Paecilomyces

Paecilomyces is a genus of filamentous fungi in the phylum Ascomycota. Species within the genus are commonly encountered in soil, decaying organic matter, and indoor environments, where they function as saprotrophs and occasional plant associates. Some members are also explored as biological control agents against nematodes and insects, notably Paecilomyces lilacinus.

Taxonomy and nomenclature have undergone revisions, and several species formerly placed in Paecilomyces have been reassigned to other genera such as Purpureocillium and Lecanicillium. A well-known example is Paecilomyces lilacinus, which in many taxonomic schemes is now called Purpureocillium lilacinum. Because of ongoing changes, literature may vary in the placement of specific species.

Morphologically, Paecilomyces species produce branched conidiophores bearing phialides that generate chains of conidia. Colonies are typically fast-growing and can be white, gray, tan, or lilac, depending on the species. Temperature tolerance varies among species, with some able to grow at higher temperatures.

Ecology and applications: Paecilomyces species are widespread in soil and decaying matter and can be isolated from air and indoor environments. They include both harmless environmental strains and forms with practical uses, such as biocontrol agents, as well as strains with pathogenic potential for plants, animals, or humans under certain conditions.

Medical relevance: Several Paecilomyces species are opportunistic pathogens in humans, especially among immunocompromised individuals. Infections may involve the eye (keratitis), sinuses, lungs, or disseminate systemically. Accurate identification and antifungal susceptibility testing are important due to variable pathogenicity and resistance patterns.