IV. YEASTS

• Yeasts are common causes of _____ and ____ in women and can cause a number of other diseases in individuals who are healthy or immunocompromised.

• vaginitis ; urinary tract infections (UTIs)

• Yeast can cause ____ and ____

• The most common cause of yeast infections is ____

• newborn infections ; meningitis

• C. albicans

Microscopic appearance

• ____ and ____ will show budding yeast.

• _____ are discovered in routine urinalysis

• _____ preparations are used to show the capsule surrounding C. neoformans.

• Saline wet mounts ; Gram stains

• Yeasts

• India ink

Culturing

• Yeasts are grown on ____ at ___

• Yeasts will form ___, mucoid to smooth colonies within several days.

• On blood agar, yeast colonies can resemble nonhemolytic ____colonies.

• SABHI at 22–30°C.

• cream-colored

• Staphylococcus

Culturing

• _____ is used to differentiate Candida spp. by enhancing the formation of fungal elements such as hyphae, pseudohyphae, and conidia.

• Cornmeal agar with Tween 80

Culturing

• ____ will show chlamydospores with clusters of blastoconidia along the hyphae.

• ____ typically produces long-branched pseudohyphae.

• C. albicans

• Candida tropicalis

• Are hyphaelike extensions of young yeast cells showing parallel sides, are nonseptate will not constrict at their point of origin

Germ tubes

• Looks like germ tubes but are septate and constricted at their point of origin.

Pseudohyphae

Germ tube procedure:

Yeasts are incubated with serum at 37°C for up to 3

hours and examined for germ tube production.

Germ tube procedure:

• _____ is positive for germ tube production.

• ____ is used as the negative control; however, some strains can form germ tubes if incubated for more than 3 hours.

• C. albicans

• C. tropicalis

It determines the aerobic utilization of carbohydrates

Carbohydrate assimilation test

Carbohydrate assimilation test

• _____ containing various carbohydrates are inoculated with yeast suspended in ____.

• The medium contains the pH indicator _____.

• The tubes are incubated at _____ and read at __and_

• Use of the carbohydrates results in the formation of ____ colonies

• Agar slants; saline

• bromcresol purple

• room temperature; 7 and 14 days.

• yellow

• Allow for the identification of several species of yeasts.

• The media contain a variety of substrates.

• The ability to metabolize different substrates results in the production of colonies of different colors.

Chromagars

• The most common yeast isolate

• Normal biota of the mucous membranes lining the respiratory, gastrointestinal, and female genital tracts

Candida albicans

Types of candidiasis

1) Thrush (oral cavity)

2) Vulvovaginitis (vagina)

3) Onychomycosis (nail infections)

4) Paronychomycosis (cuticle infections)

• C. albicans can also cause systemic infections, including ____, UTIs, and ___ and lung infections.

• Predisposition to Candida infections includes burns, wounds, ____, _____, pregnancy, leukemia, and immune problems.

• meningitis ; heart

• diabetes mellitus ; antimicrobial therapy ; leukemia

Culture characteristics

• C. albicans grows on most fungal media as well as ___ , ___, ____

• On cornmeal agar with Tween 80, isolates produce ____.

• sheep blood, chocolate, and eosin-methylene blue agars

• chlamydospores

Biochemical test od C.albicans

1. Germ tube: 

2. Urease: 

3. Inositol: 

1. POSITIVE ; Candida dubliniensis is also positive

   and will form chlamydospores.

2. All Candida spp are NEGATIVE except C.krusei 

3. NEGATIVE

• Produces a mild to moderate pulmonary infection

• Can lead to systemic infections and meningitis.

• Also associated with prostate and tissue infections.

Cryptococcus neoformans

• Can be acquired by contact with bat, pigeon, or other bird droppings, in addition to contaminated vegetables, fruit, and milk.

Cryptococcus neoformans

Identifying characteristics for direct specimens

• On Gram stain, the yeasts appear spherical and are not of uniform size.

• Hematoxylin and eosin stains are used to show capsules in tissue

Cryptococcus neoformans

How is the drect antigen test for cryptococcal antigen performed?

Performed on CSF and serum specimens

Biochemical tests

a) Positive for urease and phenol oxidase

b) Inositol utilization positive

c) Negative for nitrate reduction

Cryptococcus neoformans

Culture characteristics: Cryptococcus neoformans

1) ___ to ___ colonies on bird seed or caffeic acid agars

2) Only forms blastoconidia 

Brown to black

blastoconidia 

• Where species associated with human infections, including the human hair infection white piedra

Trichosporon

Can be isolated from the soil, animals, and humans.

Trichosporon spp

Culture characteristics

1) Form cream-colored, smooth colonies on solid media in about 1 week.

2) Hyaline hyphae with blastoconidia and arthroconidia are produced.

Trichosporon spp.

Biochemical tests

a) Positive for urease

b) Can assimilate some carbohydrates

Trichosporon spp.

• Fund in moist environments such as on shower curtainsand toothbrushes.

• They have also been isolated from soil and dairy products.

• Although they have been associated with hospital-acquired infections, they are generally considered commensals or contaminants.

Rhodotorula

• Resemble the Cryptococcus, but they are inositol negative.

• Some species produce a pink pigment

Rhodotorula

• Actually a mold that can be confused with yeast based on colony morphology.

Geotrichum candidum