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Mycology TD

QuestionAnswer
Mycology is the study of fungi. Medical mycology is the practice of isolating and identifying yeast and molds from clinical specimens. Humans suffer from a variety of fungal infections ranging from superficial to systemic. Through isolation and identification techniques the causative organism can be determined.
There are four classes of fungi responsible for human infections. These classes are based on sexual cycles which are usually not seen in cultures of clinical materials. Asexual growth (hyphae and asexual cells) is usually used to identify the organism isolated in clinical laboratory cultures. The classes are Ascomycetes, Deuteromycetes, Zygomycetes, and Basidiomycetes.
Safety in the clinical laboratory is important. Molds by their nature can easily become airborne and infect laboratory personnel. The use of a biosafety cabinet is necessary when working with molds. Most biological safety cabinets protect both the worker and the culture from airborne organisms.
The air that enters the cabinet is filter-sterilized by High Efficiency Particulate Air filters (HEPA) before impinging on the work surface and before entering the exhaust system. The cabinet should be located in a quiet area to minimize disruption of the air flow into the cabinet.
India ink is a suspension of carbon particles in a solution of glycerol and water. When combined with pelleted material from cerebrospinal fluid, India ink allows visualization of the polysaccharide capsules of the yeast, Cryptococcus neoformans. done
The pellet from cerebrospinal fluid spec is resuspended and 1 drop is placed on a clean microscopic slide. A drop of ink is placed next to the drop of fluid. Using a large coverslip, the ink drop is touched with the edge and pulled toward the fluid drop. Once the two drops meet the coverslip is pushed away. The coverslip is then allowed to settle onto slide. This technique will provide areas of varying ink densities which enhance the visibility of encapsulated yeast. Examine at 400X magnification.
A 10% potassium hydroxide (KOH) preparation is used when specimens such as hair, nails, skin or tissue are to be examined for fungal elements. KOH digests the host cellular material allowing the fungal elements to be more easily seen The fungal hyphae appear as long strands that may be septated and branched. The hyphae will be seen to cross the cell walls of the epithelial cells. Budding yeast and pseudohyphae may also be seen on KOH preparations.
Place specimen on a clean microscope slide. Add a drop of 10% KOH. Place coverslip on drop. Allow preparation to remain at room temperature for 5-20 minutes. Examine under the microscope at 400X magnification.
For a more sensitive direct exam of clinical material, calcofluor white can be added to the traditional 10% KOH preparation. Calcofluor binds to the chitin in fungal cell walls. The bound compound fluoresces when exposed to UV light. The procedure is same as that for the KOH exam. Examine under the fluorescent microscope at 100-400X magnification. The image shows fluorescent strands of hyphae, notice the clearly visible septa and parallel walls.
A direct Gram stain of clinical material can be the first indication of the presence of fungi. The intensity of staining of fungi may vary from negligible to strongly gram-positive.
The Gram-Weigert stain is used to detect Pneumocystis carinii. The Gram-Weigert stain is used to detect Pneumocystis carinii. P. carinii cysts, which stain blue with Gram-Weigert, are round to oval in shape.
Histologic stains are useful to demonstrate fungal elements in host tissue. A variety of stains are used, examples include the Gomori methenamine - silver nitrate stain and the Papanicolaou stain.
A variety of specific fungal media have been developed 2 isol. & grow yeast & molds. Choice of culture media 2 be used is dependent upon type of clinical specimens, patient history & organisms 2 be isolated. Further considerations are the mycologist's e Isolation media include: Sabouraud's dextrose agar, brain heart infusion agar.... Media can be supplemented with sheep blood &/or antimicrobial agents to enhance recovery of certain fungi. Cultures should be incubated @ 30ºC and are usually held for 4-6 w
Antibiotics such as gentamicin or chloramphenicol are used to inhibit the growth of bacteria. Media containing cycloheximide will inhibit the growth of some saprophitic fungi. Brain heart infusion agar with sheep blood is used as an enriched medium to isolate the the more fastidous fungi.
Most yeasts form visible colonies within 2-3 days. Yeast colonies vary in color, shape, and texture. Species identification cannot be accomplished solely with visual inspection. Identification requires additional testing.
Different species of yeast produce colonies with characteristic colors, such as white, cream, tan, pink, or coral. Done
Most yeast colonies have smooth edges while others can produce irregular (spidery) edges. Smooth convex surfaces are common, but some species have colonies with folded surfaces.
Different species of yeast can produce characteristic surface textures including smooth, pasty, mucoid, moist or dry. Done
Occasionally, more than one type of yeast may be present on routine culture. Differential agars can be used as primary isolation media or as subculture media to separate similar looking yeast by color.
The wet mount is used to determine if a colony is yeast or bacteria. Yeast are easily differentiated from bacteria by their larger size.
Place a drop of water on a clean microscope slide. Pick an isolated colony to be examined. Mix colony in water to produce a light suspension. Place coverslip on drop. Examine under the microscope at 400X magnification
The germ tube test is a rapid method to distinguish Candida albicans from other yeast. The germ tube is the initial growth of true hyphae. It grows straight out of the cell and the base is not constricted, unlike pseudohyphae which are elongated buds.
Make a light suspension of the unknown yeast in calf serum. Incubate at 35ºC for 2-3 hours. Prepare a wet mount of the suspension and examine at 400X magnification. The germ tube test is a rapid method to distinguish Candida albicans from other yeasts.
For identification of Candida albicans, it is important to distinguish germ tubes from pseudohyphae. A germ tube grows straight out of the cell with parallel walls. Pseudohyphae grow as an elongated bud with a constricted junction.
Yeast morphology agar, such as cornmeal agar with Tween 80, can be used to demonstrate pseudohyphae, true hyphae, budding cells and chlamydoconidia Done
Using an inoculating needle or loop, make 3 or 4 streaks of the yeast on the surface of the cornmeal agar. Make 3 or 4 streaks of yeast on surface of cornmeal agar. Cover the streaked area with a flamed coverslip. Incubate at room temperature for 2-3 days. Following incubation, remove lid and place plate on microscope stage. Examine at 100-400X..
When cultured, certain diploid yeasts undergo meiosis and produce packets of 4 to 8 ascospores. Depending upon the orientation of the packet, all four ascospores may not be visible. Demonstration of ascospores is helpful in identifying these yeast. On routine Kinyoun acid-fast stain, ascospores stain red and vegetative cells stain blue.
Assimilation tests are used to determine the ability of a yeast to use a carbon or nitrogen source for growth. Assimilation is indicated by tubidity in an individual cupule.
Automated instruments use a variety of biochemical reactions and a computerized data base to determine the yeast identification. Done
Enzymatic tests are used to detect the presence of enzymes that degradate specific substrates. Positive enzymatic reactions are indicated by color changes.
Often it is necessary to supplement routine indentification tests. These additional tests may include: nitrate assimilation, melanin production on caffeic acid (bird seed) agar, fermentation of carbon sources, and urea hydrolysis.
Molds form filamentous colonies of various colors and textures. The filamentous growth is called a mycelium. The mycelium is composed of individual strands of hyphae. Aerial hyphae grow above the surface of the agar and give texture to the colony. Vegetative hyphae grow into the agar like roots.
The appearance of colonies on culture media varies depending on the organism. Typically, bacterial colonies appear first, followed by yeast and molds. Within the mold group, growth rates can also vary greatly from appearing in 2-3 days to 2-3 weeks.
The colors of the colony are often the first clues to the mold's identification. Colors range through the spectrum including white, brown, red, green, yellow and black. The aerial hyphae (obverse) may have a different color than the vegetative hyphae (reverse). Diffusible pigments may also be present.
The texture of the colony is helpful in identifying molds. The height of the aerial hyphae growing above the surface of the agar gives texture to the colony. Texture can be described as glabrous, velvety, powdery, cottony or wooly.
Differential tests aid in the identification of molds. The presence or absence of growth on differential media or color change due to pH may suggest specific species. ie, bromcresol purple-milk solids-glucose (BCP-MSG) agar can be helpful in differentiating molds that cause ringworm (dermatophytes). Nutritional requirement tests using Trichophyton agars are used to separate Trichophyton species. The amt of growth on each agar indicates a specific nut. need.
Various techniques and stains are used to visualize the microscopic features of molds grown on culture media. The use of a biosafety cabinet is necessary when performing these techniques. Heavy-gauge wire hooks and dissecting needles are used to manipulate mold colonies
A variety of stains are used to enhance the hyphial and reproductive structures of molds. Two commonly used stains are lactophenol cotton blue and lactofuchsin.
The traditional way to examine an isolate is to perform a tease preparation; however, considerable disruption of the hyphae and the reproductive cells occurs. Begin by placing a drop of stain on a glass slide.
Using a sterile heavy-gauge needle or hook, pick a small sample from mold colony to be examined. Aerial and vegetative hyphae should be included, avoiding white sterile hyphae on the periphery
Transfer sample to the stain. Using 2 needles, in a scissoring motion, tease apart the sample, until a separation of hyphal elements is achieved.
Add a coverslip to the teased sample, pressing down on the coverslip, if necessary, to flatten sample and evenly disperse stain under coverslip. Examine the preparation under 200 - 400X magnification.
A scotch tape preparation is less disruptive than a tease preparation, providing undisturbed morphologic detail of a mold. Begin by placing a drop of stain onto a clean microscope slide.
Touch a folded piece of clear tape to the colony Place section of tape containing mold sample into the stain and carefully press ends of tape onto the slide. Add another drop of stain on top of the tape. Cover drop with coverslip. Examine slide at 200 - 400X magnification.
The least disruptive method to examine fine morphologic details of a mold colony is to perform a slide culture. In the coverslip sandwich method, the mold grows on a coverslip which is later placed in stain. Begin by using bent wire hook to pick up a portion of the colony. Innoculate the agar surface in straight line. Multiple inoculation sites can be made on the same plate. This will allow a culture to be examined over a period of weeks as culture matures.
At the site of the inoculated line, place a flamed coverslip at an acute angle into the agar surface. When the growth appears mature, pull one of the coverslips from the agar. Place the coverslip onto a drop of stain on a microscope slide. Place a second drop of stain onto the coverslip. Place a second larger coverslip onto the drop. Examine the preparation under 200 - 400X magnification.
The hair perforation test is useful in differentiating dermatophytes. The hair perforation test is performed by inoculating the unknown organism onto sterile hair in a solution of sterile water supplemented with 10% yeast extract. Incubate at room temp. The presence of cone-shaped perforations on the hair shaft is a positive test. The absence of perforations after 4 weeks of incubation is considered a negative test.
Once the microscopic preparations are made and stained, it is necessary to examine them for the unique morphologic features that define different molds. The basic structure of a mold is the hypha. These tubular filaments can be segmented, (septate) or non-segmented (non-septate).
Conidia are asexually produced cells that disperse and give rise to new fungal colonies. Conidia are produced from within the hyphae or from special structures produced by the hyphae. Conidiogenesis, the process of condial formation, occurs in many ways which are reflected in the terminology used to describe the types of conidia
Blastoconidia are formed by budding. Buds are produced by de novo growth from the mother cell. This is the manner in which most yeast cells reproduce. Some molds have a yeast phase in which they reproduce by the formation of blastoconidia
Annelloconidia are formed by budding that leaves ring-like scars on the mother cell (annellide). The ring-like scars are useful morphological features which help to distinguish molds that produce annelloconidia from other molds
Phialoconidia are formed by budding from a mother cell (phialide) which may be distinguished by a collarette Poroconidia are produced through a pre-existing pore on the mother cell.
Aleurioconidia are formed from a newly formed hyphal branch which then separates from the main hypha by formation of a cross wall. Done
Arthrocondia are formed by structural changes in the cell walls and septa of preformed hyphae. They are produced along the entire length of the hypha. In some species, the arthroconidia are separated from one another by empty cells. Chlamydoconidia are formed by structural changes in the cell walls and septa of hyphae. They can be located terminally or within the length of the hypha. Based on earlier terminology, chlamydoconidia are generally known as chlamydospores
Sporangiospores are formed within a sac-like sporangium located at the end of a sporangiophore (aerial hypha). Sporangiospores are analogous in function to conidia. Sporangiospores are formed only by members of the fungal Class known as Zygomycetes (e.g. Rhizopus and Mucor)
Tinea versicolor is characterized by altered coloration of the stratum corneum due to overgrowth of Malassezia furfur, a skin commensal. Involved areas may be lighter or darker than surrounding skin. The altered areas have a bran-like surface and lack inflammation. It usually is not necessary to culture Malassezia furfur due to characteristic skin lesions and its distinctive appearance on direct exam
Skin scrapings directly examined microscopically can be diagnostic for tinea versicolor. Hyphal and yeast-like forms can be seen in a "spaghetti and meatball" configuration When Malassezia furfur is suspected as the etiological agent it is necessary to add sterile olive oil to the surface of the culture media for growth of this lipophilic organism.
The cells of Malassezia furfur are yeast-like and give the appearance of budding. However, the mother cells are actually phialides. The attachment between the mother cell and the daughter cell (phialoconidia) is broad and not constricted as in a true yeast.A collarette is present, however this feature is not readily apparent with brightfield microscopy.
Tinea nigra is characterized by darkly pigmented non-inflammed lesions in the surface of the skin. It is caused by Phaeoannellomyces (Exophiala) werneckii, a darkly pigmented (dematiaceous) mold. A KOH preparation of skin scrapings from a tinea nigra lesion would demonstrate the presence of dark hyphal elements.
Phaeoannellomyces werneckii produces a beige yeast-like colony which matures into a black velvet-napped mold with a black reverse. Done
A preparation of the colony will demonstrate pleomorphic microscopic structures. The age of the colony can limit the features that are seen. Hyphae often do not appear until the colony is mature. The dark yeast-like single and doubled-celled conidia are known to be annellides. Striations which are scars left from previous budding may be seen at the elongated end of the cells.
White piedra is a superficial infection characterized by soft nodules on the shaft of hair. It is caused by Trichosporon beigelii, a yeast-like mold.
While technically a mold, Trichosporon beigelii gives the initial appearance of a yeast. Mature colonies are yellowish white with a suede-like texture. Trichosporon beigelii is readily identified by yeast assimilation tests and morphology when grown on corn meal agar.
Microscopic morphology as seen on corn meal agar or a stained wet mount preparation from a colony may demonstrate true hyphae, pseudohyphae, arthroconidia and blastoconidia. Done
The dermatophytes are a group of molds that infect the skin, hair and nails. The three genera classified as dermatophytes are: Epidermophyton, Microsporum and Trichophyton. Ringworm is a common term for dermatophytosis due to the circular skin lesion. Dermatophytes of human origin usually cause mild, chronic, persistant infections. In contrast, dermatophytes from animals or soil evoke a vigorous inflammatory response that is usually self-limiting.
A KOH preparation of skin scrapings taken from the infected area will demonstrate hyphae and arthrocondia. All genera of dermatophytes have the same morphology on direct examination.
Epidermophyton floccosum causes infections of the skin and nails, but not hair. The obverse of the colony can vary from brownish-yellow to olive gray. The reverse is orange to brown
A microscopic preparation of a E. floccosum colony demonstrates club-shaped macroconidia that may appear singlely or in clusters. The walls of the macroconidia are smooth. Microconidia are not produced.
Microsporum canis causes skin and hair infections. The obverse color of the colony is white with a yellow fringe. The reverse is yellow, which darkens with age.
A microscopic preparation of a Microsporum canis colony will demonstrate spindle shaped macroconidia which have thick walls, rough exteriors, and often taper to curved apical knobs. A few club-shaped microcondidia may be present.
Trichophyton mentagrophytes may infect any body surface. It most frequently causes athlete's foot. The obverse color varies from white to cream. The texture can be downy to powdery. The reverse may be white, yellow, brown, or red brown.
A microscopic preparation of a T. mentagrophytes colony will demonstrate round, clustered microconidia. Spiral hyphae and thin, smooth-walled macroconidia may also be seen.
T. rubrum sometimes resembles T. mentagrophytes. Differential tests may be used to distinguish between these two species. Done
T. mentagrophytes: hair perforation = positive urea = positive BCP-MSG = profuse growth with alkalinization. T. rubrum: hair perforation = negative urea = negative BCP-MSG = restricted growth with no change to pH.
Trichophyton rubrum infects nails and the skin of hands, feet, and torso. It rarely infects hair. The obverse appearance is typically white and downy. The reverse typically is wine red, but may be brown, yellow-orange, or non-pigmented.
A microscopic preparation of a Trichophyton rubrum colony will demonstrate teardrop shaped solitary microconidia. Thin, cigar or pencil-shaped macroconidia may also be present. Differential tests may be necessary to distinguish Trichophyton rubrum from Trichophyton mentagrophytes.
T. rubrum: hair perforation = negative urea = negative BCP-MSG = restricted growth with no change in pH. T. mentagrophytes: hair perforation = positive urea = positive BCP-MSG = profuse growth with alkalinization.
Tricophyton tonsurans commonly causes ringworm of the scalp. It may also infect skin and nails. The obverse appearance is variable. It may be white, gray, yellow, tan or brown. The texture may be powdery to suede-like. The reverse is usually reddish-brown, but sometimes may be yellow or non-pigmented.
A microscopic preparation of a T. tonsurans colony will demonstrate microconidia of variable morphology. The microconidia may appear as teardrops, pegs, clubs or round balloon shapes. Macroconidia are rarely seen. ---->
Nutritional requirement tests using Trichophyton agars can be used to separate T. tonsurans from other Trichophyton species. The growth of T. tonsurans is enhanced by thiamine and grows better on Trichophyton identification agars containing thiamine (agars #3 & #4 rather than on #1 & #2).
Sporotrichosis follows a penetrating wound which inoculates the subcutaneous tissue with a soil mold, Sporothrix schenckii. In developed countries, the typical history involves a deep puncture from a rose thorn. The initial site of inoculation becomes nodular followed by ascending nodules along the lymphatics. If untreated, lesions will ulcerate and drain. Sporothrix is seldom observed on direct examination of material from lesions. Culture usually is required.
Sporothrix schenckii is a thermally dimorphic mold. When cultured at 25-30ºC, it appears as a cream-colored, moist colony which turns brown to black . Short aerial hyphae are usually produced in subculture. At 35-37ºC, the colonies are yeastlike and cream or tan in color.
At 25-30ºC, slender tapering conidiophores are produced at right angles from thin hyphae. A cluster of pear-shaped conidia borne on denticles are produced at the tip of the conidiophore which may be slightly swollen. A second type of conidium is produced along the sides of the hyphae. The conidia turn dark with age. At 35-37ºC, round, oval or elongated budding yeast cells are seen.
Chromoblastomycosis is a chronic disease that follows inoculation of soil molds into subcutaneous tissue. Typical lesions are large warty growths frequently described as cauliflower lesions. 4 orgs cause chromoblastomycosis: Cladophialophora (Cladosporium) carrionii, Phialophora verrucosa, and 2 Fonsecaea spp. Superinfections w/bacteria complicate course of rel painless disease. Histo. section of lesion biopsy -> thick-walled, darkly-pigmented structures (sclerotic bodies).
Colonies of Cladophialophora carrionii grow slowly and tolerate temperatures up to 37º C. The obverse is flat with a slightly raised center, covered with short velvety gray, gray-green or brown mycelium. The reverse is black.
The hyphae are septate and dematiaceous (dark). Laterally and terminally produced conodiophores bear long branching chains of brown, smooth, oval conidia that are easily disrupted. Dark scars on the conidia are typical at the points of attachment.
Colonies of Fonsecaea spp. grow slowly. The obverse appearance is dark green to brown with velvety texture. The reverse is black
Fonsecaea are dematiaceous molds that may produce four types of conidiation. Fonsecaea type: compact conidiophores produce conidia borne on slightly swollen denticles and may give rise to secondary and successive rows of conidia. Fonsecaea are dematiaceous molds that may produce four types of conidiation. Rhinocladiella type: oval conidia are borne on swollen denticles at the tip and along the sides of the conidiophore.
Fonsecaea are dematiaceous molds that may produce four types of conidiation. Cladosporium type: conidiophores produce shield-shaped conidia that bear oval conidia in branching short chains. The conidia have scars of attachment. Fonsecaea are dematiaceous molds that may produce four types of conidiation. Phialophora type: vase-shaped phialides with collarettes produce oval to round conidia.
Phialophora verrucosa is a slow-growing dematiaceous mold. The obverse appearance is dark gray-green, brown or black and velvety to wooly. The reverse is black.
Hyphae are septate and hyaline to brown in color. Vase-shaped or cylindrical phialides are produced laterally and terminally on the hyphae. They may be single or branched. A distinct cup-like collarette forms at the tip of the phialide. Round to oval conidia typically cluster at the tip of the phialide.
Mycetomas are chronic lesions characterized by swelling, draining fibrotic channels (sinuses), and granules of the causative organism. Mycetomas are caused by a number of soil organisms -> -> including filamentous gram-positive bacteria and molds which are introduced into tissue via a puncture wound. From primary subcutaneous lesions, mycetomas errode into contiguous tissues including muscle and bone.
When the sexual form of this mold is present it is called Pseudallescheria boydii, otherwise it is called Scedosporium apiospermum. The colony grows rapidly. The obverse appearance is white and cottony, becoming gray with age. The reverse is tan with darkening areas.
Pseudallescheria boydii produces cleistothecia. Cleistothecia are large brown structures containing oval ascospores, which are released when the cleistothecia bursts. The asexual form, Scedosporium apiospermum, has oval conidia on long slender conidiophores.
Colonies of Exophilala jeanselmei are slow growing with a dark olive to black yeast-like appearance As the colony matures, the texture becomes velvety. The reverse is black.
Exophiala jeanselmei produce profuse oval conidia The conidiogenous cells are annellides. As each conidium is produced, a scar forms at the terminal end of the annellide.
A variety of filamentous bacteria (branching gram-positive rods) found in the soil can cause mycetomas. Nocardia spp. are a common cause of bacterial mycetomas. Nocardia spp. are weakly acid-fast and may appear beaded on stained preparations. In long-standing infections the organism exists in granules, which should be crushed and examined microscopically.
Phaeohyphomycosis is characterized by subcutaneous cysts or diffuse lesions containing darkly-pigmented hyphae. Phaeohyphomycosis is a chronic infection caused by dematiaceous (darkly-pigmented) molds -> Wangiella dermatitidis, Cladophialophora (Xylohypha) bantiana, Exophiala spp., and Phialophora spp. Phaeohyphomycosis can vary in severity depending on their location and size.
Colonies of Wangiella dermatitidis are slow growing. A young colony is black with a yeast-like appearance. As the colony matures, it becomes velvety in texture. The reverse is black.
Wangiella dermatitidis produces profuse conidia The oval yeast-like conidia are formed by conidiogenous cells known as phialides. The phialides are poorly differentiated from the septate hyphae.
Cladophialophora bantiana grows at a moderate rate. Colonies are olive to gray-black with a velvety texture. The reverse is black.
The conidiophores of Cladophialophora bantiana are poorly differentiated from the septate hyphae. The conidiophores produce long chains of oval conidia.
Colonies of Exophiala spp. are slow growing with a dark olive to black yeast-like appearance. As the colony matures, the texture becomes velvety. The reverse is black.
Exophiala spp. produce profuse oval conidia. The conidiogenous cells are annellides. As each conidium is produced, a scar forms at the terminal end of the annellide.
Phialophora richardsiae is a slow-growing dematiaceous mold. The obverse appearance is dark gray-green, brown or black and velvety to wooly. The reverse is black.
Hyphae are septate and hyaline to brown in color. Vase-shaped or cylindrical phialides are produced on the hyphae. They may be single or branched. A saucer-like collarette forms at the tip of the phialide. Round to oval conidia typically cluster at the tip of the phialide.
Cryptococcosis is a primary infection of the lungs which is caused by Cryptococcus neoformans, an encapsulated yeast. In otherwise healthy people, cryptococcosis is usually asymptomatic, or mild and self-limiting. Rare in heathy individuals / common in immunocompromised patients. The CNS most frequent site of dissemination. Skin and viscera are also involved in a small % of patients. Cryptococcus neoformans -> w/w distribution (pigeon droppings)
The India ink preparation is the traditional method used to look for Cyptococcus neoformans in cerebrospinal fluid. The yeast's capsule creates a halo around the cell. The India ink preparation is often replaced by an antigen test which is more sensitive for detection of C. neoformans. Histologic examination of clinical material occasionally reveals intracellular encapsulated yeast.
Colonies of Cryptococcus neoformans are ivory to beige in color and mucoid in texture. Cryptococcus neoformans may be visible on direct Gram stain of cerebrospinal fluid. The yeast cells may vary in size.
Blastomycosis is found primarily in the eastern United States along the major river valleys. It is caused by Blastomyces dermatitidis, a dimorphic fungus, that appears as a yeast in host tissue and as a mold in the environment. Most patients with blastomycosis have self-limiting pulmonary infections. Most cases present with cutaneous lesions reflecting hematogenous dissemination. Other less common sites of dissemination include viscera, bone, and the prostate gland.
The yeast cells of Blastomyces divide with a characteristic broad-based bud. These can be seen on direct examination of clinical specimens. Done
Blastomyces dermatitidis, a thermally dimorphic fungus, - grows as a mold at 25ºC and as a yeast at 37ºC. Mold colonies of Blastomyces are slow-growing and r white to beige w/fluffy texture. The reverse of the mold colony is tan. The yeast colonies are-> cream colored and irreg shaped. Conversion of the mold to the yeast phase (or yeast to mold imp for ID of Blastomyces. DNA probe is commercially available for confirmation. Oval to round conidia form at the end of short conidiophores. yeast form at 37ºC.
Coccidioidomycosis found primarily in the west hemis with endemic areas in semi-arid regions:southwestern US South America. Caused by Coccidioides immitis, a dimorphic fungus, that appears as spherules in host tissue and as a mold in the env. The majority of patients with coccidioidomycosis have pulmonary infections of varying degrees of severity. Patients who develop flu-like symptoms are said to have Valley Fever due to the high incidence in the San Joaquin Valley in California.
Histologic preparations of host tissue reveal the presence of the spherule form of Coccidiodes immitis. These spherules contain endospores. Coccidioides immitis is a mod rapid-growing dimorphic mold. Colonies appear glaborous at first, but soon become white to tan with fluffy aerial hyphae. The reverse is neutral to gray. The conversion of the mold to spherules is not routinely performed in the clinical laboratory.
A DNA probe is available to distinguish Coccidioides from other white fluffy molds. The arthrocondia of Coccidioides are readily airborne and pose a serious hazard to laboratory personnel. Therefore, it is recommended that all molds be handled in a biosafety cabinet.
With age, the hyphae of Coccidioides begin to form arthroconidia The arthroconidia are barrel-shaped and alternate with empty cells (disjunctor cells). The hyphae fragment, releasing arthroconidia which are readily airborne and highly infectious.
Histoplasmosis is caused by Histoplasma capsulatum, a thermally dimorphic fungus, that appears as small, non-encapsulated yeast cells in macrophages in host tissue and as a mold in the environment Histoplasmosis is distributed worldwide. The endemic areas in the United States include the Ohio-Mississippi valleys where the organism is found in soil enriched with bird or bat droppings
Histoplasmosis originates as an asymptomatic or self-limiting, mild pulmonary infection. A small percentage of patients develop chronic pulmonary lesions. Disseminated disease rarely occurs in the normal host, but is common in compromised patients such as those with lymphoma or AIDS.
Histoplasma capsulatum is a slow-growing thermally dimorphic fungus, which grows as a mold at 25ºC and as a yeast at 37ºC. The mold colonies are white to tan and fluffy in texture with a pale yellow reverse. The yeast colonies are cream-colored and may be glabrous. Conversion of the mold to the yeast phase (or yeast to mold) is important for identification of Histoplasma. A DNA probe is available to distinguish Histoplasma from other white fluffy molds
The mold form of Histoplasma capsulatum produces round, warty (tuberculate) macroconidia. Microconidia may also be present At 37ºC, Histoplasma capsulatum produces small, budding yeast cells.
Paracoccidioidomycosis is caused by Paracoccidioides brasiliensis, a thermally dimorphic fungus, that appears as large, multiply budding yeasts in host tissue and as a mold in the environment. Paracoccidioidomycosis is limited to Central and South America. It originates as a mild pulmonary infection that may disseminate hematogenously to the skin. Most patients present with cutaneous lesions and large cervical lymph nodes.
Paracoccidioides brasiliensis is a slow-growing thermally dimorphic fungus, which grows as a mold at 25ºC and as a yeast at 37ºC. Paracoccidioides brasiliensis produces white, velvety mold colonies and the reverse is generally yellow to brown. Yeast colonies are white and creamy. Conversion of the mold to the yeast phase (or yeast to mold) is important for ID of Paracoccidioides.
Mold form of Paracoccidiodes brasiliensis doesnt usually produce distinctive structures. Chlamydoconidia, arthroconidia, and microconidia may be present At 37ºC, Paracocidioides brasiliensis produces yeast cells with multiple buds.
An opportunistic fungus is one that does not cause disease in otherwise healthy individuals. Opportunistic fungi are often found contaminating bacterial and fungal cultures since they are ubiquitous in the environment. When a patient is immuno-compromised due to high dose steroids, neutropenia, HIV, or organ transplants, opportunistic fungi may cause severe infection.
Candida albicans is a yeast that produces white and creamy colonies. Candida albicans can be differentiated from other yeasts by its positive germ tube test. Gram-positive budding yeast cells and pseudohyphae may be seen on direct Gram stains of clinical material
Candida albicans produces blastoconidia (budding yeast) in culture. Aspergillus fumigatus is a rapidly growing mold. The obverse of the colony is blue-green with a velvety textrue which darkens with age. The reverse is neutral to pale yellow.
The conidial heads (the reproductive structure) of Aspergillus fumigatus is composed of several parts. The bulb is known as the vesicle. From the vesicle grow phialides and the phialides produce chains of round conidia. Aspergillus fumigatus produce a single row of phialides (uniserate) growing upward from the top portion of the vesicle. This is known as columnar formation
There are many species in the Aspergillus group. Description of the phialides and their growth pattern is important to differentiate one species from another. Aspergillus flavus is a rapidly growing mold. The obverse of the colony is yellow-green with a downy to powdery texture. The reverse is a neutral to pale yellow
The conidial heads of Aspergillus flavus are radial. The phialides can be uniserate or biserate and produce chains of round conidia. There are many species in the Aspergillus group. Description of the phialides and their growth pattern is important to differentiate one species from another.
Rhizopus spp. is a very rapidly growing cottony mold. The obverse of the colony is light gray-brown. The reverse is pale Rhizopus spp. produce sporangiophores that grow from the non-septate hyphae. The sporangium develops at the end of the sporangiophore and contains the sporangiospores.
Rhizopus produces rhizoids directly below the sporangiophore. This rhizoid position differentiates Rhizopus from the other zygomycetes Mucor spp. is a very rapidly growing mold. The obverse is white becoming gray with age and has a cottony texture. The reverse is white.
The sporaniophore and sporangium of Mucor can resemble that of Rhizopus. Mucor differs from Rhizopus by its lack of rhizoids. done
Pneumocystis carnii is currently considered to be a fungus; it was formerly classified with the protozoa. Since the organism cannot be cultured in the laboratory, Pneumocystis carinii is usually identified by -> staining lung tissue or secretions with the Gram-Weigert stain and/or histologic stains. P. carinii cysts stain blue with Gram-Weigert and are round to oval in shape. Some cysts will stain faint or even appear to be refractile.
Acremonium has a moderate growth rate. The obverse is white, pale yellow, or light pink with a glabrous to powdery texture. The reverse is colorless or pale yellow to light pink. Acremonium have long slender phialides that produce oval, unicellular microconidia that cluster at the tip of the phialide.
The clusters of microconidia are easily disrupted from the tip of the phialide Alternaria is a rapidly growing, dematiaceous mold. The obverse can vary in color from gray to dark brown. The reverse is brown to black
The porocondia of Alternaria are formed in chains and have a club-like shape. Alternaria produces dematiaceous (dark), poroconidia with transverse and longitudinal septa (muriform).
Chrysosporium is a slow to moderately rapid-growing mold. The obverse is white to pale yellow, tan, or pink. The texture varies from powdery to cottony. The reverse is pale yellow to brown. Chrysosporium is a large, diverse group which produce aleurioconidia that are usually unicellular and form at the ends of short conidiophores, intercalary, or directly from the hyphae
Chaetomium is a rapidly growing mold. The obverse is white to gray, with wooly texture. The reverse varies from pale yellow to dark brown. Chaetomium produces a fruiting body called an ascocarp which is covered with hair-like protrusions (setae) and contains large numbers of oval ascospores.
Curvularia is a rapidly growing mold. The obverse is white which darkens with age and has a wooly texture. The reverse is dark brown. Curvularia produce curved poroconidia which arise from bent (geniculate) conidiophores.
The multicellular poroconidia of Curvularia are curved due to the swelling of the central cell. Epicoccum is a rapidly growing mold. The obverse varies in color from yellow to orange that becomes dark brown with age and has a wooly texture. The reverse is dark brown and may have a diffusible pigment.
Epicoccum produces poorly differentiated conidiophores and dark, rough, spherical conidia with transverse and longitudinal septa (muriform). Fusarium is a rapidly growing mold. The obverse is white to pale yellow or pink, and occasionally lavendar with cottony texture. The reverse varies from pale to red to violet or brown.
Fusarium produces two types of conidia. The macroconidia are multicellular, slightly curved, and arise from phialides at the ends of slender conidiophores. The microconidia vary from oval to cylindrical in shape, may be uni- or multicelluar, and cluster at the ends of slender phialides. The microconidia of Fusarium may be confused with the microconidia of Acremonium.
Paecilomyces is a rapidly growing mold. The obverse is white to beige or lavendar and darkens with age and has a powdery or cottony texture. The reverse is colorless to pale brown or yellow. Paecilomyces produces branched conidiophores with thin, elongated phialides from which chains of oval conidia arise.
Paecilomyces differs from Penicillium by its thin, tapering, widely spread phialides. Penicillium is a rapidly growing mold. The obverse is blue-green with a white border and a velvety texture. The reverse is pale or light yellow.
Penicillium produces simple or branched conidiophores with tightly clustered flask-shaped phialides bearing chains of round conidia. Penicillium differs from Paecilomyces by its thick, flask-shaped, tightlly clustered phialides.
Phoma is a rapidly growing mold. The obverse is light to olive gray with a velvety texture. The reverse is pale yellow to dark brown. Phoma produces conidia within a spherical structure called a pycnidium. An opening in the pycnidium (ostiole) allows the mature, oval, unicellular conidia to disburse.
Pithomyces is a very rapidly growing mold. The obverse is pale gray to brown with a wooly texture. The reverse is dark brown to black. Pithomyces produces barrel-shaped, muriform condia on short, poorly differentiated conidiophores.
Scopulariopsis is a moderately rapid growing mold. The obverse is white to light brown with velvety texture. The reverse is light yellow to brown. Scopulariopsis produce cylindrical annellides that give rise to chains of spiny, round conidia with flat bases.
Ulocladium is a moderately rapid-growing mold. The obverse varies from olive-gray to black with a wooly texture. The reverse is black Ulocladium produces dark, rough-walled, muriform poroconidia.
The poroconidia of Ulocladium arise from geniculate (bent) conidiophores
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