Identifying Fungi & Actinomycetes in Macroscopic Settings PDF

Identifying Fungi & Actinomycetes in Macroscopic Settings In this lesson, learn about macroscopic methods to identify fungi, including yeasts, molds, dimorphic fungi, and dermatophytes, as well as the fungi-like bacteria actinomycetes. Identifying Fungi Macroscopic methods for identifying fungi of...

Identifying Fungi & Actinomycetes in Macroscopic Settings In this lesson, learn about macroscopic methods to identify fungi, including yeasts, molds, dimorphic fungi, and dermatophytes, as well as the fungi-like bacteria actinomycetes. Identifying Fungi Macroscopic methods for identifying fungi often involve growing the fungi on a PDA plate, a potato dextrose agar plate, which is a petri dish with potato dextrose as the food source, one that allows most fungi to grow. The growth patterns on the plate can help to identify the fungi. But di!erent types of agar can also be used to identify the speci"c type of fungi. Identifying Yeast An important test to start determining the phenotype of yeasts is to determine if the yeast can use nitrogen or carbon as its sole source of food. The yeast in question is put onto the dye pour-plate auxanogram (DPPA). The nitrogen and carbon are added with the agar and a pH dye indicator in a tube; it is then poured in a slant, and the organism is suspended in the medium. Any growth from nitrogen or carbon will cause the pH of the agar to change, thus changing the color of the agar. This can allow you to narrow down the phenotype of the yeast. Having Having the the agar agar in in aa slant slant in in the the tube tube gives gives more more growth growth area area for for the the yeast yeast Identifying Mold Macroscopic features of molds include looking at the growth patterns of the colony. This includes identifying the color, growth rate, and shape. Molds are often grown on Sabouraud's glucose peptone agar. The exact composition of the agar is important to standardize the growth rate of the mold, so it is important to ensure that you are always getting the agar from the same supplier. Identifying Dimorphic Fungi A dimorphic fungus can have a mold phase and a yeast phase. Historically, the easiest way to identify dimorphic fungi is by forcing the fungi into the yeast phase, but many methods can be done now without needing additional manipulation of the fungi. There are three main dimorphic fungi: H. capsulatum: can take many weeks to mature, white or tan in color and #u!y B. Dermatitidis: also starts white and #u!y but will turn yellow as it ages Coccidioides: a smooth, large colony that is tan in color Identifying Dermatophytes Dermatophytes are also grown on Sabouraud's glucose peptone agar, but antifungal and antibacterial agents are added to retard the growth of other compounds. Dermatophytes prefer to utilize protein as a food source and will change the pH to be more alkaline, thus changing the color of the plate. They are often a white, light-yellow tan color and have a cotton or powder appearance. Identifying Actinomycetes Actinomycetes are bacteria that form "laments and spores like many fungi. It forms a leathery or smooth colony that is white in appearance or a creamy-colored pinpoint, powdered-looking colony. It grows in seawater agar. Lesson Summary Fungi can be identi"ed by looking at the growth patterns on a PDA plate, which is made from potato dextrose. Yeast is identi"ed using a dye pour-plate auxanogram (DPPA), which sees a color change due to growth from nitrogen or carbon as a food source. Mold is grown on a Sabouraud's glucose peptone agar, and then the color, shape, and growth rate can identify the mold. Dimorphic fungi are grown on a plate and identi"ed using color and shape. Dermatophytes also use Sabouraud's glucose peptone agar, but with the addition of antifungals and antibacterials, they prefer protein as a food source and turn the agar alkaline. Actinomycetes grow in seawater agar to form smooth colonies that are white or creamy powdery colonies.  Like this lesson  Share  Explore our library of over 88,000 lessons Search Search Courses & Lessons  Browse Browse by subject 