13: SURVEY OF FUNGI
- Page ID
- 157075
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Identify and describe the microscopic structures of medically important fungi, including yeast cells, hyphae, conidia, zygospores, and asci, using prepared slides and appropriate magnification.
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Explain the relationship between fungal morphology and pathogenic potential, with emphasis on opportunistic infections caused by species such as Candida albicans and Aspergillus spp.
BACKGROUND
Fungi (a group of eukaryotic organisms that includes yeasts, molds, and mushrooms) are important to both the environment and human health. While fungi are known for their roles in nutrient recycling and food production, they also play a major role in medicine—sometimes as life-saving allies, and sometimes as harmful pathogens. For future healthcare workers, understanding how fungi function in the body and in clinical environments is essential.
Many fungi are opportunistic pathogens, meaning they typically don't cause disease unless the host's immune system is weakened. Fungal infections, or mycoses, can affect the skin, mucous membranes, lungs, bloodstream, and internal organs. These infections are often more difficult to treat than bacterial infections because fungal cells are structurally similar to human cells, which limits the number of safe and effective drug options. In addition, drug resistance and toxicity are ongoing concerns in antifungal therapy.
One of the most common fungal pathogens is Candida albicans, a yeast that normally lives in the human mouth, digestive tract, and vaginal area. When conditions change—such as during antibiotic use, pregnancy, diabetes, or immune suppression—Candida can multiply out of control. This overgrowth can lead to infections such as oral thrush, vaginal yeast infections, or more serious bloodstream infections called invasive candidiasis, especially in hospitalized patients.
Another important fungal group is Aspergillus, a mold commonly found in soil, air, and decaying vegetation. Aspergillus fumigatus is known to cause allergic reactions in some individuals and can form fungal balls in the lungs of those with pre-existing conditions. In more severe cases, it can invade the lungs and spread through the bloodstream, particularly in people receiving chemotherapy or organ transplants. Aspergillus flavus is a related species that produces aflatoxins—dangerous compounds that can contaminate stored food and contribute to liver disease when ingested. Schizo-saccharomyces, a fission yeast used in fermentation processes, is not commonly pathogenic but may occasionally be associated with infections when introduced into a disrupted or immunocompromised system. Similarly, Penicillium notatum, while not typically harmful, is famous for its contribution to medicine. This mold was the original source of penicillin, the first antibiotic, which revolutionized the treatment of bacterial infections. Today, other fungi are used to create immunosuppressive drugs, cholesterol-lowering agents, and powerful enzymes for laboratory testing and biotechnology.
As fungal infections become more frequent in hospitals—due to the use of catheters, ventilators, and immunosuppressive treatments—it is increasingly important for healthcare professionals to recognize their signs and understand their sources. Fast and accurate diagnosis, combined with knowledge of fungal biology, is essential to protecting patient health.
In this lab, you will examine key fungal structures and learn how to identify medically relevant species under the microscope. This experience will help you connect the biology of fungi with the diseases they can cause, strengthening your diagnostic skills and preparing you for clinical practice.
Pay attention to the characteristics and appearance of the organisms, structures and features you observe and draw, you may be asked to identify them on the lab exam.
MATERIALS (per student)
Prepared slides of various fungi
METHODS/PROCEDURES
- Draw what you observe as you look through the microscope from each of the six slides in the results section. The final magnification for each organism is indicated in the table below.
- Label the structures and or features indicated in the table for each organism.
- Keep in mind that fungal cells are much larger than bacterial cells. Some of the structures you will observe—like hyphae or spore-bearing bodies—are composed of many cells and are best viewed at lower magnifications. Not all slides are perfect, so don’t be discouraged if some features are
- harder to see. Ask your instructor for help if you’re having trouble locating key structures. Use caution when focusing. Fungal slides are often thick, and it’s easy to damage them by accidentally striking the glass with the microscope objective. Move slowly and carefully to avoid breaking the slide or scratching the lens.
Rhizopus and Aspergillus have very thick cover slips.
DO NOT USE ANY MAGNIFICATION HIGHER THAN LISTED BELOW
|
Rhizopus |
100x | Draw the zygospores (not conidia) |
| Aspergillus | 100x | Draw conidia covered with spores |
| Penicillium | 400x | Draw the branched conidia |
| Candida albicans | 1000x | Draw both hyphae & round yeast type cells |
| Saccharomyces cerevisiae | 1000x | Draw budding (dividing) cells |
| Schizo-saccharomyces | 1000x | Draw ascus with spores inside |
The following is to be completed during lab then turned in on Canvas as a PDF
*If you are using an iPad or tablet you will need to take screen shots of your competed work, save the screenshots as one PDF then submit them on Canvas by the due date designated on Canvas.
*You can also print out the entire exercise to bring to lab with you. If you choose to complete the lab on paper, take pictures of the completed results and conclusions sections only, save them as one PDF, then submit to Canvas by the due date designated on Canvas.
FUNGI
NAME ______________________
EXPECTATIONS
Based on your background reading, what differences do you expect to notice between fungal cells and
bacterial cells under the microscope?
Why might some fungal slides be more easily observed at low magnification rather than high
magnification?
RESULTS
CONCLUSIONS
1. How did the appearance of Candida albicans differ from that of a mold like Aspergillus or Penicillium?
2. Describe two features you observed that differentiate Saccharomyces cerevisiae from Schizo- saccharomyces
3. If you were given an unknown fungal sample from a patient, what observations from today’s lab would help you begin to identify it?
4. Explain one similarity and one difference between endospores and fungal spores
5. Which fungal species in today’s lab are considered opportunistic pathogens? What conditions might allow these fungi to cause infection?