In principle, this case looks like a good way to talk about cell structure in an introductory course. However, I was VERY disappointed by this case, for several reasons:

(1) In this case, the researchers examine a blood sample microscopically and identify Gram-negative bacteria by their size, presence of DNA and outer membranes! It’s not made clear until later that they used an electron microscope, which is likely to lead to the misconception that a light microscope could be used to perform this analysis. More importantly, it leads to the misconception that electron microscopy would be used to identify an infectious agent. Instead, why not teach methods of identifying prokaryotic and eukaryotic pathogens that might actually be used, such as Gram staining to identify a Gram-negative pathogen?

Author’s Reply: The gram staining method is briefly mentioned in the case as well as in the case teaching notes. In the interest of keeping the slides to a minimum of text and the length to 75 minutes, details about the gram stain as well as microscopy were not written out in detail, but faculty can easily elaborate at length if they so desire.

(2) Why would the researchers look at a blood sample? If this individual has bacteria in her blood, she’s septicemic and will be dead long before the electron microscopy is done. The idea that blood remains sterile except in an extremely serious and widespread infection is valuable for students to learn—instead, this case will again create mis-perceptions. Why not talk about taking appropriate samples for the symptoms and organism under consideration?

Author’s Reply: This case is not designed to cover details of microbiology sampling and is designed for introductory biology courses which never have details on sampling techniques in the textbook. This would make an excellent extension of the case in a microbiology course, though.

(3) The DNA analysis component is clearly intended to teach the importance of molecular genetics in identifying species today, but it’s unrealistic in terms of how molecular analysis might be used. PCR would be much more realistic here! Antibody-based tests could also be mentioned.

Author’s Reply: Again, students at this stage of an introductory biology case have not learned about PCR or antibody tests, so it would be unnecessarily confusing to mention them here.

(4) The case has one of the students’ mothers sending all manner of antibiotics, antivirals and other chemotherapeutics, which the students administer rather indiscriminately based on the results of their analysis, and also take prophylactically. Obviously, this aspect of the case is meant to be somewhat facetious, but rather than seizing an opportunity to educate about proper use of antibiotics, it does the opposite.

Author’s Reply: Absolutely, and the case specifically highlights how useless it was to use antibiotics without knowing what the disease organism is. The more serious issues of antibiotic resistance would make an excellent follow-up discussion in later lectures in the course.

Rather than showing how biological knowledge might be used in an actual case, this study exaggerates the case so much that is seems entirely artificial. Further, it may create more misconceptions than it cures. This case does not seem to be of the quality typical of NCCSTS. I suggest it be greatly revised or removed from the site.

Comments submitted 11/04/2008 by:

Jonathan Visick
Department of Biology
North Central College
Naperville, IL 60540
jevisick@noctrl.edu