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School of Molecular & Biomedical Science |
Penicillium sp.Colonies are usually fast growing, in shades of green, sometimes white, mostly consisting of a dense felt of conidiophores. Microscopically, chains of single-celled conidia (ameroconidia) are produced in basipetal succession from a specialized conidiogenous cell called a phialide. The term basocatenate is often used to describe such chains of conidia where the youngest conidium is at the basal or proximal end of the chain. In Penicillium, phialides may be produced singly, in groups or from branched metulae, giving a brush-like appearance known as a penicillus. The penicillus may contain both branches and metulae (penultimate branches which bear a whorl of phialides). All cells between the metulae and the stipes of the conidiophores are referred to as branches. The branching pattern may be either simple (non-branched or monoverticillate), one-stage branched (biverticillate-symmetrical), two-stage branched (biverticillate-asymmetrical) or three- to more-staged branched. Conidiophores are hyaline and may be smooth- or rough-walled. Phialides are usually flask-shaped, consisting of a cylindrical basal part and a distinct neck, or lanceolate (with a narrow basal part tapering to a somewhat pointed apex). Conidia are globose, ellipsoidal, cylindrical or fusiform, hyaline or greenish, smooth- or rough- walled. Sclerotia may be produced by some species.
Culture of Penicillium sp.
Conidiophores of P. verrucosum var. cyclopium showing Click here for a description of Penicillium marneffeiFor identification, isolates are usually inoculated at three points on Czapek dox agar and potato dextrose agar and incubated at 25C. Most species sporulate within 7 days. Microscopic mounts are best made using a cellotape flag or slide culture preparations mounted in lactophenol cotton blue. A drop of alcohol is usually needed to detach the cellotape flag from the stick, and to act as a wetting agent.
Morphological structures and types of conidiophore branching
MIC data is limited. Antifungal susceptibility testing of individual strains is recommended.
Clinical significance:Many species of Penicillium are common contaminants on various substrates and are known as potential mycotoxin producers. Correct identification is therefore important when studying possible Penicillium contamination of food. Human pathogenic species are rare, however opportunistic infections leading to mycotic keratitis, otomycosis and endocarditis, often following insertion of valve prosthesis have been reported. More recently, pulmonary and disseminated infections have also reported, especially by P. marneffei in AIDS patients.
Mycosis: HyalohyphomycosisFurther reading:Domsch, K.H., W. Gams, and T.H. Anderson. 1980. Compendium of soil fungi. Volume 1. Academic Press, London, UK. Samson, R.A., E.S. Hoekstra, and C.A.N. van Oorschot. 1984. Introduction to food-borne fungi. Centraalbureau voor Schimmelcultures, Baarn, The Netherlands.
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