Paecilomyces is a contaminant/opportunistic pathogen, found world wide in soil and decaying vegetation. Paecilomyces is a cosmopolitan filamentous fungus which inhabits the soil, decaying plants, and food products. Some species of Paecilomyces are isolated from insects. The telemorphs of Paecilomyces are classified in the genera Byssochlamys, Chromocleista, Talaromyces, and Thermoascus. Paecilomyces is usually considered as a contaminant but may also cause infections in humans and animals. The genus Paecilomyces contains several species. The most common are Paecilomyces lilacinus and Paecilomyces variotii. The color of the colony and certain microscopic features help in differentiation of the Paecilomyces species from each other. Another feature that helps in species identification is thermophilicity. Paecilomyces crustaceus and Paecilomyces variotii are thermophilic and can grow well at temperatures as high as 50? and possibly 60?C.

The phialides are characteristically swollen at the base and gradually narrowed into a long beak. The spores (conidia) are produced in chains from the tips of the phialides, are colourless or brightly pigmented, and are usually rather narrow. Similar to Penicillium, but the chains of spores tend to be widely divergent in Paecilomyces and more parallel in Penicillium. Holomorphs: Byssochlamys, Talaromyces, Thermoascus. Ref: Bissett 1979; Samson 1974. Colonies of Paecilomyces grow rapidly and mature within 3 days. Paecilomyces crustaceus and Paecilomyces variotii are thermophilic and can grow well at temperatures as high as 50? and possibly 60?C. The colonies are flat, powdery or velvety in texture. The color is initially white, and becomes yellow, yellow-green, yellow-brown, olive-brown, pink, or violet, depending on the species. The reverse is dirty white, buff or brown. A sweet aromatic odor may be associated with older cultures.

A common attribute of these fungi is the lack of sexual forms, thereby the name Fungi Imperfecti. The infection cycle of entomopathogenic fungi, including enzyme production on the cuticle, remains one of the most fascinating areas of research involving these organisms. In this cycle, a spore is deposited on the insect cuticle followed by the development of a germ tube (and in some cases by a structure called appresorium) which penetrates the insect. Fungal penetration can also occur through the spiracles, the mouth, and anal opening. Development occurs in the hemolymph with mycelia eventually exiting from the insect, and producing conidia. Insect mortality due to fungal infection has been ascribed to the destruction of insect tissues, the release of toxins, and nutritional deficiencies.Toxin Production and Clinical Significance

Paecilomyces species can cause various infections in humans. These infections are occasionally referred to as paecilomycosis. Corneal ulcer, keratitis, and endophthalmitis due to Paecilomyces may develop following extended wear contact lens use or ocular surgery. Paecilomyces is among the emerging causative agents of opportunistic mycoses in immunocompromised hosts. Direct cutaneous inoculation may lead to these infections. These infections may involve almost any organ or system of human body. Soft tissue, pulmonary, and cutaneous infections, cellulitis onychomycosis, sinusitis, otitis media, endocarditis, osteomyelitis, peritonitis and catheter-related fungemia have all been reported. Paecilomyces species can also cause allergic disorders, such as allergic alveolitis.