Using Stain Tests to Identify Fungi & Actinomycetes Ch 11 Lesson 3 PDF

Using Stain Tests to Identify Fungi & Actinomycetes Learn about the staining tests used to identify fungi and actinomycetes. This lesson will go over procedures, turn around time for results, uses, and the similarities and di!erences between fungi and actinomycetes. Staining Tests and Procedures f...

Using Stain Tests to Identify Fungi & Actinomycetes Learn about the staining tests used to identify fungi and actinomycetes. This lesson will go over procedures, turn around time for results, uses, and the similarities and di!erences between fungi and actinomycetes. Staining Tests and Procedures for Fungi There are several tests that can be utilized to detect eukaryotic, spore-producing organisms. KOH Preparation If the objective is to simply detect the presence of fungi, a potassium hydroxide (KOH) preparation, also known as a fungal scraping or fungal smear, is a suitable "rst step. Obtained samples are placed on a slide with a small amount of 20% KOH dropped onto it. Samples can originate from the patient's nails, hair, skin, or even from a vaginal swab. After the slide is brie#y heated, the KOH solution will dissolve non-fungal constituents, thus leaving behind any evidence of fungal hyphae and yeast cells. A KOH exam is typically recommended for those experiencing a persistent rash that has not responded to corticosteroids and/or those with extreme itching. This test is useful for identifying fungi responsible for jock itch, fungal nail infections and ringworm. For inconclusive results, a biopsy of the skin may be necessary.  Ringworm Ringworm infection infection with with circular circular red red rash rash and and raised raised edges edges used used for for skin skin scraping scraping in in KOH KOH preparation preparation Calco!our White Stain Though KOH preparation provides quicker results, a Calco!our white stain can still be employed to stain and observe the presence of fungi as well as parasites. Similar to the KOH prep, skin and nail scrapings and vaginal swabs are appropriate samplings to use; however, the Calco#uor white stain speci"cally binds to a fungi's cellulose cell wall and chitin, which makes up the cell wall, and glows a bright green color when analyzed under UV light. Though it is a non-speci"c test, it has proven to be sensitive. Fungal Culture A fungal culture places an obtained sample upon a nutrient medium, incubated and observed for growth. This method is very useful in determining a fungal infection and the speci"c culprits. Depending on the fungi present, fungal culture results can take up to several weeks.  Fungal Fungal growth growth that that has has been been incubated incubated on on nutrient nutrient agar agar Staining Tests and Procedures for Actinomycetes Much like fungi, actinomycetes are members of an order of spore-producing and "lamentous bacteria; however, they are di!erent in that they are prokaryotic Gram-positive bacteria that contain peptidoglycan within their cell walls. Because they can sometimes be mistaken for one another, there are other tests available to speci"cally detect for actinomycetes, Nocardia being the most common organism. Gram Stain Many actinomycete organisms can be observed via the Gram stain technique owing to their Gram- positive nature. The procedure is as follows: 1. Transfer obtained sample onto a slide with crystal violet solution. 2. Wash the slide with water and administer iodine, which is used as a "xative. 3. Wash the slide and use alcohol as a decolorizer to remove the crystal violet stain from Gram-negative species without a!ecting the staining of those that are Gram positive. 4. Wash the slide again and add safranin (the counterstain). 5. Wash for the last time and observe results. Once the Gram stain is complete and purplish-blue stained organisms are observed, this is evidence of Gram-positive bacteria. Aside from Gram staining properties, organisms' shape and size can also be noted, which aids in ruling out certain organisms.  Positive Positive Gram Gram stain stain showing showing dark dark purple purple staining staining Ziehl-Neelsen Stain The Nocardia species is set apart from other organisms in that it is a weak acid fast bacteria. This just means it has some capability of resisting decolorization when a staining procedure is underway. A modi"ed acid-fast staining test named the Ziehl-Neelsen stain can potentially be used in detecting the presence of Nocardia. Instead of a crystal violet solution, a carbol fuchsin dye is used as the primary coloring agent. After being rinsed with water, a colorless acid alcohol is dropped onto the slide, rinsed o!, and methylene blue is used to dye the sample. Organisms deemed as acid fast will either appear red or pink. Lesson Summary Though they may have similarities, fungi and actinomycetes are two vastly di!erent organisms. Eukaryotic fungi can be stained using: a KOH preparation, which provides quick results and makes use of samples from the skin, hair, or nails. Calco!uor staining staining agent binds only to fungal constituents. This method can also be useful for parasites. a fungal culture where a sample is put on a nutrient medium, where it is incubated and observed for growth. Results may take a few weeks. Actinomycetes, members of an order of spore-producing and "lamentous bacteria, can undergo a Gram stain where they will appear purple (because they are Gram positive) under a microscope. A speci"c species of actinomycetes, Nocardia, is deemed as acid fast and can potentially be stained using a modi"ed acid-fast staining technique called Ziehl-Neelsen that uses carbol fuchsin dye.  Like this lesson  Share  Explore our library of over 88,000 lessons Search Search Courses & Lessons  Browse Browse by subject 