Page 427 - Review of Medical Microbiology and Immunology ( PDFDrive )

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416
PART V Mycology

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FIGURE 50–4
Candida albicans—thrush in mouth. Note whit-
ish plaques on tongue. (Reproduced with permission from Usatine,
RP et al: The Color Atlas of Family Medicine, New York: McGraw-Hill,
2009. Courtesy of Richard P. Usatine, MD.)
area of inflammation in perineal region. (Reproduced with permis-
sion from Wolff K, Johnson R. Fitzpatrick’s Color Atlas & Synopsis of
Clinical Dermatology. 6th ed. New York: McGraw-Hill, 2009. Copyright
finding that neutropenia predisposes to disseminated Can- FIGURE 50–5 Candida albicans—diaper rash. Note extensive
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© 2009 by The McGraw-Hill Companies, Inc.)
dida infections.
When local or systemic host defenses are impaired, dis-
ease may result. Overgrowth of C. albicans in the mouth
produces white patches called thrush (Figure 50–4). (Note
seen in neutropenic patients with disseminated disease.
that thrush is a pseudomembrane, a term that is defined in
Candida albicans is the most common species to cause dis-
Chapter 7 on page 39.) Vaginitis with itching and discharge
seminated disease in these patients, but C. tropicalis and C.
is favored by high pH, diabetes, or use of antibiotics. Anti-
parapsilosis are important pathogens also.
biotics suppress the normal flora Lactobacillus, which keep
the pH low. As a result, the pH rises, which favors the
growth of Candida.
Skin invasion occurs in warm, moist areas, which
In exudates or tissues, budding yeasts and pseudohyphae
become red and weeping. Fingers and nails become
appear gram-positive and can be visualized by using
involved when repeatedly immersed in water; persons Laboratory Diagnosis
calcofluor-white staining. In culture, typical yeast colonies
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employed as dishwashers in restaurants are commonly
are formed that resemble large staphylococcal colonies.
affected. Thickening or loss of the nail can occur. Diaper
Candida albicans forms germ tubes in serum at 37°C,
rash in infants occurs when wet diapers are not changed
whereas most other species of pathogenic Candida species
promptly (Figure 50–5).
In immunosuppressed individuals, Candida may dis-
formed by C. albicans but not by most other species of Can-
seminate to many organs or cause chronic mucocutaneous
dida. Note that C. dubliniensis also forms chlamydospores
candidiasis (CMC). CMC is a prolonged infection of the
but will not grow at 42°C whereas C. albicans will. Serologic
skin, oral and genital mucosa, and nails that occurs in indi-
testing is rarely helpful.
viduals deficient in T-cell immunity. Patients with muta-
A laboratory test that can identify C. albicans and four
tions in the gene encoding interleukin-17 (IL-17) and the
receptor for IL-17 are predisposed to CMC. After organ
instead of the usual several days was approved in 2014. The
transplantation, patients receiving immunosuppressive
test uses magnetic resonance technology to detect the pres-
drugs to prevent rejection are predisposed to invasive Can- other Candida species in blood cultures in 3 to 5 hours
ence of yeast DNA and then to identify the species.
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dida infections.
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Skin tests with Candida antigens are uniformly positive
Intravenous drug abuse, indwelling intravenous cathe-
in immunocompetent adults and are used as an indicator
ters, and hyperalimentation also predispose to dissemi-
that the person can mount a cellular immune response. A
nated candidiasis, especially right-sided endocarditis and
endophthalmitis (infection within the eye). Candida
skin test is presumed to have deficient cell-mediated immu-
esophagitis, often accompanied by involvement of the
nity. Such a person is anergic, and other skin tests cannot be
stomach and small intestine, is seen in patients with
interpreted. Thus if a person has a negative Candida skin
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