Taxonomic classification
Kingdom: Fungi
Phylum: Ascomycota
Class: Hemiascomycetes
Order: Saccharomycetales
Family: Endomycetaceae
Genus: Pichia
Description and Natural Habitats
The genus Pichia is a teleomorph that produces ascospores. The anamorphs of the species of Pichia are various Candida species. The connection of specific Candida species with their corresponding Pichia teleomorphs is based on observation of the ascospores produced by the Candida isolate or more specifically, on the 28S gene sequence data. Pichia ohmeri has initially been isolated from cucumber brine and is commonly used in food industry for fermentation in pickles, rinds, and fruits. Clinically, Pichia has generally been considered to be a contaminant. However, some Pichia species are now recognized as clinically significant opportunistic pathogens.
Species
Pichia has several species. The most well-known ones are Pichia anomala, Pichia guilliermondii, Pichia norvegensis, and Pichia ohmeri.
See the summary of current and obsolete names, synonyms and teleomorph-anamorph relations for Pichia spp.
Pathogenicity and Clinical Significance
Pichia is now encountered as a rare and emerging causative agent of opportunistic mycoses that develop in immunocompromised patients or cases with other predisposing factors, such as prematurity, low birth weight, long duration of hospital stay, and existence of prosthetic valve [62, 410, 439, 1426]. Pichia ohmeri has been isolated in patients with urinary tract infection [1852], peritonitis [439], prosthetic valve endocarditis [1889], fungemia [232], and disseminated infection [1468]. Pichia anomala has been isolated in an outbreak of nosocomial fungemia in pediatric patients [410], from infections in a surgical intensive care unit [1144], and as colonizers and causative agents of invasive infections in children [1587].
Noteworthy, recent data suggest that the fungicidal activity of the crude toxin of Pichia anomala against various fungal genera may be promising for its potential use in development of novel antifungal agents [353].
Macroscopic Features
Macroscopic Morphology of Pichia is similar to that observed for Candida species [1852].
Microscopic Features
Ascospore production is the essential property that differentiates Pichia from the corresponding Candida species. Acetate ascospore agar, Gorodkowa medium, V-8 medium or 2% glucose malt agar can be used for production of ascospores. Kinyoun stain is used for microscopic examination of asci and ascospores. Each ascus contains 1-4 ascospores. The ascospores are hat-shaped or spheroidal and stain red with Kinyoun stain. The cells other than ascospores take the counterstain [1295].
Susceptibility
Very limited data are available on in vitro susceptibility of Pichia to antifungal agents Amphotericin B, fluconazole, itraconazole, and flucytosine tend to have relatively low MICs against Pichia [439, 1852].
Amphotericin B has been succesfully used in some Pichia infections [439, 1889] while it has failed in some others [232, 1468]. Clinical success has been achieved with fluconazole in a patient with urinary tract infection [1852].