Mycology: Yeasts and Dimorphic Pathogens

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Author: Elmer W. Koneman, MD
Reviewer: Barbara Cebulski, MS, MLS(ASCP)CM

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Continuing Education Credits

  • P.A.C.E.® Contact Hours: 2 hour(s)
  • Florida Board of Clinical Laboratory Science CE - General (Microbiology/Mycology/Parasitology): 2 hour(s)

Objectives

  • Define terms that are used to describe morphologic features of molds.
  • Describe preliminary identification methods for various yeasts.
  • Identify yeast species by observing the appearance of the colony morphology and through microscopic appearance.
  • Interpret various yeast patterns of growth on cornmeal agar.
  • Discuss various diseases that are associated with yeasts.
  • Define "dimorphic fungi" and identify dimorphic pathogens.
  • Describe microscopic and colony morphologies that aid in the identification of dimorphic pathogens.
  • Identify sources and diseases that are associated with dimorphic pathogens.
  • Recognize saprophytic molds that can mimic morphologic features of dimorphic pathogens and describe methods to inhibit the growth of these saprophytic counterparts.

Course Outline

  • General Information Related to Identification of Molds
      • Introduction to the Identification of Molds
      • Terminology Related to Morphologic Features of Molds
  • Morphologic Features of Yeast
      • Preliminary Identification Methods for Various Yeasts
      • Morphologic Features of Yeast Colonies
      • Microscopic Morphologic Features of Yeast
      • Malassezia
      • Which of the organisms listed below has the unique property of producing germ tubes when fetal bovine serum is lightly inoculated with the yeast isola...
      • The growth of the yeast-like colonies shown in the upper image was obtained on blood agar from a skin culture only in the area overlaid by virgin oliv...
  • Yeast Identification Using Cornmeal Agar
      • Interpretation of Growth Patterns on Cornmeal Agar
      • Examples of Cornmeal Agar Morphologies
      • Match each of the cornmeal agar morphologies listed in the drop-down box with the name of its corresponding yeast species on the right.
      • Match each of the fungal species listed below with the appropriate category, indicating whether or not it has the capability of producing pseudohyphae...
      • A yeast identification system gave a biotype number for an unknown isolate that did not differentiate between Candida tropicalis and Candida parapsilo...
  • Extending the Preliminary Identification to Full Identification
      • Evaluating the Need for Full Identification of Yeast
      • Recommended Procedure for Identification of Cryptococcus neoformans
      • Arrange in sequence the steps that should be taken to make a definitive identification of Cryptococcus neoformans.
      • The colonies illustrated in this photograph were recovered from a blood culture after 48 hour incubation at 30°C. What is the MOST likely source ...
      • Illustrated in this photomicrograph of a lactophenol blue preparation of a urine sediment is a cluster of yeast cells that were presumptively identifi...
  • Dimorphic Pathogens
      • What are Dimorphic Fungi
      • Microscopic Morphologic Features of the Mold Forms of Various Dimorphic Fungi
      • Microscopic Morphologic Features of the Yeast Forms of Various Dimorphic Fungi
      • Culture Confirmation Methods
      • Histoplasma capsulatum
      • Coccidioides immitis
      • Sporothrix schenckii
      • Blastomyces dermatitidis
      • Paracoccidioides brasiliensis
      • Match each of the names of the dimorphic fungi listed with the names of the animals that most commonly may be related to transmission of disease to hu...
      • The colonies shown in the upper image were obtained on blood agar from a sputum specimen after 10 days incubation at 30°C. The lower image is a l...
      • The growth of the colonies shown in the upper image was obtained on blood agar from a sputum specimen after incubation at 30°C. The lower image i...
      • The colonies shown in the upper image, obtained from a biopsy of an ulcerating skin lesion of the arm, are growing on agar slants of Sabouraud's dextr...
      • The upper image illustrates a subculture of a mold colony suspected of being a dimorphic fungus inoculated to the surface of blood agar and incubated ...
      • Although care should be taken when working with all fungus cultures in the laboratory, personnel are particularly prone to develop laboratory acquired...
      • Which dimorphic fungus may produce black, yeast-like colonies after prolonged incubation at 37°C?
      • Match each of the names of the dimorphic fungal species from the drop-down box with its mold form shown below.
      • The images below are lactophenol blue mounts of the yeast forms of various dimorphic fungi. Which of the images is consistent with an identification o...
  • Differentiating Dimorphic Molds from Saprophytic Counterparts
      • Differentiating Dimorphic Fungi from Saprophytic Molds
      • Inhibiting the Growth of Saprophytic Molds
      • This image illustrates a lactophenol blue mount of a mold recovered after 7 days incubation of brain heart infusion broth. The large macroconidia sugg...
      • Which of the following ingredients is added to culture media to enhance the recovery of the dimorphic fungi by preventing the overgrowth of more rapid...
  • References
      • References

Additional Information

Level of instruction: Intermediate
Target audience: Microbiologists, medical laboratory scientists, medical laboratory technicians, and MLS students.
Author information: Elmer W. Koneman, MD, received his graduate degree from the University of Colorado School of Medicine at Denver, Colorado and is currently Professor Emeritus at their Department of Pathology. He is the author of numerous journal articles and books, including Color Atlas and Textbook of Diagnostic Microbiology, Fifth Edition, 1997(Lippincott) and is presently affiliated with Instructional Design Consultants, a consulting firm specializing in interactive training and distance learning for clinical microbiology.
Reviewer information: Barbara Cebulski, MS, MLS(ASCP)CM is a Program Director for MediaLab, Inc., located in Lawrenceville, GA. She has over 30 years experience in the medical laboratory profession as a technologist, section supervisor, and laboratory manager. She also was employed for nine years by the College of American Pathologists in the Laboratory Accreditation Program. Barbara holds a Masters in Instructional Technology from Georgia State University.
Content information: This course describes and identifies medically important yeast and dimorphic pathogens. Many photomicrographs are used to assist with recognition of organisms in culture and microscopically.

Mycology: Yeasts and Dimorphic Pathogens Keywords

These are the most common topics and keywords covered in Mycology: Yeasts and Dimorphic Pathogens:

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This course is part of:
yeast01
Yeast03
YEAST02
yeast15 big
lollipop conidia
Candida parapsilosis, cornmeal agar mount.  Characteristic is the production of several spider-like colonies, composed of delicate pseudohyphae, produced along the margins of the streak.
dimorphic fungi yeast forms microscopic
question Blastomyces