness experiment by using an isogenic pair of antibiotic-resistant and sensitive bacteria in the presence or absence of selective pressure. Microcosms were generated by using filtered river water containing populations of resistant and sensitive bacteria. Competition of both populations was measured in the presence or absence of antibiotics. Students appreciated the use of microcosms for in vitro experiments and the extent to which the fitness of resistant and sensitive bacteria changed in the presence and/or absence of a selective pressure in river water. Student learning was measured by using different types of assessments: multiple-choice, true/false, fill in the blanks, laboratory skills observations, and laboratory reports. After the laboratory activity, the percentage of correct answers significantly rose from ~20% to ~85%. Laboratory skills were also evaluated during the exercises, showing no major issues during the experiment. Students showed proficiency in analyzing the complexity of fitness data by reaching a mean of 5.57 (standard error 0.57) over a maximum score of 7 points.

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Author and Article Information
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Received 21 October 2016 Accepted 28 January 2017 Published 21 April 2017
- ©2017 Author(s). Published by the American Society for Microbiology.
-
[open-access] This is an Open Access article distributed under the terms of the Creative Commons Attribution-Noncommercial-NoDerivatives 4.0 International license (https://creativecommons.org/licenses/by-nc-nd/4.0/ and https://creativecommons.org/licenses/by-nc-nd/4.0/legalcode), which grants the public the nonexclusive right to copy, distribute, or display the published work.
-
†Supplemental materials available at http://asmscience.org/jmbe
- *Corresponding author. Mailing address: Department of Natural Sciences, School of Science and Technology, Middlesex University, The Burroughs, London NW4 4BT, UK. Phone: 0044 208 411 4902. E-mail: [email protected].
Figures
Main findings reported after the three-week laboratory experiment. Box plots represent the fitness of resistant and sensitive bacteria under different concentrations of tetracycline. On the y axis, negative value represents sensitive bacteria that are out-competing the resistant bacteria. Positive values represent resistant bacteria outcompeting the sensitive cells. When the ratio is equal the competition index is 0. (A) the fitness of resistant and sensitive bacteria at day 0 and day 2 in the absence of tetracycline. Microcosms were prepared using Thames River water in which the microbial community was removed via filtration. (B) In the presence of tetracycline (selective pressure), resistant bacteria have an increased fitness. Boxes include the lower and upper quartiles, lines within the box are the medians and whiskers indicate the degree of dispersion of the data.

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FIGURE 2
Main findings reported after the three-week laboratory experiment. Box plots represent the fitness of resistant and sensitive bacteria under different concentrations of tetracycline. On the y axis, negative value represents sensitive bacteria that are out-competing the resistant bacteria. Positive values represent resistant bacteria outcompeting the sensitive cells. When the ratio is equal the competition index is 0. (A) the fitness of resistant and sensitive bacteria at day 0 and day 2 in the absence of tetracycline. Microcosms were prepared using Thames River water in which the microbial community was removed via filtration. (B) In the presence of tetracycline (selective pressure), resistant bacteria have an increased fitness. Boxes include the lower and upper quartiles, lines within the box are the medians and whiskers indicate the degree of dispersion of the data.
Example of workflow of the experiments conducted over the three-week period. PBS = phosphate-buffered saline.

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FIGURE 1
Example of workflow of the experiments conducted over the three-week period. PBS = phosphate-buffered saline.
Pre-post test assessment LO 1. Percentages of correct answers are shown. The percentage of correct answers was significantly different in all the tests (t-test p=0.05). Error bars represent standard error. Please refer to Appendix 4 for the typology of questions.

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FIGURE 3
Pre-post test assessment LO 1. Percentages of correct answers are shown. The percentage of correct answers was significantly different in all the tests (t-test p=0.05). Error bars represent standard error. Please refer to Appendix 4 for the typology of questions.
Assessment of student performance (LO 2). The scale ranges from very good (5 pts.) to poor (1 pt.). Tasks assigned: A = The student is able to identify contamination on the plates. B = The student can properly patch colonies. C = The student can choose when to use selective plates and non-selective plates. D = The student is able to record the results in the reporting card. E = The student is able to pipette properly.

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FIGURE 4
Assessment of student performance (LO 2). The scale ranges from very good (5 pts.) to poor (1 pt.). Tasks assigned: A = The student is able to identify contamination on the plates. B = The student can properly patch colonies. C = The student can choose when to use selective plates and non-selective plates. D = The student is able to record the results in the reporting card. E = The student is able to pipette properly.