The relationship of Phialophora verrucosa to Phialophora americana.

Phialophora verrucosa and P. americana, two dematiaceous hyphomycetes, are known to cause chromoblastomycosis. Even though most medical mycologists consider P. americana as synonymous with P. verrucosa, others maintain them as two distinct species on the basis that the phialides of P. americana have deeper collarettes than those of P. verrucosa. Thirty-two isolates, identified either as P. americana or P. verrucosa, were studied for their morphologic, physiologic, and antigenic characteristics to evaluate their taxonomic status. Collarette morphology was found to be a variable character in 12 of the 32 isolates. Those 12 produced phialides with both shallow and deep collarettes. All of the isolates hydrolysed urea within 7 days at 25 degrees C, and failed to liquefy gelatin after 3 weeks at 25 degrees C. None of the isolates decomposed casein, xanthine, or hypoxanthine at the end of 3 weeks at 25 degrees C. All decomposed tyrosine. They grew at 25 degrees C and 37 degrees C, but failed to grow at 40 degrees C. The antigenic relationship between the two species was studied by the exoantigen procedure. The 32 isolates showed close antigenic relatedness. Adsorptions of antisera with homologous and heterologous antigens rendered the antisera free of precipitin bands when studied by the microimmunodiffusion test. The depth of phialide collarettes produced by the two species, being found to be variable character, and the identical nature of the two species with respect to their physiologic and antigenic characteristics, led us to conclude that P. americana should be considered as a synonym of P. verrucosa.