A HANDFUL OF BACTERIA : A SIMPLE ACTIVITY THAT ENGAGES STUDENTS TO THINK AND WRITE LIKE A SCIENTIST

Non-major students taking science courses to fulfll degree requirements may show low interest in traditonal lecture-based classrooms. While professors may try to incorporate hands-on actvites to the classroom to foster enthusiasm, the development of a low-cost, low-hazard scientfc actvity that engages students can be challenging. Moreover, teaching and evaluatng critcal thinking, scientfc literacy, quanttatve analysis and writng skills utlizing such actvites require asking carefully designed questons. Here, I introduce a tested efectve, inexpensive, 20-minute in-classroom microbiology deep-learning actvity, and explain how it can be adapted to other disciplines of science. From one simple exercise, students conducted literature research, performed statstcal analysis and made quanttatve/causatve conclusions. Students also learned to write, appreciate and critcally analyze a scientfc paper.


INTRODUCTION
Scientfc inquiry or similar science courses are ofen required for non-science majors by higher educaton insttutons.As with other core curricula, students may show a lack of motvaton due to the false impression that it is irrelevant to their careers and that it is frustratngly difcult (Glynn, Taasoobshirazi & Brickman, 2009).Consequently, the learning outcome is generally poor.Previous studies suggested that students' engagement to an instructonal episode is primarily based on the form of actvity, and that "hands-on" actvites with technology involvement elicit higher interest (Swarat, Ortony & Revelle, 2012).Here I report an in-classroom actvity that I created to encourage deep learning core concepts of my infectous diseases course: bacteria are constantly present on human skin, and proper disinfecton is essental to prevent diseases.
On average, human hands harbor more than 150 bacterial species at a density of ~10 7 cells per square centmeter (Fierer, Hamady, Lauber & Knight, 2008;Fredricks, 2001).These bacteria are divided into two communites, the long-term residental fora and the transient fora (Cogen, Nizet & Gallo, 2008).Although diversity of the residental fora varies from one individual to another, hand washing does not signifcantly alter its compositon (Fierer et al., 2008).The transient community, a more-probable source of infectous diseases, is acquired at any given moment afer individuals touch contaminated objects.While hand washing with water removes 48% of transient bacteria, and with soap 82% of them (Burton, Cobb, Donachie, Judah, Vurts & Schmidt, 2011), the remaining bacteria can stll cause infectons.In additon, residental bacteria can be opportunistc pathogens and enter deep tssues when the skin has a cut.Therefore, disinfectng agents must be used under circumstances to prevent the spread of potental pathogens.
In this low-budget two-classroom-period actvity, my students examined the bacteria on their hands, evaluated the efectveness of alcohol wipes on reducing bacteria, and composed a scholarly artcle to report their fndings.Afer implementng the actvity for fve semesters, it is proven successful to 1) foster critcal thinking and creatveness; 2) demystfy the process of scientfc research and publicaton; 3) train students quanttatve skills in decision-making; 4) reinforce scientfc theme knowledge; and 5) promote cooperatve learning and peer review.

METHODOLOGY 2.1 The Experiment (~ 20 min long)
This in-classroom actvity required nutrient agar plates, disposable alcohol pads containing 70% isopropyl alcohol, and Sharpie permanent markers, all of which can be purchased from online stores as ready-to-use products.Nutrient agar plates were stored in a household refrigerator for up to 6 months untl use.These materials were either sterile or disinfectng, therefore posing no health hazards to the students.
On the day of actvity, students were asked to pair up with a partner, and each pair was given a set of the abovementoned materials.One student in the pair played the instructor role by labeling the plate, reading aloud the instructons, tracking the tme, and ensuring accuracy of the conducts.The other student was the experimenter.I frst briefy lectured the following concepts: 1).Bacteria are omnipresent; 2).Humans have a residental community that is generally harmless and cannot be removed by simple washings; 3).Bacterial can quickly multply to form a visible mass called colony on the nutrient agar surface.I then asked students if they recalled their last vaccinaton experience, whether their doctors wiped their skin with an alcohol pad before giving the shots, and informed them that the actvity might explain why wiping the skin before injecton was necessary.Since most students had not seen an agar plate previously, I specifcally pointed out locaton of the growth medium, explained the importance of labeling near the edge of the botom cover, and walked students through the experimental procedure.Additonally, I warned students not to press the agar surface with more pressure than necessary to leave a fngerprint so as to avoid creatng cracks on the agar surface.To minimize contaminaton from microbes and their spores in the air and in human mouths, I asked students to keep plates covered unless opening was necessary, and to restrain from sneezing or talking directly to the agar surface.Afer the short lecture, I lef a recipe-type experimental procedure and a schematc cartoon on the white board while students performed the experiment.
In the experiment, students frst divided each nutrient agar plate into 4 sectons and labeled them with numbers.Experimenters of each group then gently pressed their lef index fngers onto the agar surfaces of quadrant 1 for 2 seconds, immediately followed by a second press in quadrant 2 for 2 seconds with the same fnger.The same student in each group contnued to press his/her right index fnger in quadrant 3 for 2 seconds, followed by a thorough cleaning (10 second wiping) of the right index fnger with an alcohol pad.The wiped fnger was then pressed on quadrant 4 of the plate for 2 seconds.Finally, students returned plates to the front desk and secured them by taping the covers to the botoms of the plates.These plates were brought back to my ofce, and incubated at room temperature for 3 days afer which growth paterns with best contrast were observed.If a class meets once a week, plates can be stored upside down in a refrigerator afer the 3 day incubaton.To provide students with visual records for later data analysis, I took pictures of the plates and uploaded them to the course website.

Observaton And Data Recording (~ 20 minutes)
In the next class period, agar plates were returned to students for observaton.I instructed students to not open the covers since bacteria from students' hands had grown into large biomass, which made them potental opportunistc pathogens.Students were asked to look through all plates from the entre class to make notce of a general growth patern in the four quadrants before they observed their own plates.They were asked to describe colonies on their plates by comparing them with the morphologic views of common colony types (Holt, Krieg, Sneath, Staley & William, 1994), and by making notes of their colors and sizes in mm diameter.They also counted the number of colonies in each quadrant.Since most American students are not familiar with the metric system, I distributed printout paper rulers to students as a reference.
Afer data recording, I collected the plates and brought them back to the ofce for proper disposal.Plates can be autoclaved if an autoclave is available.Alternatvely, they can be submerged in 10% bleach for 15 minutes before draining and discarding in regular trash.

Assignment Instructon in Bullets Assessment Field C I P Q S T W Correct spelling, punctuaton and grammar; correct format of scientfc names
x At least two scientfc citatons from the last 5 years with matching afer-text references in an exampled format x x Informatve and concise ttle, afliaton and detailed contact informaton of the author x x An abstract summarizing the entre paper including objectve, brief method, major results and conclusion x x Clearly marked and complete sectons including Acknowledgements and References x x

Elements of scientfc method (observaton, critcal queston, hypothesis, predicton) logically presented in the introducton secton x x x x
Importance of the study explained x x x Detailed materials and methods in paragraphs in past tense to allow readers precisely repeat the experiment x x Identfcaton of independent, dependent, and controlled variables x x Identfcaton of the controls and explanaton of their purposes x x x Descripton of colony morphology of their own plate in a table format x x x x Speculaton of microbial species found on the plate based on knowledge of common skin microbes and their colony morphologies (citatons are required) x Table 1.Instructons for the scientfc paper assignment and linked assessment felds of scientfc inquiry skills Although many students had writen scientfc reports previously, most stll had difculty understanding the structure of scholarly artcles, thereby limitng their comprehension of these valuable evidence-based informaton sources.In this writng assignment, students were forced to play the role of scientsts, investgatng a problem and communicatng with other experts in the feld about their fndings.Students were asked to complete a publishable scientfc manuscript based on the alcohol wipe actvity, so that they could understand the processes of scientfc research and knowledge diseminaton through frst-hand experiences.Prior to this assignment, a mini workshop was given to help students discern scholarly artcles from popular literature.I explained to students how each secton in a scientfc paper could facilitate communicaton, collaboraton and peer monitoring.I also handed out a general template of scientfc paper and a few sample papers before ofering some suggestons on how to write each secton well.I briefy explained how scientsts without being an expert in mathematcs conduct statstcal analyses using Microsof Excel.I used one example dataset to show students how to calculate the averages and standard deviatons, how to generate graphs to compare values of two groups, how to determine the outliers, and how to use P-value to judge whether a diference observed between two groups was statstcally trustworthy.Since some students had no experience with Excel or confdence in math, I created tutorial videos and posted them on the course webpage.To some students this assignment was intmidatng due to its complexity.To ease the anxiety, I provided very detailed assignment descriptons in bullets as summarized in Table 1.I assigned a point value to each bullet to ensure that students did not omit questons.I also encouraged students to seek external help, including the tutoring center and the library specialists.
For the assignment, students were provided with pictures of 40 select agar plates from previous semesters, and an Excel spreadsheet containing the numbers of colonies counted from each quadrant of the 40 plates.
Students were told that these results were from other student pairs.Students were given two weeks to complete the assignment and asked to work collaboratvely with their partners.

EXPERIMENTAL RESULTS
Afer 3 days of incubaton, bacterial colonies of various sizes (Ø 0.5-5 mm), shapes and colors (pink, red, orange, creamy, white, transparent, black, yellow) were observed on the plates (Figure 1).The most common morphotype showed a white color, circular and convex shape, and size of 0.5-1.5 mm in diameter, matching the descripton of Staphylococcus epidermidis, the most abundant bacteria found on human skin (Cogen et al., 2008).The second most common morphotype is yellow in color, matching the descriptons of another common skin bacterium, Staphylococcus aureus (Cogen et al., 2008).A limited number of plates also showed fungal growth (Figure 1D).To accurately identfy the species of the colonies, if budget allows, 16s rDNA of these colonies can be sequenced and mapped to known reference genomes.
Most plates also showed no microbial growth in the quadrant containing prints from the alcohol wiped fngers.
Occasionally microbial growth was found in non-fngerprint areas, likely due to exposure of the growth medium to ambient air or student's breath.Comparison of the colony reducton rates from frst press to second press yielded a p value much smaller than 0.01 between the lef fnger and the wiped right fnger, suggestng that the observed diference was statstcally trustworthy, and that it was the alcohol wipe that had made a diference rather than some random factors.

ASSESSMENT AND OUTCOMES 4.1 Student Engagement
The primary objectve of this actvity was to minimize student's fear of science and inspire their curiosity (Figure 2).Based on surveys conducted at the end of each semester, this goal was successfully reached.
Students considered this exercise more interestng than other engaging pedagogies ofered throughout the semester including games, group discussions, movies and feld trips.They were impressed by the quantty and diversity of microbes on their hands, and were excited throughout the process since it didn't require too much previous knowledge in microbiology and they were doing research to learn about themselves.Many were eager to share pictures of their hand bacteria with friends and family via popular social media such as Facebook.Since students perceived bacteria as germs that cause diseases (although >99% of them do not cause human illnesses), this exercise also reinforced their hygienic habits and taught them efectve ways to remove bacteria.
As for the writng assignment, many students considered it challenging and tme consuming, yet they selfreported strong satsfactons for the many skills that they have learned from this mock writng experience.They reported that the exercise enhanced their independence of work, tolerance for obstacles, readiness for new challenges, growth of self-confdence, and sense of accomplishments

Critcal Thinking And Creatveness
Based on students' submited assignments, they have demonstrated the critcal thinking skills as well as creatvity in many ways.For example, some students notced a diference between the average numbers of microbes found on their lef hands and right hands during the frst presses, and hypothesized that the patern was caused by individual's preference of hand use.Most students were able to make logical speculatons of bacterial species found on the plates based on the common microfora on human skin published in recent scholarly artcles and the descripton of these microbes in reference textbooks.Several students pointed out that the speculaton needed backup from more accurate biochemical analyses.Students were also able to spot the major faw of experimental design: since the control fnger was not wiped, it was not possible to discern whether the removal of microbes was due to the wiping acton or because of alcohol.Students proposed interestng and relevant future studies based on results from the experiment.Some proposed a hand-shaking experiment to study whether microbes could be easily exchanged between individuals; Some suggested to test the efectveness of other commercial disinfectng products such as hand sanitzer gels and wipes; Some wanted to identfy the bacterial species and compare the gender, handedness, race and ethnic background diferences.

Scientfc Process, Informaton Literacy And Communicaton
The experiment and subsequent scientfc paper writng assignment was a deep-learning role-play experience for students.Afer conductng the experiment, collectng and analyzing data, and making a statstcally relevant conclusion, they have acted as a junior scientst, and have gone through each step of the deductve scientfc method.Role-play simulaton is a proven highly efectve tool for process understanding (Nestel & Tierney, 2007), and has become a popular approach to engage students in non-major courses, especially politcal science and religious studies (Kelly, 2009).At the end of the semester, students who have gone through this actvity where they played the role of a scientst showed a beter comprehension of scientfc processes in solving scientfc and non-scientfc problems when they were given diferent scenarios to analyze elements of the scientfc method.
By actng as a scientst writer, students also developed a beter understanding of the journal artcle structure, and subsequently a set of skills required by informaton literacy.Students realized the following: 1 ) The fxed format of scientfc papers helps readers to quickly locate informaton and understand the otherwise difcult-toread jargon-flled artcle; 2) Authors must provide complete and detailed contact informaton to allow readers seeking collaboraton or answers to their questons; 3) The funding source listed in the acknowledgements secton may reveal a confict of interest that downgrades the value of a paper; 4) Only original, authoritatve, objectve and valid data are allowed in scientfc scholarly artcles; 5) Conclusion of a study are usually drawn upon quanttatve reasoning; 6) Scientfc research doesn't always happen in the perfect sequence of deductve scientfc method, but scientsts present their data in that order to avoid confusion and enhance readability.In the writng assignment, students were required to cite scholarly references.Google Scholar was the search engine most students used.Their understanding of the anatomy of a scholarly paper helped them to fnd and flter informaton from relevant reference artcles.They also followed certain citaton styles and paraphrased major fndings from these artcles to support their own statements.Later assignments of the semester all required citatons from scholarly artcles, and this exercise prepared students to become comfortable in searching and citng from scientfc literature, and even critquing some studies as what peer scientsts would do.
In additon, this assignment enhanced students' communicaton skills through writng and visually presentng informaton in images, graphs and tables.

Quanttatve Reasoning
In science, a conclusion is valid only when it is supported by statstcs.One individual agar plate may show no reducton of bacterial colonies between two presses, but it's the overall trend from all of the replicates that allows scientsts to make a meaningful conclusion.From the writng exercise, students learned to identfy outliers and conduct simple statstcal analyses.They were able to use the P-value to determine whether a diference observed between the control and treatment groups was from random efects or the treatment.They also learned the diference between correlaton and causaton (e.g., the presence of alcohol in the pad is correlated with reducton of bacteria on the wiped fnger, but it may not be the cause of the reducton).

Theme Knowledge
Theme of this scientfc inquiry class was infectous diseases.This actvity helped students to understand topics including bacterial growth, human normal fora, food poisoning, and the control of microbial growth with antmicrobials.

Informal Cooperatve Learning
Students who took this course were mostly lower grade college undergraduate students, and most of them came from diferent felds of study.It was easily recognizable that these students have diferent strengths and weaknesses.To foster peer learning, students were assigned to random pairs for writng the scientfc paper.
Compared with the few students who opted to work on the assignment alone, students who worked collaboratvely completed the writng with notceably higher quality.Working with a partner allowed students to beter grasp related course materials and follow the assignment instructons.For example, when one partner overlooked a problem or made a careless mistake, the other can catch it during proofreading; the student beter at math and creatng charts may compensate well for the partner who is beter at writng and searching supportng informaton but weak in math.To avoid unfairness in work share and schedule conficts, I set aside one classroom period to allow collaboratve work and supervised their partcipatons.This small group informal collaboraton in fact mimics the collaboratve nature of scientfc research in the real world: scientsts with diferent expertse work together for complex projects and publish together as a group.This is also the preferred working model for productve businesses at a tme when work has become more interdisciplinary and complicated (Barron, 2000).Therefore, the teamwork skill that students learned from this actvity will eventually beneft them when they transiton from school to workplace.

Cost Of Actvity
The cost per student for the entre actvity was less than $1 when students worked in pairs and bleach was the chosen method of disposal.If the professor wants to make the actvity more hands-on and more classroom tme is available, students can prepare their own nutrient agar plate with agar powder and a microwave.Either way, this actvity is safe for college-aged students and easy for the professor to set up.Its cost efectveness may be especially desirable for insttutons that are restricted by funding, and/or laboratory spaces.

CONCLUSIONS
In conclusion, this inexpensive, simple in-classroom experiment and its associated assignment proved to be an efectve method in teaching key concepts of scientfc inquiry.Students were actvely engaged, and gained specifc skills in research design, hypothesis formulaton, data analysis, presentaton, and quanttatve reasoning.
The reported experiment and its associated teaching-evaluaton methods can be easily adapted to other science disciplines.For example, in physics, students may throw eggs connected to diferent shaped parachutes of the balcony of a building to test which shape has the highest drag force; in chemistry, students may ttrate to determine whether the concentraton of an actve ingredient is higher in one commercial detergent than a compettor product.
x x Reportng the trend observed from all 41 plates x x Image of a representatve plate with an informatve fgure legend x x x Calculaton and discussion of the data outliers x x A column graph to compare the efectveness of microbial removal with and without the alcohol pad x Calculaton and interpretaton of error bars and the p value x x x Discussion of experimental design limitatons x x Proposal of a future experiment based on current results x x x A conclusion based on the statstcal analysis of all plates x x x Note: C, critcal thinking; I, informaton literacy; P, scientfc process; Q, causatve and quanttatve reasoning; S, social connectons; T, theme knowledge; W, writen communicaton

Figure 1 .
Figure 1.Representatve results showing various microbial colony types found on student hands.Quadrants 1-4 represent lef index fnger frst press, lef index fnger second press, right index fnger frst press and right index fnger second press afer applying alcohol wipe, respectvely.Please note that quadrant 1 of plate D showed a penny sized fungal colony . It forced them to do more literature research and delve more deeply into the theme subject.Many students also posted their scientfc paper on an e-Portolio webpage to showcase their critcal thinking and writng skills to potental employers.In additon, similar to what Harrison, Dunbar, Ratmansky, Boyd and Lopato (2010) reported, a few students revealed that they would reconsider science as a career choice.

Figure 2 .
Figure 2. Student Engagement.Top: Students performing the alcohol wipe experiment; Botom: Students observing colony morphology during the second classroom period