INTRODUCTORY BIOLOGY 

(BS 130) CASE STUDY  1                                                     Name________________

 

Introduction

Rhizopus species are the most common  etiologic agents of zygomycosis. Host symptoms range from allergic responses to cutaneous infections to systemic disease with invasion of the central nervous system, arterial blood vessels, lungs, gastrointestinal tract, and other parts of the body (Ribes, J. A., Vanover-Sams, C. L., and Baker, D. J. 2000). Rhizopus (oryzae) arrhizus is a human pathogen. Rhizopus stolonifer is considered nonpathogenic (Larone, D. H. 1993). Both of these species can occur as common contaminants on lab media. Speciation is important for epidemiological studies.  Differentiation of species is based upon lack of growth at key temperatures (see Table 1) and microscopic characteristics. Since the less common Rhizopus species are not easily separated by temperature requirements, microscopic characteristics such as the average size of the sporangium, can be used, as indicated in Table 1:

 

Table 1. Temperature and sporangium characteristics used for speciation of the genus Rhizopus.(Larone, D. H. 1993; Ribes, J. A., Vanover-Sams, C. L., and Baker, D. J. 2000)                                                                                             

Organism Sporangium
diameter (Larone)  

Sporangium 
diameter (Ribes)


Temperature
R. oryzae 50-250 um 100-200 um no growth > 46 C
R. stolonifer  150-350 um up to 275 um no growth > 33 C
R. microsporus 40-130 um   about 100 um variable
R. azygosporus    50-100 um  optimal at 25-30 C
R. schipperae    < 80 um  no growth > 50 C

 

 

The Problem

It can be seen that the reported ranges for sporangia diameters vary even for the same species. In practice, ranges for sporangia diameters may be even greater. Thus, how reliable are these measurements for species differentiation? We will examine this question as we attempt to solve the following case.

 

Sputa from a female patient suspected of suffering from zygomycosis was cultured on laboratory media. A mold identified as a Rhizopus species grew on the media. It can now be speciated to determine if the isolate is R. stolonifer or a pathogenic strain. A plate containing a known culture of R. stolonifer is used for comparison. Using a calibrated ocular micrometer, the diameters of 10 different sporangia from each plate are determined (see Table 2). Analyze the data using Excel’s non-matched pairs student's t test to determine if there is any difference between the two cultures.

 

Table 2. Measurements of sporangia diameters for known and unknown Rhizopus cultures.

Observation  # 

Known sporangia
 diameters (um)

Unknown sporangia diameters (um)

1

225

115

2

192

172

3

176

146

4

210

265

5

198

234

6

205

222

7

206

188

8

190

165

9

215

248

10

205

233

                         

Questions

1. What is the experimental treatment in this study?

2. What is the control group in this study?

3. For statistical analysis, a null hypothesis is stated. A null hypothesis  is one of no difference between the control and experimental treatments. State a null hypothesis for this experiment.

4. For statistical analysis, an alternative hypothesis is also stated. An alternative  hypothesis states that there is a difference between  the control and experimental treatments. Write an alternative  hypothesis for this experiment.

5. Are the two groups of data significantly different? Explain.

6. What is your conclusion (are they the same culture or not)?    Explain.

 

Concepts

scientific method

Observation

Question

Hypothesis

Experimental group

Control group

random error

systematic error

Prediction

Experimental design

Experimental (alternative) hypothesis

Null hypothesis

Conclusion

Presentation

Controls

Level of significance

directional (one-tailed)

nondirectional (two-tailed)

Inductive reasoning

Deductive reasoning

Replication

 

Project

 

1. Each student pair will recieve a problem (T-TEST SIGN SHEET) to analyze using the student's t-test.

 

2. Your goal will be to answer the following questions regarding your problem:

a. What is the experimental treatment in this study? (10 pts)

b. What is the control group in this study? (10 pts)

c. For statistical analysis, a null hypothesis is stated. A null hypothesis  is one of no difference between the control and experimental treatments. State a null hypothesis for this experiment. (10 pts)

d. For statistical analysis, an alternative hypothesis is also stated. An alternative  hypothesis states that there is a difference between  the control and experimental treatments. Write an alternative  hypothesis for this experiment. (10 pts)

e. Are the two groups of data significantly different? Explain. (10 pts)

f. What are your conclusions (statistical and biological)?    Explain.(10 pts)


3. Summarize your findings in a report using WORD.(10 pts) Include the results of your excel spread sheet (the data, means, one or two tailed, and probability).(10 pts)

 

4. Use the following form to evaluate your group work. Peer Evaluation Form (20 pts)

 

5. Report is due September 16, at the beginning of the first class. Reports are considered late one minute after class starts. A penalty of 25 points for each day late including the first period.

 

References

Larone, D. H. 1993. Medically important fungi- a guide to identification. 2nd ed. American Society for Microbiology: Washington, D. C.

 

Ribes, J. A., Vanover-Sams, C. L., and Baker, D. J. 2000. Zygomycetes in human disease. Clinical Microbiology Reviews 13 (2): 236-301.