The genus Paecilomyces may be distinguished from the closely related genus Penicillium by having long slender divergent phialides and colonies that are never typically green. 

Paecilomyces species are common environmental moulds and are seldom associated with human infection. However, the species, P. variotii and P. marquandii are emerging as causative agents of mycotic keratitis and of hyalohyphomycosis in the immunocompromised patient. Note: Paecilomyces lilacinus has been transferred to Purpureocillium lilacinum (Luangsa-ard et al. 2011).

Morphological description: 
Colonies are fast growing, powdery or suede-like, gold, green-gold, yellow-brown, lilac or tan, but never green or blue-green as in Penicillium. Phialides are swollen at their bases, gradually tapering into a rather long and slender neck, and occur solitarily, in pairs, as verticils, and in penicillate heads. Long, dry chains of single-celled, hyaline to dark, smooth or rough, ovoid to fusoid conidia are produced in basipetal succession from the phialides.

Molecular identification: 
Molecular phylogeny based on 18S rDNA sequences was done by Luangsa-ard et al. (2004); the genus is polyphyletic.

Key features: 
Long slender divergent phialides and culture pigmentation.

Samson (1974), Domsch et al. (1980), McGinnis (1980), Onions et al. (1981), Rippon (1988), de Hoog et al. (2000, 2015).

Species descriptions

  • Paecilomyces marquandii

    Paecilomyces marquandii is a soil fungus of worldwide distribution from temperate to tropical regions.

    RG-1 organism.

    Culture of Paecilomyces marquandii

    Culture of Paecilomyces marquandii.

    Morphological description: 
    Colonies are fast growing, suede-like to floccose, pale vinaceous to violet-coloured, with a yellow to orange yellow reverse. Conidiophores are erect, arising from submerged hyphae, 50-300 µm in length, bearing loose whorls of branches and phialides. Conidiophore stipes are 2.5-3.0 µm wide, hyaline and smooth-walled. Phialides are swollen at their bases, tapering into a thin, distinct neck. Conidia are ellipsoidal to fusiform, smooth-walled to slightly roughened, hyaline to purple in mass, 2.5-3.0 x 2-2.2 µm. Spherical to ellipsoidal chlamydospores, 3-5 µm diameter are present. No growth at 37C.

    Paecilomyces marquandii conidiophores, phialides and conidia

    Paecilomyces marquandii conidiophores, phialides and conidia.

    Key features: 
    Colony pigmentation with yellow reverse pigment, phialides with swollen bases, smooth conidiophore stipes, presence of chlamydospores, and no growth at 37C. Note: Purpureocillium lilacinum has no yellow reverse pigment, rough-walled conidiophore stipes, absence of chlamydospores and growth at 37C.

    Samson (1974), Domsch et al. (1980, 2007), de Hoog et al. (2000, 2015).

    Antifungal susceptibility: P. marquandii very limited data (Australian national data); MIC µg/mL.

      No ≤0.03 0.06 0.125 0.25 0.5 1 2 4 8 ≥16
    AmB 7       1     1 1 1 3
    VORI 4   1 2     1        
    POSA 2 1   1              
    ITRA 7 1     2 2   1     1
  • Paecilomyces variotii

    Culture of Paecilomyces variotii

    Culture of Paecilomyces variotii.

    Paecilomyces variotii is a common environmental mould that is widespread in composts, soils and food products. It is known from substrates including food, indoor air, wood, soil and carpet dust.

    RG-2 organism.

    Morphological description: 
    Colonies are fast growing, powdery to suede-like, funiculose or tufted, and yellow-brown or sand-coloured. Conidiophores bearing dense, verticillately arranged branches bearing phialides. Phialides are cylindrical or ellipsoidal, tapering abruptly into a long and cylindrical neck. Conidia are subspherical, ellipsoidal to fusiform, hyaline to yellow, smooth-walled, 3-5 x 2-4 µm and are produced in long divergent chains. Chlamydospores are usually present, singly or in short chains, brown, subspherical to pyriform, 4-8 µm in diameter, thick-walled to slightly verrucose.

     P. variotii

    Conidiophores, phialides, conidia and terminal chlamydospores of P. variotii.

    Key features: 
    Yellow-brown colony pigmentation, cylindrical phialides, and presence of chlamydospores.

    Antifungal susceptibility: P. variotii (Australian national data); MIC µg/mL.

      No ≤0.016 0.03 0.06 0.125 0.25 0.5 1 2 4 ≥8
    AmB 33     1 8 7 8 6 3    
    ISAV 4             1     3
    VORI 31 2     1     1 3 4 20
    POSA 30 3 7 7 2 7 4        
    ITRA 3 2 2 7 9 7 6